An A/D is, if you don't remember, an Analog to Digital converter. The part of your camera that turns your pixel signal into bits and bytes.
In a typical camera you have:
1: A sensor--for this post, one with 10.000.000 pixels (10MP) that collect the photoelectrons light knocks out of the silicon that the sensor is made from.
2--the sensor readout electronics--depending on the number of photoelectrons held in the pixel this produces a voltage that ranges from a few hundred micro volts (no light, just noise, black--black) to 1 volts (full to the top with photoelectrons, about to saturate and bloom, white-white)
3--the sensor post amplifier--this turns on when you change your ISO gain. At the lowest ISO (50, 100, or 200 depending on what ISO number the marketing folks decide will sell the most cameras this year) there is 1 to 1 amplification. This is the true and only ISO value. With film ISO differences are real. With digital it's just jack up the volume-- in steps. 1to1 at ISO 100 up to 16:1 at ISO 1600.
4--the A/D--without getting into the fine points of digital arithmetic a typical 12 bit A/D takes your post amplifier voltage and give it a number that ranges from 0 to 4195. This number take up (surprise, surprise) 12 bit on your memory cards. Which isn't much until you remember you have to store 10,000,000 of these byte and a half for each uncompressed RAW in your memory card
Over the relatively few years (7) since I first bought my first digital camera. I've handled or owned cameras where the A/D s have gone from 8 to 14 bits (x64), the megapixels from about 250,000 (cheap web cams) to 18,000,000 (my friend's 300D) (X72) and memory cards from 16,000,000 bytes (came with the first camera) to 8,000,000,000 (X500)
These improvements are not random--without all of them taken together we would be looking at serious problems in digiphoto land.
5--And finally all the digital stuff--hardware, firmware and software-- ultimately turns those A/D numbers into bright or dark pixels on your computer monitor or wide screen TV
First little secret you won't find in your camera manual. Every digital sensor ever made has a RAW mode. If they didn't camera engineers wouldn't be able to even start designing a camera. Whether or not you find RAW mode in the camera menu is another matter.
My first camera, an Olympus 3020 ($600), didn't have it in the menu. At first I didn't care since I didn't know RAW modes existed. Then I began reverse engineering my 3020, got weird blue sky noise numbers that were too low and went on to the forums to ask the experts what I was doing wrong. The experts had a stack of reasons why my noise readings could be too high, but no one had a convincing argument why they was so low. Except that I wasn't using my nonexistent RAW mode. something they claimed gave accurate noise numbers.
Since buying a new and expensive camera with RAW mode to settle an Internet argument wasn't in the budget. So I worked out a method of correcting my jpeg numbers. That procedure brought my measured dark shadow noise numbers much closer to theory but didn't do anything to explain my too-good-to-be-true blue sky noise numbers.
My reverse engineering project would have ended on that mystery if six month later I had run across a posting about a Russian hacker who'd worked out the procedure and written the DOS program need to unlock RAW on the 3020. With baited breath and some expectation, I redid my test images only to get numbers that closely matched my corrected jpeg numbers.
Using RAW was not the magic solution although it was satisfying to see jpeg fudge factors were correct. Would still be a mystery if I hadn't discovered the 3020 sensor spec sheet which explained all. Be worth another blog posting once I find the hard disk for the computer I was using then and rig it up so I can take off my copy of the data sheet. A Japanese version might be still around but the English version disappeared from the sensor manufacturer's (Sony) website years ago.
Back to this posting. Since my 12 bit A/D has 4000 levels (4196 to be exact but lets keep the math easy). If I take a perfectly exposed shot where the pixels of the brightest highlights has 64000 photoelectrons in them--the capacity of our imaginary camera--my voltage at the A/D is 1 volt and my output is 4000 levels. To fit everything in I must assign 16 photoelectrons to each level.
If I didn't have a sensor post amp, and if I upped the stutter speed to underexposed a stop (how the sensor sees ISO 200) I would end up with 1/2 volts and be using only 2000 of the 4000 A/D levels. And so on until at ISO 1600 I have 1/16 of a volt and 256 levels.
At first glance this may look may look OK. Monitors have 256 levels so each display level gets its own photoelectron- a good fit.
Don't work out that way. Everything starting with the demosaicing firmware in the camera that calculates the red, green and blue channel for the colors on out to the noise reduction routine in the RAW converter needs far more levels to make their digital calculations accurately. Remembers beyond the A/D your signal is only bits and bytes and everything now is accurate calculation.
How much more accurate? When I want to end up with a truly polished image I work with 16 bit arithmetic when I do the RAW conversions.
So that is what ISO does. It fills more levels in the A/D so the rest of the system, in camera and out of camera, has the data needed to do its calculation. No less. And no more.
Thursday, November 19, 2009
Wednesday, November 18, 2009
I often do a google search when I'm writing blog posts. Usually it's to check a fact, formula or site html. But sometimes I hit on something new that causes me revise what I plan to post.
Since decision time is galloping closer--the Young Shakespeare Player's dress rehearsals start on Friday--I must decide how best to photograph them. It's the last good time to show up with a camera. Then it's time off for the Thanksgiving weekend followed by two weekends of performances before the Julius Caesar cast disbands.
But instead of posting test shots of real people shot at a show opening as I promised I'll be hitting you with more posts on theory. This time I discovered a new site--http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/index.html
If the sight of a mathematical formula immediately sends you off to find a celebrity website you may want to skip this one. But if you are mildly mathematically inclined like me the site has the best explanation of the intricacies of camera noise I've found so far. It confirmed some of my suspicions, explained some of the mysteries I've worked on and set me straight on some matters I've gotten flat out wrong.
Like the number of photoelectrons a sensor can hold. My rule of thumb of 1200 photo electrons per square micron of pixel is too small. That number still fits the small sensors I've tested before. But with larger and better made sensors such as the one in my D60 there is room for far more photoelectrons and far more S/N.
Not that I won't be blogging about the show. It was put on by a group of collectors of found photographs-- antique or just plain old photos you find in flea markets or garage sales.
At the opening the speaker was a well known collector of folk art from St Louis. His talk was on the cream of his photo collection--the part that has been on display in a number of art museums. Afterwards he asked me to send him some of the photos I took during his talk. Another reason to work out how to best clean up low light images.
So far I've been concentration on how good a S/N I can obtain from the D60. I've been ignoring the other half of that question. How much S/N do I need?
The image of the Declaration of Independence provides some insight. (Click on it for a larger image.)
It was manufactured by taking a well exposed image and superimposing a gradient of Gaussian noise on top. The S/N varies from less than one on the left to eight on the right. From it you can see you don't need as much S/N to bring out the fine detail as you might have thought.
Since decision time is galloping closer--the Young Shakespeare Player's dress rehearsals start on Friday--I must decide how best to photograph them. It's the last good time to show up with a camera. Then it's time off for the Thanksgiving weekend followed by two weekends of performances before the Julius Caesar cast disbands.
But instead of posting test shots of real people shot at a show opening as I promised I'll be hitting you with more posts on theory. This time I discovered a new site--http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/index.html
If the sight of a mathematical formula immediately sends you off to find a celebrity website you may want to skip this one. But if you are mildly mathematically inclined like me the site has the best explanation of the intricacies of camera noise I've found so far. It confirmed some of my suspicions, explained some of the mysteries I've worked on and set me straight on some matters I've gotten flat out wrong.
Like the number of photoelectrons a sensor can hold. My rule of thumb of 1200 photo electrons per square micron of pixel is too small. That number still fits the small sensors I've tested before. But with larger and better made sensors such as the one in my D60 there is room for far more photoelectrons and far more S/N.
Not that I won't be blogging about the show. It was put on by a group of collectors of found photographs-- antique or just plain old photos you find in flea markets or garage sales.
At the opening the speaker was a well known collector of folk art from St Louis. His talk was on the cream of his photo collection--the part that has been on display in a number of art museums. Afterwards he asked me to send him some of the photos I took during his talk. Another reason to work out how to best clean up low light images.
So far I've been concentration on how good a S/N I can obtain from the D60. I've been ignoring the other half of that question. How much S/N do I need?
The image of the Declaration of Independence provides some insight. (Click on it for a larger image.)
It was manufactured by taking a well exposed image and superimposing a gradient of Gaussian noise on top. The S/N varies from less than one on the left to eight on the right. From it you can see you don't need as much S/N to bring out the fine detail as you might have thought.
Friday, November 13, 2009
Six years ago I discovered both the challenges of reverse engineering a digital camera to discover how it was made and the Internet photography forums where you could enlighten the world about what you discovered. Or thought you discovered. The Internet was just taking off. The few photo forums that were around then were full of discussions, spirited discussions and outright flame wars. A wild and sometimes informative time.
I fell into a polite disagreement with someone about dynamic range or noise or Ansel Adam's zone system or all three--I don't remember the details. To prove my point I decided I needed to experiment. With a series of photographs of an accurately printed zone system chart and some Photoshop magic, I would win the next round of discussions and establish myself as a photography guru to reckon with. (Naivete, thy name is Internet Newbie)
To accomplished this impossible dream I called around to the local camera stores. Only the Camera Company had anything close to what I wanted. For a mere $160 + dollars I could buy a calibrated 21 zone Kodak photographic step tablet no. 2.
My reply was "You gotta be kidding. There must be anything cheaper. I need this to settle an argument in an Internet forum."
Turns out they had the step tablet in stock because a grad student had special ordered it and then never came back to buy it. Since some money was better than no money for something that had been sitting around for years, the owner decided that if I came up with $25 the tablet was mine.
$25 was more then I wanted to spend, but...hey, who else but a true Internet guru would own a calibrated Kodak 21 zone step tablet no 2. If I could slip that fact into my postings it would add a touch of cachet. Didn't' work out that way but over the years I've wasted many hours playing with the step tablet, so I must have gotten my money's worth.
This is my latest setup
The step gauge consists of 21 neutral density filters printed out on a transparent strip. Their optical density ranges from 0.05, almost transparent, to 3.0, 1/1000 transmitting. To use it, I tape it to the black cardboard holder. That slips into the box in the lower picture. For a source, the white foamboard is lit from outside to make a diffuse and evenly illuminated background.
With the camera on the tripod I drape the black T-shirt over it as a drop cloth. Any stray light overwhelms the transmitted light of the more optically dense strips. This shows up as an offset in the imageJ graph where the low transmitting strips aren't close to zero .
Then I set the camera in manual mode and adjust the exposure so the first few zones are over exposed. Then it's a simple matter to increase both the ISO and the shutter speed to take a series of noise profiles with a constant exposure
For the record you don't need to use this or any other tablet or chart to do the experiment. You can take photos of a white card or wall at various exposures to make them as dark or light as you want. The tablet is convenient. And it along with ImageJ makes neat charts for the blog.
I you want to do the experiment you will need one more free program, ufraw. It's the raw converter that come with GIMP, the free version of Photoshop from the Linux people. Or you can download a stand alone version from here. http://ufraw.sourceforge.net/Install.html
It supports far more versions of RAW than the commercial RAW converters including the CHDK hacked versions. With its latest reincarnation, its graphic interface is easier to use than it used to be. Still doesn't do batch conversions yet, but I'm not complaining. It's free and also the only RAW converter I've found that does linear RAW conversions
What so important about that? In the last post I mentioned that once a sensor's data was turned into bits and bytes, there were many software tricks that camera folks could do to hide and mask the true noise. The most common is gamma conversion. It's important and usually necessary but it completely changes how the image and its noise looks.
With a glance, you can see the difference between the two noise profiles. The image in the center is lighter with a greater dynamic range- a clear advantage over the darker image on the far right.
The advantage shifts when you compare the two graphs. The noise is lower in the top graph, the noise profile of the darker image. The noise also decreases as the steps become darker.With the lower graph from the middle image the noise becomes greater as the steps darken
So which is better. Less noise with less dynamic range. Or the other way around.
Neither. Both graphs are from the same RAW file, one taken at ISO 800 with my friend's Canon 5D--one of the lowest noise camera around. The only difference was how they were processed by the ufRAW converter. The darker image is a linear image with no gamma correction. The lighter one has a gamma correction of 2.2.
The linear noise profile is how the sensor sees the world. Close down the lens a stop and you have half the light and half the number of photoelectons. This creates half the voltage for the A/D. (Analog to Digital converter, the hunk of electronics in the camera that turns the sensor signal into bits and bytes.) That's the definition of linear. Double or half what you put it; double or half what go get out.
Gamma correction is non-linear. Why is that important? Your eye-brain system is non-linear too. Your night vision and response to low light is much better than your daylight vision. Microsoft thinks a gamma of 2.2 is the correct correction. Apple says 1.8. Your real gamma as you read this depends on your eyesight, lighting conditions and what you had for breakfast this morning.
Since photon shot noise is in the light, the less the light the less the noise. That's what you see in the linear graph. With a gamma correction you are brightening the darker steps. Another way to look at it is you are amplifying your sensor signal with software just as you do with hardware when you set the camera to a higher ISO setting.
This amplifies the noise. It also amplifies the signal an equal amount. So the S/N ratio is the same.
It's the S/N ratio that has meaning in an image. Not the noise alone. The distinction is important. While this may sound like a quibble, if you don't distinguish between the two, the noise alone can lead you astray.
How far astray. As an example--this is what happened when we compared the 7D, 5D, and my D60 on Friday.
With photon shot noise, the measurement followed theory closely.
At ISO 800 the full frame 5D had a S/N of of 100 when it's sensor was just about to saturate . It had collected 100,000 photoelectrons in its 72 micron square pixel. My D60 had a S/N of 66 with it smaller 1.5 crop sensor. And the D7 with its 18,000,000 pixels jammed into a slightly smaller 1.6 crop sensor had S/N of 57.
No surprises here. With photon shot noise the cameras behaved just as theory predicted.
When it came to true camera noise, the noise at the bottom of the graph where there is almost no light, the results were different. My D60's noise was identical to his 5D's noise which delighted and surprised me. My friend's brand new 7D looked to be twice as noisy as the other two cameras. something that didn't make him grin wildly.
After a closer look at the data on Saturday morning, I called my friend with better news. For reasons I haven't worked out yet, the data from the two Canon cameras wasn't completely linear. This amplified their noise enough to skew their numbers.
With the corrections, the 5D is the quietest of the three cameras, the 7D is a close second and my D60 is about twice as noisy as the other two.
A mild disappointment, but not a surprising one. The Canon CMOS sensors have electronics built into each sensor to control and reduce the noise. That explains their factor of two noise advantage.
And that doesn't mean my D60 is a bad camera. According to the astrophotography web sites where they really worry and know about noise, the 5D's real camera noise is equivalent to 3-5 photoelectrons. So with the high estimate of 10 photo electrons in my D60, I need to collect only 100 photoelectrons in an exposure for the photon shot noise to equal the camera noise.
Be nice to own a full frame camera, but then we are talking big bucks for both the camera body and the lenses big enough to cover a full frame sensor. I can live with what I have.
So my next post will feature real pictures where I push my camera, lenses and noise reduction programs as far as they can conveniently go. It's the questions that prompted these posts on the theory and practice of camera noise.
I fell into a polite disagreement with someone about dynamic range or noise or Ansel Adam's zone system or all three--I don't remember the details. To prove my point I decided I needed to experiment. With a series of photographs of an accurately printed zone system chart and some Photoshop magic, I would win the next round of discussions and establish myself as a photography guru to reckon with. (Naivete, thy name is Internet Newbie)
To accomplished this impossible dream I called around to the local camera stores. Only the Camera Company had anything close to what I wanted. For a mere $160 + dollars I could buy a calibrated 21 zone Kodak photographic step tablet no. 2.
My reply was "You gotta be kidding. There must be anything cheaper. I need this to settle an argument in an Internet forum."
Turns out they had the step tablet in stock because a grad student had special ordered it and then never came back to buy it. Since some money was better than no money for something that had been sitting around for years, the owner decided that if I came up with $25 the tablet was mine.
$25 was more then I wanted to spend, but...hey, who else but a true Internet guru would own a calibrated Kodak 21 zone step tablet no 2. If I could slip that fact into my postings it would add a touch of cachet. Didn't' work out that way but over the years I've wasted many hours playing with the step tablet, so I must have gotten my money's worth.
This is my latest setup
The step gauge consists of 21 neutral density filters printed out on a transparent strip. Their optical density ranges from 0.05, almost transparent, to 3.0, 1/1000 transmitting. To use it, I tape it to the black cardboard holder. That slips into the box in the lower picture. For a source, the white foamboard is lit from outside to make a diffuse and evenly illuminated background.With the camera on the tripod I drape the black T-shirt over it as a drop cloth. Any stray light overwhelms the transmitted light of the more optically dense strips. This shows up as an offset in the imageJ graph where the low transmitting strips aren't close to zero .
Then I set the camera in manual mode and adjust the exposure so the first few zones are over exposed. Then it's a simple matter to increase both the ISO and the shutter speed to take a series of noise profiles with a constant exposureFor the record you don't need to use this or any other tablet or chart to do the experiment. You can take photos of a white card or wall at various exposures to make them as dark or light as you want. The tablet is convenient. And it along with ImageJ makes neat charts for the blog.
I you want to do the experiment you will need one more free program, ufraw. It's the raw converter that come with GIMP, the free version of Photoshop from the Linux people. Or you can download a stand alone version from here. http://ufraw.sourceforge.net/Install.html
It supports far more versions of RAW than the commercial RAW converters including the CHDK hacked versions. With its latest reincarnation, its graphic interface is easier to use than it used to be. Still doesn't do batch conversions yet, but I'm not complaining. It's free and also the only RAW converter I've found that does linear RAW conversions
What so important about that? In the last post I mentioned that once a sensor's data was turned into bits and bytes, there were many software tricks that camera folks could do to hide and mask the true noise. The most common is gamma conversion. It's important and usually necessary but it completely changes how the image and its noise looks.
With a glance, you can see the difference between the two noise profiles. The image in the center is lighter with a greater dynamic range- a clear advantage over the darker image on the far right.The advantage shifts when you compare the two graphs. The noise is lower in the top graph, the noise profile of the darker image. The noise also decreases as the steps become darker.With the lower graph from the middle image the noise becomes greater as the steps darken
So which is better. Less noise with less dynamic range. Or the other way around.
Neither. Both graphs are from the same RAW file, one taken at ISO 800 with my friend's Canon 5D--one of the lowest noise camera around. The only difference was how they were processed by the ufRAW converter. The darker image is a linear image with no gamma correction. The lighter one has a gamma correction of 2.2.
The linear noise profile is how the sensor sees the world. Close down the lens a stop and you have half the light and half the number of photoelectons. This creates half the voltage for the A/D. (Analog to Digital converter, the hunk of electronics in the camera that turns the sensor signal into bits and bytes.) That's the definition of linear. Double or half what you put it; double or half what go get out.
Gamma correction is non-linear. Why is that important? Your eye-brain system is non-linear too. Your night vision and response to low light is much better than your daylight vision. Microsoft thinks a gamma of 2.2 is the correct correction. Apple says 1.8. Your real gamma as you read this depends on your eyesight, lighting conditions and what you had for breakfast this morning.
Since photon shot noise is in the light, the less the light the less the noise. That's what you see in the linear graph. With a gamma correction you are brightening the darker steps. Another way to look at it is you are amplifying your sensor signal with software just as you do with hardware when you set the camera to a higher ISO setting.
This amplifies the noise. It also amplifies the signal an equal amount. So the S/N ratio is the same.
It's the S/N ratio that has meaning in an image. Not the noise alone. The distinction is important. While this may sound like a quibble, if you don't distinguish between the two, the noise alone can lead you astray.
How far astray. As an example--this is what happened when we compared the 7D, 5D, and my D60 on Friday.
With photon shot noise, the measurement followed theory closely.
At ISO 800 the full frame 5D had a S/N of of 100 when it's sensor was just about to saturate . It had collected 100,000 photoelectrons in its 72 micron square pixel. My D60 had a S/N of 66 with it smaller 1.5 crop sensor. And the D7 with its 18,000,000 pixels jammed into a slightly smaller 1.6 crop sensor had S/N of 57.
No surprises here. With photon shot noise the cameras behaved just as theory predicted.
When it came to true camera noise, the noise at the bottom of the graph where there is almost no light, the results were different. My D60's noise was identical to his 5D's noise which delighted and surprised me. My friend's brand new 7D looked to be twice as noisy as the other two cameras. something that didn't make him grin wildly.
After a closer look at the data on Saturday morning, I called my friend with better news. For reasons I haven't worked out yet, the data from the two Canon cameras wasn't completely linear. This amplified their noise enough to skew their numbers.
With the corrections, the 5D is the quietest of the three cameras, the 7D is a close second and my D60 is about twice as noisy as the other two.
A mild disappointment, but not a surprising one. The Canon CMOS sensors have electronics built into each sensor to control and reduce the noise. That explains their factor of two noise advantage.
And that doesn't mean my D60 is a bad camera. According to the astrophotography web sites where they really worry and know about noise, the 5D's real camera noise is equivalent to 3-5 photoelectrons. So with the high estimate of 10 photo electrons in my D60, I need to collect only 100 photoelectrons in an exposure for the photon shot noise to equal the camera noise.
Be nice to own a full frame camera, but then we are talking big bucks for both the camera body and the lenses big enough to cover a full frame sensor. I can live with what I have.
So my next post will feature real pictures where I push my camera, lenses and noise reduction programs as far as they can conveniently go. It's the questions that prompted these posts on the theory and practice of camera noise.
Tuesday, November 10, 2009
And More Noise
Where were we? Ah, yes. I was making a big deal about the noise being in the light not the camera. Like why should anyone care?
Because .... it's fun to know things like...
Since noise is caused be the random arrival of photons that slam into a pixel and knock out photoelectrons, it's statistical. Just like polling voters to see if Mike or Marsha is going to be our next dog-catcher. If Ms Politico Pollster says that Marsha is up by 2%, but her poll has a margin of error of 3.3%,. Mike is still in the running. The pollster called only 1000 voters. To get to a margin of error of 1%, she would need to call 10,000 voters. A bit many for a dog-catcher election.
Your accuracy (or signal to noise) equals N, the number of samples (voters called) divided by the square root of N (noise). Elementary statistics. If statistics is ever elementary
So if you collect a signal of 1000 photoelectrons your noise is 33 photoelectrons. That gives you a signal to noise (S/N) of 33.3 or a margin of error of 3%.
With ImageJ you can measure S/N accurately. Which brings up the too-good-to-be-true problem.
Since photon shot noise--the biggest source of noise in most images--is from the light not the camera there is nothing a camera manufacturer can do to reduce it in the sensor. But once the signal has been digitized and turned into bits and bytes, there are a multitude of software tricks they can use to hide the noise. Some trick are useful and make for better pictures. As for others--let's say some tricks can be overdone.
Big pixels have less noise because they can hold more photoelectrons. They also cost more to make, one of the reasons a new big sensor DSLR body costs from $500 up while a decent small sensor B&S complete with lens starts around $200. So why don't the camera manufactures make better small sensors to get around the noise problem?
Like everything else sensors have limitations. The photoclectrons are nothing more than a pile of static electricity. Same as the static electricity you collect in your finger if you shuffle your feet on the carpet and get zapped when you touch a door knob.
To keep the camera's static electricity inside a pixels there are wall of negative electricity created by the circuity that defines the pixel. If sensor designer tried use more voltage to hold in more photoelectrons they would create holes. I won't go into the solid state physics of holes except to say they are atom sized PacMen that wander around a pixel and gobble up photoelectrons as soon as they are created. Not exactly what anyone would want in their camera.
By my calculations--I've yet to find the value on the Internet-- a well designed pixel can hold up to 1200 photoelectrons per every square micron of silicon real estate. If you overexpose and create more photoelectrons than the camera can handle, it blooms. Blooming, if you don't know the term, is the cause of the big blob of white covering a street light in a night shot. Instead of creating an image with any detail the photoelectrons have overflown into nearby pixels.
My D60's pixels are 38 microns square. Knock off 10% for the circuitry that forms the pixel wall and they have an active area of 34 square microns. So they can hold about 40,000 photoelectrons. This gives a maximum S/N of 200.
When I did the measurements on my D60 yesterday, I'd hoped to calculate that number. A S/N of a 150 wouldn't have surprised me. If it had been lower that a 100, right now I would be emailing about warranty repair.
Instead I measured a S/N of 500. That requires 250,000 photo electrons and over 6 times more silicon than there's in the camera.
A no questions asked much too good to be true moment.
Next blog post. How I did the measurements. And why I suspect this excessive S/N is caused by a bug is Nikon's RAW compression routine.
Finally if you are a glutton for statistics, I recommend my favorite textbook.
to be continued:
Because .... it's fun to know things like...
Since noise is caused be the random arrival of photons that slam into a pixel and knock out photoelectrons, it's statistical. Just like polling voters to see if Mike or Marsha is going to be our next dog-catcher. If Ms Politico Pollster says that Marsha is up by 2%, but her poll has a margin of error of 3.3%,. Mike is still in the running. The pollster called only 1000 voters. To get to a margin of error of 1%, she would need to call 10,000 voters. A bit many for a dog-catcher election.
Your accuracy (or signal to noise) equals N, the number of samples (voters called) divided by the square root of N (noise). Elementary statistics. If statistics is ever elementary
So if you collect a signal of 1000 photoelectrons your noise is 33 photoelectrons. That gives you a signal to noise (S/N) of 33.3 or a margin of error of 3%.
With ImageJ you can measure S/N accurately. Which brings up the too-good-to-be-true problem.
Since photon shot noise--the biggest source of noise in most images--is from the light not the camera there is nothing a camera manufacturer can do to reduce it in the sensor. But once the signal has been digitized and turned into bits and bytes, there are a multitude of software tricks they can use to hide the noise. Some trick are useful and make for better pictures. As for others--let's say some tricks can be overdone.
Big pixels have less noise because they can hold more photoelectrons. They also cost more to make, one of the reasons a new big sensor DSLR body costs from $500 up while a decent small sensor B&S complete with lens starts around $200. So why don't the camera manufactures make better small sensors to get around the noise problem?
Like everything else sensors have limitations. The photoclectrons are nothing more than a pile of static electricity. Same as the static electricity you collect in your finger if you shuffle your feet on the carpet and get zapped when you touch a door knob.
To keep the camera's static electricity inside a pixels there are wall of negative electricity created by the circuity that defines the pixel. If sensor designer tried use more voltage to hold in more photoelectrons they would create holes. I won't go into the solid state physics of holes except to say they are atom sized PacMen that wander around a pixel and gobble up photoelectrons as soon as they are created. Not exactly what anyone would want in their camera.
By my calculations--I've yet to find the value on the Internet-- a well designed pixel can hold up to 1200 photoelectrons per every square micron of silicon real estate. If you overexpose and create more photoelectrons than the camera can handle, it blooms. Blooming, if you don't know the term, is the cause of the big blob of white covering a street light in a night shot. Instead of creating an image with any detail the photoelectrons have overflown into nearby pixels.
My D60's pixels are 38 microns square. Knock off 10% for the circuitry that forms the pixel wall and they have an active area of 34 square microns. So they can hold about 40,000 photoelectrons. This gives a maximum S/N of 200.
When I did the measurements on my D60 yesterday, I'd hoped to calculate that number. A S/N of a 150 wouldn't have surprised me. If it had been lower that a 100, right now I would be emailing about warranty repair.
Instead I measured a S/N of 500. That requires 250,000 photo electrons and over 6 times more silicon than there's in the camera.
A no questions asked much too good to be true moment.
Next blog post. How I did the measurements. And why I suspect this excessive S/N is caused by a bug is Nikon's RAW compression routine.
Finally if you are a glutton for statistics, I recommend my favorite textbook.
to be continued:
Sunday, November 8, 2009
ImageJ--the step by step
1-Download imageJ from http://rsbweb.nih.gov/ij/. There are MAC, Linux, and Windows 32 and 64 bit versions.
2-Install it. With Vista install it in a directory like your documents or downloads. Then it will have full write permissions. It's a Java applet and works a little different that most windows programs.
3-Launch it. You will see the small Image J box. (For don't-want-rewrite-the-software reasons you can't resize it. On an old VGA screen it looked big.)
4-Click on edit-options-plot profile options. Out of the box, ImageJ autoscales. Since there are 256 gray levels (0 black to 255 white) set the minimum Y to 0 and the maximum Y to at least 255. I use a fixed scale if I'm making comparisons since it makes the differences more obvious.
If you are doing something else, set it any way you want. This box only effects how the plot will look. Click OK to set the scaling
5-Click on file and open an image.
6-Right Click on the line icon box (the fifth over). With version 1.42 you can now draw straight, freehand and segmented lines. Pick a type and drag a line in the image you opened.
7-Hit control+K or the MAC equivalent. Or go to analyse-plot profile in the menu bar. ImageJ will calculate and plot out the grey scale values under the line. If you drew it in an area where there is little detail except for noise you will have a noise profile.
8-Enjoy
2-Install it. With Vista install it in a directory like your documents or downloads. Then it will have full write permissions. It's a Java applet and works a little different that most windows programs.
3-Launch it. You will see the small Image J box. (For don't-want-rewrite-the-software reasons you can't resize it. On an old VGA screen it looked big.)
4-Click on edit-options-plot profile options. Out of the box, ImageJ autoscales. Since there are 256 gray levels (0 black to 255 white) set the minimum Y to 0 and the maximum Y to at least 255. I use a fixed scale if I'm making comparisons since it makes the differences more obvious.
If you are doing something else, set it any way you want. This box only effects how the plot will look. Click OK to set the scaling
5-Click on file and open an image.
6-Right Click on the line icon box (the fifth over). With version 1.42 you can now draw straight, freehand and segmented lines. Pick a type and drag a line in the image you opened.
7-Hit control+K or the MAC equivalent. Or go to analyse-plot profile in the menu bar. ImageJ will calculate and plot out the grey scale values under the line. If you drew it in an area where there is little detail except for noise you will have a noise profile.
8-Enjoy
Saturday, November 7, 2009
Fun with imageJ
This blog is a detour or more accurately a jump-ahead from what I'd planned. When I finished the last post I'd planned to talk more about noise theory, have my buddy bring over his cameras for the measurements, post what we discovered and finally talk about imageJ and lay out how anybody, including you, my dear readers, could do the same measurements with your camera(s).
But once my last post was out in the world and I couldn't find the Badger game on TV, I downloaded the latest and greatest version of ImageJ. Once I started to play around with it I discovered some neat things to share.
ImageJ is scientific image analyser. Scientists around the world use it to pull out the data buried in the their images. Then they write their research papers, give them at confrences and publish them in journals that only scientists can understand.
Buried in my images is data on how good the Lightroom noise reduction routine is. From it I can settle which lenses to use for the YSP dress rehersals photos. Then I'll pass the pictures around in person or by email before I publish a few in this blog or on flickr. Same workflow as a research project--just more informal.
Everybody has a research project. ImageJ can be your friend. It comes free from the NIH, the National Institute of Health. So Google and download it. It's fun to play with.
In the 'What is Noise' post I talked about pixels being like penny jars. And how you filled them with photoelectrons (the pennies). And how you could measure your camera noise once you took an image of uniformly illuminated white card.
All true. But I didn't have to do all that.
Using imageJ, I loaded the blowup of Laura's head with no noise reduction. Then I dragged the yellow line down a black area. (Click the image to see it large.) With a control-K, imageJ created a noise profile from the 600 plus pixels under the line and plotted the gray scale values for me.
Gray scale images have 256 tones--255 is pure white and 0 is jet black. From these values you can calculate back to learn the number of photoelectrons in a pixel. But for this experiment I didn't need to do the calculations.
Instead I did the identical thing with the blowup of Laura after noise reduction. One glance and you can see that the noise reduction routine works. Fairly well too.
The next step is to do more comparisons to see which noise reduction programs--I have several--work the best
Once again imageJ has added new features since the last time I downloaded it. I find the free hand line profile neat and useful. In the third image, I've measured the dark background, Laura's hair and her cheek. In the hair, the noise and hair texture is mixed together. Her cheek, however, is smooth but not evenly illuminated.
The noise from the cheek is riding on the downward slope of the graph and is circled in blue. In this jpeg image the cheek noise is a good deal less than the black backgound noise. Why is a subject for another post. It's more complicated than you might think.
But once my last post was out in the world and I couldn't find the Badger game on TV, I downloaded the latest and greatest version of ImageJ. Once I started to play around with it I discovered some neat things to share.
ImageJ is scientific image analyser. Scientists around the world use it to pull out the data buried in the their images. Then they write their research papers, give them at confrences and publish them in journals that only scientists can understand.
Buried in my images is data on how good the Lightroom noise reduction routine is. From it I can settle which lenses to use for the YSP dress rehersals photos. Then I'll pass the pictures around in person or by email before I publish a few in this blog or on flickr. Same workflow as a research project--just more informal.
Everybody has a research project. ImageJ can be your friend. It comes free from the NIH, the National Institute of Health. So Google and download it. It's fun to play with.
In the 'What is Noise' post I talked about pixels being like penny jars. And how you filled them with photoelectrons (the pennies). And how you could measure your camera noise once you took an image of uniformly illuminated white card.
All true. But I didn't have to do all that.
Using imageJ, I loaded the blowup of Laura's head with no noise reduction. Then I dragged the yellow line down a black area. (Click the image to see it large.) With a control-K, imageJ created a noise profile from the 600 plus pixels under the line and plotted the gray scale values for me.
Gray scale images have 256 tones--255 is pure white and 0 is jet black. From these values you can calculate back to learn the number of photoelectrons in a pixel. But for this experiment I didn't need to do the calculations.
Instead I did the identical thing with the blowup of Laura after noise reduction. One glance and you can see that the noise reduction routine works. Fairly well too.
The next step is to do more comparisons to see which noise reduction programs--I have several--work the best
Once again imageJ has added new features since the last time I downloaded it. I find the free hand line profile neat and useful. In the third image, I've measured the dark background, Laura's hair and her cheek. In the hair, the noise and hair texture is mixed together. Her cheek, however, is smooth but not evenly illuminated.
The noise from the cheek is riding on the downward slope of the graph and is circled in blue. In this jpeg image the cheek noise is a good deal less than the black backgound noise. Why is a subject for another post. It's more complicated than you might think.
What is noise?
What is noise? Thought you would never ask.
Here are a few facts about noise you won't find in a camera's hype sheet. Or on the review sites either. While things have gotten better--well regarded review sites like dpreview aren't pontificating absurdities about camera noise like they were a few years ago--but there is still much confusion.
All the facts I'm listing are out on the web somewhere-either in plain language or more often hiding in mathematical formulas. But I think it would be interesting to pull them together in one place. In more or less plain language,
Fact one.
Unlike film which works in a totally different way, digital cameras count photons. Photons are little hunks of light that work like bullets and knock photoelectrons out of the silicon that camera sensors are made out of and into the pixels that sit on the top of the silicon.
(Einstein won his Nobel Prize for working out how this works. He received the honor. His first wife collected the money. It was written in their divorce settlement.)
Fact two
Pixels work like penny banks. If you take a picture of a uniformly illuminated source--a white box by the window lit by a clear sky for instance--all the pixels will collect their photoelectrons, the pennies, during the exposure. Then if you add up all the photoelectrons and divide by the number of pixels in the camera you have your signal which tells you how bright it is outside. To make the math easy, today the signal is 1000 photoelectons. ("pe-" in engineering talk.)
If you empty a penny bank and count the number of pennies that are short or over 1000, that is the noise. For this example lets say you have 33 extra pe- in a pixel--a magic number I will explain in the next post.
Of all the ways to explain and quantify noise, the number of noise photoelctions is the easiest to work with. So we won't get into decibels, the noise numbers loved by electrical engineers. Today your noise is 33 pe- and your signal to noise (S/N) is 33. That's nothing to brag about but it's still a useable S\N
Fact three
The vast majority of the noise you counted is not from your camera. It from the light. I repeat. THE NOISE IS FROM THE LIGHT!
The noise is caused by the random emission of photons from anything that is hot enough to give off light--that means everything in our universe. Sun, flash lamp, candle, your big toe, puddle of liquid air, everything. The amount of light and spectra of the light will vary of course. With a medical tomographic camera your big toe becomes a bright source, but taking off your shoes won't help any if you are shooting a wedding. Still, regardless of where the light comes from, it carries its noise along with it.
What does this mean. Nothing a camera maker has done or ever will do can get rid of this noise--photon shot noise in engineering talk. Short of a trip to a sf alternate universe, the noise is not going to go away.
And if you noticed that I said "vast majority", what are the real numbers. By my calculations, if you own a Canon 5D up to 98 % of the noise comes from the light in a low ISO and bright exposure. And if you don't, with my carry-it-everywhere Oly SP350 up to 95% of the noise come from the light. Something I measured.
If you now think Old Scrib is sprouting total nonsense--his cheapo old tiny sensor SP350 doesn't take clean pictures like a Canon 5D--we'll explore the differences between noise and signal to noise in more detail in the next blog. If you want to understand what's going on inside your camera confusing the two terms can causes much confusion.
We will also get into how you can, with free software and not that much effort, measure how noisy or clean your camera is. A buddy of mine just bought a Canon 7D--their latest that's been on the market for only a few weeks. Next week he's bring over his older 5D and 7D and we will measure and compare them with my D60.
Be new info. Before the review sites post their noise figures. So keep watching the blog.
*edit* Not new info now--but first time bloggers have high hopes of scoping the big sites.
If you see this edit you are the fifth visitor ever, all today, to read this post. Put a comment in the comment box--so I know there is one-- and I'll think up a suitable prize.
To be continued:
Here are a few facts about noise you won't find in a camera's hype sheet. Or on the review sites either. While things have gotten better--well regarded review sites like dpreview aren't pontificating absurdities about camera noise like they were a few years ago--but there is still much confusion.
All the facts I'm listing are out on the web somewhere-either in plain language or more often hiding in mathematical formulas. But I think it would be interesting to pull them together in one place. In more or less plain language,
Fact one.
Unlike film which works in a totally different way, digital cameras count photons. Photons are little hunks of light that work like bullets and knock photoelectrons out of the silicon that camera sensors are made out of and into the pixels that sit on the top of the silicon.
(Einstein won his Nobel Prize for working out how this works. He received the honor. His first wife collected the money. It was written in their divorce settlement.)
Fact two
Pixels work like penny banks. If you take a picture of a uniformly illuminated source--a white box by the window lit by a clear sky for instance--all the pixels will collect their photoelectrons, the pennies, during the exposure. Then if you add up all the photoelectrons and divide by the number of pixels in the camera you have your signal which tells you how bright it is outside. To make the math easy, today the signal is 1000 photoelectons. ("pe-" in engineering talk.)
If you empty a penny bank and count the number of pennies that are short or over 1000, that is the noise. For this example lets say you have 33 extra pe- in a pixel--a magic number I will explain in the next post.
Of all the ways to explain and quantify noise, the number of noise photoelctions is the easiest to work with. So we won't get into decibels, the noise numbers loved by electrical engineers. Today your noise is 33 pe- and your signal to noise (S/N) is 33. That's nothing to brag about but it's still a useable S\N
Fact three
The vast majority of the noise you counted is not from your camera. It from the light. I repeat. THE NOISE IS FROM THE LIGHT!
The noise is caused by the random emission of photons from anything that is hot enough to give off light--that means everything in our universe. Sun, flash lamp, candle, your big toe, puddle of liquid air, everything. The amount of light and spectra of the light will vary of course. With a medical tomographic camera your big toe becomes a bright source, but taking off your shoes won't help any if you are shooting a wedding. Still, regardless of where the light comes from, it carries its noise along with it.
What does this mean. Nothing a camera maker has done or ever will do can get rid of this noise--photon shot noise in engineering talk. Short of a trip to a sf alternate universe, the noise is not going to go away.
And if you noticed that I said "vast majority", what are the real numbers. By my calculations, if you own a Canon 5D up to 98 % of the noise comes from the light in a low ISO and bright exposure. And if you don't, with my carry-it-everywhere Oly SP350 up to 95% of the noise come from the light. Something I measured.
If you now think Old Scrib is sprouting total nonsense--his cheapo old tiny sensor SP350 doesn't take clean pictures like a Canon 5D--we'll explore the differences between noise and signal to noise in more detail in the next blog. If you want to understand what's going on inside your camera confusing the two terms can causes much confusion.
We will also get into how you can, with free software and not that much effort, measure how noisy or clean your camera is. A buddy of mine just bought a Canon 7D--their latest that's been on the market for only a few weeks. Next week he's bring over his older 5D and 7D and we will measure and compare them with my D60.
Be new info. Before the review sites post their noise figures. So keep watching the blog.
*edit* Not new info now--but first time bloggers have high hopes of scoping the big sites.
If you see this edit you are the fifth visitor ever, all today, to read this post. Put a comment in the comment box--so I know there is one-- and I'll think up a suitable prize.
To be continued:
Thursday, November 5, 2009
Hype and Noise
First the hype. Adobe has a new Lightroom 3 beta up on its web site. In the hype pdf they talk about their great new noise reduction algorithm. So I downloaded the beta to see if the new program would be useful during the YSP project--with over 800 images on the disk it's moved from a shoot into a project.
The first thing I noticed when I tried to use noise reduction was half of it wasn't there. The slider for color noise reduction--the ugly blotches of color caused by the demoisaicing--worked. But the slider for luminescence noise--removing the actual noise--was grayed out. A closer reading of the hype on noise reduction--a marketing song and dance to hide the obvious--Adobe might have a gold metal algorithm somewhere but it ain't implemented yet.
So beta 3 isn't going to help the YSP project. Except that it has me looking into how hard I can push the camera using the Lightroom 2 noise reduction. Which may be a bit farther than I first thought.
During the first shoot, I took the first image at ISO 400, 1/125 sec and f5.6. It is, as you can see, a bit on the dark side-3 to 4 stops underexposed. You should barely see Sasha, the girl on the left, since she's in the spotlight. Whether you see Laura, the girl on the right, depend on how your monitor is adjusted.
In Lightroom I upped the 'exposure' 3 stops. for the second image. (what actually going on when you do this is worth a post sometime)
As long as you don't look close image two isn't a complete disaster. But if you do look close--image three, a closeup of Laura's head--you see the noise in all its glory.
But noise can be reduced. In image four I applied Lightroom 2's noise reduction routine.
It has softened and lost detail,an inevitable consequence of noise reduction. Click on the images for a larger view. Compare the hair for the softening and the sleeve and background for the noise reduction. It's not perfect but I've done worse.
So where are we now. If I use my 105mm manual lens wide open at f2.5 I've picked up 2.3 of the 3 stop of underexposure. Since ISO 800 won't add that much more noise, something I decided in the last post, this lens will give a decent exposure.
But now I have another lens I could use. My 55-200mm kit lens is an f4 at 55mm, f4.2 at 70mm and f4.5 at 85mm. So I would lose a stop or more by switching over to that lens.
But it is image stabilized. I could drop the shutter speed to 1/60 or 1/40 sec since I don't have to worry about camera shake. That would pick up the lost stop of exposure.
Time for more experiments. I will duplicate the theater's lighting at home with my variable power flash and start shooting away. With luck, ISO 1600, and noise reduction I might even be able to take onstage headshots at 200mm and f5.6.
The first thing I noticed when I tried to use noise reduction was half of it wasn't there. The slider for color noise reduction--the ugly blotches of color caused by the demoisaicing--worked. But the slider for luminescence noise--removing the actual noise--was grayed out. A closer reading of the hype on noise reduction--a marketing song and dance to hide the obvious--Adobe might have a gold metal algorithm somewhere but it ain't implemented yet.
So beta 3 isn't going to help the YSP project. Except that it has me looking into how hard I can push the camera using the Lightroom 2 noise reduction. Which may be a bit farther than I first thought.
During the first shoot, I took the first image at ISO 400, 1/125 sec and f5.6. It is, as you can see, a bit on the dark side-3 to 4 stops underexposed. You should barely see Sasha, the girl on the left, since she's in the spotlight. Whether you see Laura, the girl on the right, depend on how your monitor is adjusted. 
In Lightroom I upped the 'exposure' 3 stops. for the second image. (what actually going on when you do this is worth a post sometime) As long as you don't look close image two isn't a complete disaster. But if you do look close--image three, a closeup of Laura's head--you see the noise in all its glory.
But noise can be reduced. In image four I applied Lightroom 2's noise reduction routine.
It has softened and lost detail,an inevitable consequence of noise reduction. Click on the images for a larger view. Compare the hair for the softening and the sleeve and background for the noise reduction. It's not perfect but I've done worse.So where are we now. If I use my 105mm manual lens wide open at f2.5 I've picked up 2.3 of the 3 stop of underexposure. Since ISO 800 won't add that much more noise, something I decided in the last post, this lens will give a decent exposure.
But now I have another lens I could use. My 55-200mm kit lens is an f4 at 55mm, f4.2 at 70mm and f4.5 at 85mm. So I would lose a stop or more by switching over to that lens.
But it is image stabilized. I could drop the shutter speed to 1/60 or 1/40 sec since I don't have to worry about camera shake. That would pick up the lost stop of exposure.
Time for more experiments. I will duplicate the theater's lighting at home with my variable power flash and start shooting away. With luck, ISO 1600, and noise reduction I might even be able to take onstage headshots at 200mm and f5.6.
Friday, October 30, 2009
Young Shakespeare Players (YSP)--The Challenges
I'd heard of the YSP. The girl next door, Julie, who posed for several images I've exhibited (or had rejected by the jury), has a school friend who was a member of YSP a few years back. But during this year's Monroe Street Day I'd only intended to do a quick look-see at the theater and snap a few shots. Then it off for a day of street photography where, if I was very lucky, I'd find an image worth submitting to the jury for the show at the American Girl Headquarters in January.
I never left the theater. After speaking with the staff and promising to send a packet of photos to anyone who wanted them, I did my best to become part of the scenery as I snapped away. After 468 images--including one for the American Girl show--I reluctantly had to leave.
I had never done theater photography and once I had my images up on the computer monitor it showed. I'd been in snapshot mode, trying this and that without thinking through all the photographic limitations that effected what I was trying to do. I'd expected underexposure problems so I'd over compensated. Many on-stage images came out a stop overexposed. To shoot into the dark audience area I often set the shutter speed too slow. The lens I was using, my 35mm f1.8, is image stabilized. Young actors aren't. Unacceptable motion blur.
So I had three goals when I dropped by the theater last Sunday--to show the packet of photos I'd salvaged for the earlier photo shoot, to collect the email addresses of anyone who wanted the packet and to work on correcting my techniques.
To quote someone. "Photography is exclusively about light." Or, in this case, lack of it. Move outdoors into a restored Globe Theater on a cloudy day (no harsh shadows) and my problems would disappear.
To shoot in the real theater, I could up the camera's 'misnamed' ISO. Unlike film a digital camera has only ONE ISO, the lowest one. Everything else is just 'turn up the volume, Joe' with all the problems that causes.
Or I could keep the ISO low, mount the camera on a tripod and take long exposures of things that do not move. Somewhere buried in a hard drive are landscape shots I took in the middle of the last total and clear sky lunar eclipse. Not practical here. Young actors move--a lot. Of the shutter speeds I've tested 1/20 is far too slow and I won't post any of those disasters
1/40 is iffy. The assassination of Caesar was taken with my 105 mm f2.5 Nikkor. It's a cult classic lens from the 1970 and under good lighting where I can close down the aperture it becomes the sharpest lens I own. It is also a manual focus, non image stabilized lens which makes things interesting when I mount it on my D60.
I am showing pics so obviously the lens can be made to work. Despite the temptation I won't repeat the rant I posted in an earlier blog except to say that since Nikon doesn't make a Yen on any lens bought on ebay they decided not to go out of their way to make it easy to use manual focus lenses on the D60.
Back to the image. Not a disaster unless you are picky and study it full size and uncompressed. Only this one in the sequence was worth a keeper flag. The others had their share of shake and blur. Part of it was because I wasn't following the handheld rule of old-- use a shutter speed that matches the focal length of the lens--1/100 sec for a 105 mm lens.
1/80 is more reliable. In this scene I had to pick the most interesting of the shots. At 1/80 the disasters show up in the film strip but farther apart.
This and the other image around them were shot at ISO 400. Almost all needed some exposure boost. So it looks like we shoot at ISO 800 next time,
The last photo was taken at 1/160 and ISO 800 using my fastest lens wide open, the 33mm f1.8 . There is plenty of movement here. I shot it in burst mode while Anna, the young dancer, practiced an Irish dance routine on stage. Her part of the image came out well exposed and not excessively noisy. But if I developed the image to bring out the dark background you would see noise. On the D60 ISO 800 is beginning to push it.
So the standard exposure will be 1/80 sec at ISO 800. If the images ends up underexposed and noisy--thanks to all them wavelets I can do something about noise. Image blur is forever.
I never left the theater. After speaking with the staff and promising to send a packet of photos to anyone who wanted them, I did my best to become part of the scenery as I snapped away. After 468 images--including one for the American Girl show--I reluctantly had to leave.
I had never done theater photography and once I had my images up on the computer monitor it showed. I'd been in snapshot mode, trying this and that without thinking through all the photographic limitations that effected what I was trying to do. I'd expected underexposure problems so I'd over compensated. Many on-stage images came out a stop overexposed. To shoot into the dark audience area I often set the shutter speed too slow. The lens I was using, my 35mm f1.8, is image stabilized. Young actors aren't. Unacceptable motion blur.
So I had three goals when I dropped by the theater last Sunday--to show the packet of photos I'd salvaged for the earlier photo shoot, to collect the email addresses of anyone who wanted the packet and to work on correcting my techniques.
To quote someone. "Photography is exclusively about light." Or, in this case, lack of it. Move outdoors into a restored Globe Theater on a cloudy day (no harsh shadows) and my problems would disappear.
To shoot in the real theater, I could up the camera's 'misnamed' ISO. Unlike film a digital camera has only ONE ISO, the lowest one. Everything else is just 'turn up the volume, Joe' with all the problems that causes.
Or I could keep the ISO low, mount the camera on a tripod and take long exposures of things that do not move. Somewhere buried in a hard drive are landscape shots I took in the middle of the last total and clear sky lunar eclipse. Not practical here. Young actors move--a lot. Of the shutter speeds I've tested 1/20 is far too slow and I won't post any of those disasters
1/40 is iffy. The assassination of Caesar was taken with my 105 mm f2.5 Nikkor. It's a cult classic lens from the 1970 and under good lighting where I can close down the aperture it becomes the sharpest lens I own. It is also a manual focus, non image stabilized lens which makes things interesting when I mount it on my D60.I am showing pics so obviously the lens can be made to work. Despite the temptation I won't repeat the rant I posted in an earlier blog except to say that since Nikon doesn't make a Yen on any lens bought on ebay they decided not to go out of their way to make it easy to use manual focus lenses on the D60.
Back to the image. Not a disaster unless you are picky and study it full size and uncompressed. Only this one in the sequence was worth a keeper flag. The others had their share of shake and blur. Part of it was because I wasn't following the handheld rule of old-- use a shutter speed that matches the focal length of the lens--1/100 sec for a 105 mm lens.
1/80 is more reliable. In this scene I had to pick the most interesting of the shots. At 1/80 the disasters show up in the film strip but farther apart.This and the other image around them were shot at ISO 400. Almost all needed some exposure boost. So it looks like we shoot at ISO 800 next time,
The last photo was taken at 1/160 and ISO 800 using my fastest lens wide open, the 33mm f1.8 . There is plenty of movement here. I shot it in burst mode while Anna, the young dancer, practiced an Irish dance routine on stage. Her part of the image came out well exposed and not excessively noisy. But if I developed the image to bring out the dark background you would see noise. On the D60 ISO 800 is beginning to push it.So the standard exposure will be 1/80 sec at ISO 800. If the images ends up underexposed and noisy--thanks to all them wavelets I can do something about noise. Image blur is forever.
Tuesday, October 20, 2009
When does diffraction---
When does diffraction rear its ugly head? A lot sooner than I had thought.
In an earlier post I'd spoke about empty magnification--bigger blurs circles with no extra detail in images with greater than 1:1 magnification. I also hinted about plans to find better lenses that would drag the hidden detail out of those pesky blur circles. I even bought two nikkor enlarger lens--50 and 75 mm--that were touted on a few websites as being almost as good as genuine optimized closeup lens. With winter coming on, now is the time to think of indoor photography projects..
Then I happened on this article published in a machine vision trade journal.
http://www.vision-systems.com/display_article/356315/19/none/none/Feat/Matching-Lenses-and-Sensors
An eye opening article that rearranged my thinking.
I'd known about Airy disks for decades. They are the blur pattern a perfect no aberrations lens would produce. If such a lens existed. At some time during my optical education, I must have even calculated their diameters. But I had no gut feelings about them. Diffraction limits aren't important when you design infrared spectrometers.
A general observation before I confess all my sloppy thinking to my multitude of readers (humor). The Airy Disk Diameter (ADD) where 83 percent of the energy resides is approximately equal to ADD=2.44*f#*wavelength. For red light and f2.8 the ADD is 4.32 microns.
My carry-it-everywhere 8 MP Oly Sp350 has a max aperture of f2.8 and a pixel pitch of 2.2 microns. So with the lens wide open I'm covering 4 pixels with my smallest blur spot because of diffraction. So if you ever questioned whether jamming huge numbers of pixels into tiny sensor had more to do with marketing than with physics, this is your answer.
With macro photography the diffraction problem get worse. The f# in the equation is an approximation for the numerical aperture--a very good approximation with normal photography but one that breaks down with macro photography. So we have another approximation--the exact equation for numerical aperture has the sine of the angle in radians in it so we won't push beyond the approximation--where the real f# is the f# from the camera lens times the (magnification plus 1) So at 1:1 magnification the diffraction blur becomes twice as big as it would be with normal photography.
For good depth of field with 3D objects you need to use small apertures. Apertures with big diffraction pattern--you can see the problems piling on
Bottom line. There are definite limits to how much detail I can see in my macro photos but they were not caused by my lens. So on to other projects.
As for my nikkor enlarger lens, they weren't that expensive and a web site claim they are good ultraviolet lens. And since I have an ultraviolet slide mounted in a slide projector holder----
Until I was writing this I couldn't figure out why anyone would do this. In the visible the slide is black. Then it hit me--slide projector with bright bulb and a cooling fan, add the UV transmitting slide and you have a source for UV fluorescence photos.
Yup--a replacement winter project.
In an earlier post I'd spoke about empty magnification--bigger blurs circles with no extra detail in images with greater than 1:1 magnification. I also hinted about plans to find better lenses that would drag the hidden detail out of those pesky blur circles. I even bought two nikkor enlarger lens--50 and 75 mm--that were touted on a few websites as being almost as good as genuine optimized closeup lens. With winter coming on, now is the time to think of indoor photography projects..
Then I happened on this article published in a machine vision trade journal.
http://www.vision-systems.com/display_article/356315/19/none/none/Feat/Matching-Lenses-and-Sensors
An eye opening article that rearranged my thinking.
I'd known about Airy disks for decades. They are the blur pattern a perfect no aberrations lens would produce. If such a lens existed. At some time during my optical education, I must have even calculated their diameters. But I had no gut feelings about them. Diffraction limits aren't important when you design infrared spectrometers.
A general observation before I confess all my sloppy thinking to my multitude of readers (humor). The Airy Disk Diameter (ADD) where 83 percent of the energy resides is approximately equal to ADD=2.44*f#*wavelength. For red light and f2.8 the ADD is 4.32 microns.
My carry-it-everywhere 8 MP Oly Sp350 has a max aperture of f2.8 and a pixel pitch of 2.2 microns. So with the lens wide open I'm covering 4 pixels with my smallest blur spot because of diffraction. So if you ever questioned whether jamming huge numbers of pixels into tiny sensor had more to do with marketing than with physics, this is your answer.
With macro photography the diffraction problem get worse. The f# in the equation is an approximation for the numerical aperture--a very good approximation with normal photography but one that breaks down with macro photography. So we have another approximation--the exact equation for numerical aperture has the sine of the angle in radians in it so we won't push beyond the approximation--where the real f# is the f# from the camera lens times the (magnification plus 1) So at 1:1 magnification the diffraction blur becomes twice as big as it would be with normal photography.
For good depth of field with 3D objects you need to use small apertures. Apertures with big diffraction pattern--you can see the problems piling on
Bottom line. There are definite limits to how much detail I can see in my macro photos but they were not caused by my lens. So on to other projects.
As for my nikkor enlarger lens, they weren't that expensive and a web site claim they are good ultraviolet lens. And since I have an ultraviolet slide mounted in a slide projector holder----
Until I was writing this I couldn't figure out why anyone would do this. In the visible the slide is black. Then it hit me--slide projector with bright bulb and a cooling fan, add the UV transmitting slide and you have a source for UV fluorescence photos.
Yup--a replacement winter project.
Monday, September 28, 2009
The Kluge
When I first started this macro project I would have been super proud of this fly image. But I have moved on to the Kluge. Or more accurately the Kluge and a more commercial version now that I've added another flash to my collection.
My 35-70 mm Vivitar mounted directly on the camera give me images with magnifications that varies from a 1/10 (40mm) to a 1/4 (70mm) life size. Add extensions tubes and I can push it up to lifesize or greater imagery. With all the problems.
I don't 'hate' tripods. I just prefer not to be bothered with carrying one around. So if I'm doing 'studio' work in the family room I'll set a tripod up, mount the camera and xy stage on it and shoot away.
Shooting bugs out in the fields and gardens is a different matter. My old manual lens aren't image stabilized. I'm certainly not either as I lean forwards and backwards to bring the bug in and out of focus. And the bug (always) and the flower (with any breeze) are moving.
The one time I tried a tripod in the field or more accurately my back yard I followed advice I'd read in a manual. Find a flower that a bug will love, set up tripod , focus on flower, and wait patiently for bug to strike a pose. Took awhile but once one did, I snapped off five images before it flew away.
Woopee, golly gee. Bound to be keepers since the bug was twice as big as the tiny yellow flower I picked.
I ran in the house to examine my macro masterpieces on the computer. OOPS. Big HEAVY bug on TINY little flower bends flower stem and move everything out of focus. So much for the How-To-Take-Buggy-Pics-In-Your-Backyard manual. Time to think up Plan B.
The problem reduces down to light and speed. With a dash of focus thrown in. With the fly image I had bright sunlight. And a stationery bug for once or I wouldn't have posted the image. Something I didn't have in the roughly 100 other shots I took before I captured this keeper. My success to failure ratio wasn't good.
The obvious solution is a flash to freeze all motion--flower, bug and camera shake. Even better I could have the light I needed. Could shoot with a full stack of tubes for magnification and a tiny aperture for depth of field.
The D60 has a built-in flash with both TTL and manual mode. Unfortunately the lens with extension tubes sticks out so far it blocks the light when I move in close for the shot.
I could have also mounted my best flash on the hot shoe to raise it higher--a dedicated Canon flash unfortunately but the garage sale price was so good I couldn't pass it up. It works fine in manual mode on the hot shoe or with my radio controls and I can dial down the power from full to 1/128 power. Be perfect if I could have tilted the flashead downwards.
My 35-70 mm Vivitar mounted directly on the camera give me images with magnifications that varies from a 1/10 (40mm) to a 1/4 (70mm) life size. Add extensions tubes and I can push it up to lifesize or greater imagery. With all the problems.
I don't 'hate' tripods. I just prefer not to be bothered with carrying one around. So if I'm doing 'studio' work in the family room I'll set a tripod up, mount the camera and xy stage on it and shoot away.
Shooting bugs out in the fields and gardens is a different matter. My old manual lens aren't image stabilized. I'm certainly not either as I lean forwards and backwards to bring the bug in and out of focus. And the bug (always) and the flower (with any breeze) are moving.
The one time I tried a tripod in the field or more accurately my back yard I followed advice I'd read in a manual. Find a flower that a bug will love, set up tripod , focus on flower, and wait patiently for bug to strike a pose. Took awhile but once one did, I snapped off five images before it flew away.
Woopee, golly gee. Bound to be keepers since the bug was twice as big as the tiny yellow flower I picked.
I ran in the house to examine my macro masterpieces on the computer. OOPS. Big HEAVY bug on TINY little flower bends flower stem and move everything out of focus. So much for the How-To-Take-Buggy-Pics-In-Your-Backyard manual. Time to think up Plan B.
The problem reduces down to light and speed. With a dash of focus thrown in. With the fly image I had bright sunlight. And a stationery bug for once or I wouldn't have posted the image. Something I didn't have in the roughly 100 other shots I took before I captured this keeper. My success to failure ratio wasn't good.
The obvious solution is a flash to freeze all motion--flower, bug and camera shake. Even better I could have the light I needed. Could shoot with a full stack of tubes for magnification and a tiny aperture for depth of field.
The D60 has a built-in flash with both TTL and manual mode. Unfortunately the lens with extension tubes sticks out so far it blocks the light when I move in close for the shot.
I could have also mounted my best flash on the hot shoe to raise it higher--a dedicated Canon flash unfortunately but the garage sale price was so good I couldn't pass it up. It works fine in manual mode on the hot shoe or with my radio controls and I can dial down the power from full to 1/128 power. Be perfect if I could have tilted the flashead downwards.
So I built the Kluge. Three feet of 1/8 by 1 aluminum strip, a metal switch plate, some hardware and tubing gathering rust in the garage. Add some sawing and drilling and tapping and there you have it. Not exactly something I can fold up and put in a camera bag but the flash mounts beneath the camera so the flash tube and the lens axis are in the same plane.
With it I took the Bee image. And I didn't have to take a hundred plus shots to get it. With good detail too as you can see with the 100% crop of the bee's eye.
And since the mount folds up to fit in a camera bag, I suspect it will compete with the Kluge come spring when the bee are buzzing blooms again.
Wednesday, September 23, 2009
DIY Closeup Lens
Since the 500 mm lens works well if I don't push it beyond its limitations I'm obviously not going to tear it apart to make an achromatic closeup lens. But I did have another candidate--a zoom lens mounted on a twenty year old video camera with an Vidicon vacuum tube and all the high voltage electronic needed to make the tube work. It came with a separate VCR recorder for the big tapes that fit in a waist harness and--I assume--an equally large and missing battery power pack. Totally non working but since the main attraction of the deal was its big camera bag the camera stuff ended up being stashed away in my basement for some future optics project.
Removing The three tiny screws at the front of the lens didn't loosen anything. (Brought to mind some advice I received as a cub designer/draftsman-"If you goof up put a screw in the goof-up holes to fool them all not in the know.") Since I couldn't locate any other screws and don't own a lens retaining ring spanner out came the hacksaw.
Unfortunately I made a bad guess about the length of the lens assembly. I ended up sawing into what turned out to be an air spaced achromatic doublet. Fortunately I noticed the hacksaw chips between the two lens before I sawed the inner holder in half. After I pulled apart the pieces--they were held together by a press fit using paper shims--I ended with a closeup lens that looked terrible but still worked. Since the hacksaw chips were at or near the principle plane of the doublet they cut the lens transmission by a percent or two but didn't show up in the image.
A powerful closeup lens as it turned out with a focal length of 2.5 inches or 16 diopters. A lens that pushes this method of macro photography to its limits. But once I bought a 52-52mm coupling ring out of Hong Kong it turned my 18-55 mm kit lens into a macro lens. Of sorts. At the 18 mm end I'm in pincushion distortion and vignette heaven.
At the more reasonable 55mm end--judge for yourself. While the closeups aren't as sharp as those from the vivitar macro lens and extension tubes, the closeup lens takes up very little room in my camera bag and is far easier to use. There is something to say for auto focusing, metering and vibration reduction in macro photography.
18-55mm kit lens at 55 mm with 16 diaopter close up lens
without closeup lens
Saturday, September 12, 2009
As I mentioned in an earlier post CPM has moved. On the last weekend in the old building they held a garage sale to get rid of what they didn't want to cart away. Among the goodies was an ancient 500 mm Cambron lens that I remembered seeing for sale at an earlier fundraiser.
The Cambron name is not synonymous with quality, but the bigger problem was the oddball bayonet mount that fitted some equally oddball camera of the 1970's. (a Kiev perhaps) So I moved on to buy other things--lightstands, a photoshop book and a Nikon enlarger lens that may make an excellent UV lens if it turns out not to have a coating that blocks UV.
After I'd gone home I had an idea. As a lens the Cambron may have been useless but if I removed the front lens element it might work as an achromatic close up lens. This idea became even more appealing when, after some Internet research ,I discovered the lens was actually a relabeled Tamron--a lens maker noted for its excellent optics.
So I went back over to CPM on Saturday, saw that the lens was sitting where I left it, and came home with my very inexpensive prize. Turns out I was the only customer that showed up that morning and it was, 'you want it--name a price" day.
Later when I was trying to decide if I should borrow or buy a spanner wrench to remove the lens retaining ring or do a cheapie and take a hacksaw to the barrel, I happened to give the oddball bayonet mount a good twist. To my great surprise it loosened slightly and then unscrewed off. I had bought a T-mount lens!
Tamron was and still is a manufacture of after-market lenses. They had invented the T mount forty odd years ago. No matter what brand of camera a prospective customer owned all the salesman in the camera store had to do was to screw on the proper mount to make what was then a $250-300 sale. And all I had to do was get on ebay, buy a Nikon mount, and up my total investment to $15. Love those garage sale lenses.
Warning--at first I thought it was a M42 lens and almost ordered that adapter. The T mount has the same diameter (42 mm) but has a .75 mm thread pitch rather than M42's 1mm pitch.
So what can this lens do?
The duck picture was taken handheld at a Madison conservation park. I hadn't planned to do my first tests that way and had brought along a tripod. But when I set it up I discovered I'd left the mounting screw in my homemade close up kludge (staring in a future post). Using two rules of photographic thumb, when hand held the minimum shutter speed is equal to your focal length (750 mm equiv on my D60) and the sunny 16 rule (iso 800 to go with the lens's widest f#) it was shot at 1/1000sec at ISO 800 and f8.0.
An ok image once it is reduced for posting it is softer than I hoped when it it viewed full size.
The image quality does improve with a smaller f#. The hand held shot of the swing set was taken from my computer room window across the greenway and a 100 yards away. The noise is higher at 1600 ISO but the nuts holding the swings to the top cross bar must be no more than 1/2 inch in diameter. For a comparison the second image was taken with my 35mm "normal" lens.
Now for a few nature shots. I drove to Fish Camp Park where the Yahara river emptied into Lake Kegonsa--a spot where where swans gather. No swans when I arrived. Then as I stepped out of the car to test the lens on the local ducks, I looked up to see a flock of Mute Swans fly in. Twenty seconds of great images with the camera still locked in the trunk--if only I hadn't stopped for a muffin and coffee at PDG.
Oh well. With luck a power boat would come down the river and I could photograph them taking off. Which didn't happen. By the time the only boat I saw came by the swans had swam up river and around a bend. But I did take my share of feeding swan images. This one was taken from about 100 yards at iso 100, f16 and 125 sec using a tripod.
The other two images are of a pair that were hiding in the reeds across the river. After they decided to visit my side of the river I shot them from about 25 yards using the same settings. The image with the flapping winds is uncropped. The one of the head was cropped to remove a sidewalk in the background.
The Cambron name is not synonymous with quality, but the bigger problem was the oddball bayonet mount that fitted some equally oddball camera of the 1970's. (a Kiev perhaps) So I moved on to buy other things--lightstands, a photoshop book and a Nikon enlarger lens that may make an excellent UV lens if it turns out not to have a coating that blocks UV.
After I'd gone home I had an idea. As a lens the Cambron may have been useless but if I removed the front lens element it might work as an achromatic close up lens. This idea became even more appealing when, after some Internet research ,I discovered the lens was actually a relabeled Tamron--a lens maker noted for its excellent optics.
So I went back over to CPM on Saturday, saw that the lens was sitting where I left it, and came home with my very inexpensive prize. Turns out I was the only customer that showed up that morning and it was, 'you want it--name a price" day.
Later when I was trying to decide if I should borrow or buy a spanner wrench to remove the lens retaining ring or do a cheapie and take a hacksaw to the barrel, I happened to give the oddball bayonet mount a good twist. To my great surprise it loosened slightly and then unscrewed off. I had bought a T-mount lens!
Tamron was and still is a manufacture of after-market lenses. They had invented the T mount forty odd years ago. No matter what brand of camera a prospective customer owned all the salesman in the camera store had to do was to screw on the proper mount to make what was then a $250-300 sale. And all I had to do was get on ebay, buy a Nikon mount, and up my total investment to $15. Love those garage sale lenses.
Warning--at first I thought it was a M42 lens and almost ordered that adapter. The T mount has the same diameter (42 mm) but has a .75 mm thread pitch rather than M42's 1mm pitch.
So what can this lens do?
The duck picture was taken handheld at a Madison conservation park. I hadn't planned to do my first tests that way and had brought along a tripod. But when I set it up I discovered I'd left the mounting screw in my homemade close up kludge (staring in a future post). Using two rules of photographic thumb, when hand held the minimum shutter speed is equal to your focal length (750 mm equiv on my D60) and the sunny 16 rule (iso 800 to go with the lens's widest f#) it was shot at 1/1000sec at ISO 800 and f8.0.
An ok image once it is reduced for posting it is softer than I hoped when it it viewed full size.
The image quality does improve with a smaller f#. The hand held shot of the swing set was taken from my computer room window across the greenway and a 100 yards away. The noise is higher at 1600 ISO but the nuts holding the swings to the top cross bar must be no more than 1/2 inch in diameter. For a comparison the second image was taken with my 35mm "normal" lens.
Now for a few nature shots. I drove to Fish Camp Park where the Yahara river emptied into Lake Kegonsa--a spot where where swans gather. No swans when I arrived. Then as I stepped out of the car to test the lens on the local ducks, I looked up to see a flock of Mute Swans fly in. Twenty seconds of great images with the camera still locked in the trunk--if only I hadn't stopped for a muffin and coffee at PDG.
Oh well. With luck a power boat would come down the river and I could photograph them taking off. Which didn't happen. By the time the only boat I saw came by the swans had swam up river and around a bend. But I did take my share of feeding swan images. This one was taken from about 100 yards at iso 100, f16 and 125 sec using a tripod.
The other two images are of a pair that were hiding in the reeds across the river. After they decided to visit my side of the river I shot them from about 25 yards using the same settings. The image with the flapping winds is uncropped. The one of the head was cropped to remove a sidewalk in the background.
<
Sunday, September 6, 2009
As promised--continued
A short one. Due to some accidental keystrokes I published my last post on lens resolution while I was spell checking and otherwise editing it. Since I was still setting up my new laptop--I went with the accident and moved on to other tasks.
Eight X magnification--alas, twas but empty magnification. That means everything was bigger but there was no new detail. Even at 5X magnification I was pushing the ability of the 35mm Minolta lens to resolve detail. The finest 'hairs' on the moth's antenna were 5 pixels wide. This calculated out to be 7 microns wide or about 1/8 the diameter of the average human hair.
And if any of my hundreds of readers (humor, humor) ever want to do this at home the procedure is simple.
Use your version of my trusty machinist rule to see how big the spot you are imaging is. Convert to microns (1/1000 of a millimeter) if your part of the world never got the metric urge. Divide that number by the number of pixels in your sensor to give the micron per pixel number--1.4 in this image.
Then count the number of pixels in the tiny stuff to learn--
a--how big the fine stuff really is.
b--where your lens's resolution craps out.
And how do I know I ran up against case b? Looked at the slide with my microscope.
In an ideal world I'd now upload the microscope image. But the box of slides is buried--I suspect--under the mess of toys, books and other debris in Charlotte's bedroom/toyroom/storeroom. Time for a cleanup. But not today. The weather is too nice this weekend to waste on a cleanup.
So this post maybe continued again
Wednesday, August 19, 2009
Macro/micro and moth antenna
The camera club I belong to--CPM aka The Center for Photography in Madison--has moved downtown. After the last meeting in the old headquarters, I noticed that among the packing boxes there was one labeled 'Free.' Which happens to be my favorite price when it comes to photo equipment.
After checking with the club president that 'Free' really meant free, he told me "Take the whole box if you want " A strong hint since he was about to lock up. So the box and I went home.
Among the junk, and there was a lot of junk, I found a 2x neutral density filter and an Expodisk for setting a custom white balance. They will end up in my camera bag once the adapter rings I ordered from e-bay arrive. One thing I've learned about free stuff, you have to spend money to make it useful.
I also found a busted Minolta film camera with three lenses--a 28mm, 50mm and 135mm. Normally the lenses would have ended up in the busted junk pile. Minolta lenses won't mount on my Nikon and if they did they wouldn't focus properly since the sensors of the two brands aren't the same distance from the mounting flange. But since I'm now doing macro/ micro photography the 28mm lens might be an excellent find.
In an earlier post I mentioned that to closeup purist, macro photography meant your magnification went from 0.1 X (1:10) to 1X (1:1) and micro photography meant it went from 1X (1:1) to whatever magnification you could get away without using an electron scanning microscope.
{You may see the numbers in brackets on a macro lens's spec sheet. A run of the mill macro zoom should reach 1:4. Better and more expensive lens can reach 1:1. To go beyond that into the larger than life size micro mode you usually need extension tubes or other accessories.}
Until I read up on macro/micro photograph I believed the difference between macro and micro was more or less arbitrary. Even more arbitrary was the rule that the size of your bug image on the film or sensor determined whether it was life size or not. Maybe in the film age when you could hold up a slide and see the image the rule made sense. But in the digital age? My D60 sensor might be just under an inch long but I will be looking at the image on a 21 inch monitor .
But there is a bit more science behind that rule than I first thought.
In normal photography the cute girl you are photographing and the tree behind her are far larger than the image in the camera. But when as you move in closer and closer into the world of closeup and then macro photography the size difference become smaller and smaller. Finally you hit the magic 1:1 magnification where interesting things happen.
For starters your camera and your bug will never be closer. The distance between bug and sensor will be 4 times the focal length of your lens (plus or minus any fudge factor caused by principle planes). And that is where it makes major sense to flip the lens and mount it backwards.
Why? With anything except a totally symmetrical lens--identical glass on either side so the two principle planes overlap smack in the center of the lens assembly (not a very useful design)--there is always a good way and a not so good way to arrange your lens elements. While the focal length and image size might end up the same, the aberrations are different.
Anyone who has every looked at a cut out drawing of a modern camera lens's innards knows there is nothing symmetrical about them. Unless you are dealing with a specialize lens--a microscope objective for instance--lenses are always designed to image big things down on to little sensors. Once you start imaging things the opposite way the aberrations can go bad rapidly
So a reversed 28mm lens looked promising. It's 55mm filter threads screwed directly into the mount on my new bellow. For once I didn't have to spend money to use this free-be. And since the shorter the focal length of the lens the more magnification I get per mm of extension, I pulled out my trusty machinist rule to see what the lens gave me- 1/8 of an inch (3mm) visible in the viewfinder. A magnification of 8X (1:8)--now we are cooking.
But what quality of magnification? I had been using 3D flower samples, Queen Anne's Lace, because there is a field full of them behind the house. But because of the DOF and focusing accuracy problems these didn't work all that well at 4X. (See last post for details) At 8X the problems would be worse.
I needed a 2D target with precision detail. But what? In the past I'd used precision targets for testing microscope resolution limits but those babies went for big bucks. Needed to find myself a flat sample with a full range of detail
Then Charlotte came for a visit. We pulled out her new macro/micro equipment--precision optics by Mattel by way of Goodwill.
This jogged a few memory cells. Stashed away somewhere was a box of prepared microscope slides. Once found Charlotte and the dolls did their brand of science while I selected my sample-a section of a moth's antenna.
(to be continued)
After checking with the club president that 'Free' really meant free, he told me "Take the whole box if you want " A strong hint since he was about to lock up. So the box and I went home.
Among the junk, and there was a lot of junk, I found a 2x neutral density filter and an Expodisk for setting a custom white balance. They will end up in my camera bag once the adapter rings I ordered from e-bay arrive. One thing I've learned about free stuff, you have to spend money to make it useful.
I also found a busted Minolta film camera with three lenses--a 28mm, 50mm and 135mm. Normally the lenses would have ended up in the busted junk pile. Minolta lenses won't mount on my Nikon and if they did they wouldn't focus properly since the sensors of the two brands aren't the same distance from the mounting flange. But since I'm now doing macro/ micro photography the 28mm lens might be an excellent find.
In an earlier post I mentioned that to closeup purist, macro photography meant your magnification went from 0.1 X (1:10) to 1X (1:1) and micro photography meant it went from 1X (1:1) to whatever magnification you could get away without using an electron scanning microscope.
{You may see the numbers in brackets on a macro lens's spec sheet. A run of the mill macro zoom should reach 1:4. Better and more expensive lens can reach 1:1. To go beyond that into the larger than life size micro mode you usually need extension tubes or other accessories.}
Until I read up on macro/micro photograph I believed the difference between macro and micro was more or less arbitrary. Even more arbitrary was the rule that the size of your bug image on the film or sensor determined whether it was life size or not. Maybe in the film age when you could hold up a slide and see the image the rule made sense. But in the digital age? My D60 sensor might be just under an inch long but I will be looking at the image on a 21 inch monitor .
But there is a bit more science behind that rule than I first thought.
In normal photography the cute girl you are photographing and the tree behind her are far larger than the image in the camera. But when as you move in closer and closer into the world of closeup and then macro photography the size difference become smaller and smaller. Finally you hit the magic 1:1 magnification where interesting things happen.
For starters your camera and your bug will never be closer. The distance between bug and sensor will be 4 times the focal length of your lens (plus or minus any fudge factor caused by principle planes). And that is where it makes major sense to flip the lens and mount it backwards.
Why? With anything except a totally symmetrical lens--identical glass on either side so the two principle planes overlap smack in the center of the lens assembly (not a very useful design)--there is always a good way and a not so good way to arrange your lens elements. While the focal length and image size might end up the same, the aberrations are different.
Anyone who has every looked at a cut out drawing of a modern camera lens's innards knows there is nothing symmetrical about them. Unless you are dealing with a specialize lens--a microscope objective for instance--lenses are always designed to image big things down on to little sensors. Once you start imaging things the opposite way the aberrations can go bad rapidly
So a reversed 28mm lens looked promising. It's 55mm filter threads screwed directly into the mount on my new bellow. For once I didn't have to spend money to use this free-be. And since the shorter the focal length of the lens the more magnification I get per mm of extension, I pulled out my trusty machinist rule to see what the lens gave me- 1/8 of an inch (3mm) visible in the viewfinder. A magnification of 8X (1:8)--now we are cooking.
But what quality of magnification? I had been using 3D flower samples, Queen Anne's Lace, because there is a field full of them behind the house. But because of the DOF and focusing accuracy problems these didn't work all that well at 4X. (See last post for details) At 8X the problems would be worse.
I needed a 2D target with precision detail. But what? In the past I'd used precision targets for testing microscope resolution limits but those babies went for big bucks. Needed to find myself a flat sample with a full range of detail
Then Charlotte came for a visit. We pulled out her new macro/micro equipment--precision optics by Mattel by way of Goodwill.
This jogged a few memory cells. Stashed away somewhere was a box of prepared microscope slides. Once found Charlotte and the dolls did their brand of science while I selected my sample-a section of a moth's antenna.
(to be continued)
Wednesday, July 22, 2009
And the Ribbon for Best Lens Goes to----
---I can't make up my mind.
When I started this blog entry several days ago I was certain I knew the answer.
I wrote: "---the 35ish year old Canon f1.4 50mm lens--even if it did trip me up a few times before I figured out its quirks. "
I had traced the most confusing of the quirks to a little catch hidden under the lens's locking ring. If I accidentally twist the locking ring and release the catch, it limits how far the iris can close. The iris adjusting ring turned freely and it might say f16--the limit on the lens-- but the opening stops at where the iris happens to be when I accidentally trip the catch
While I'm sure this enables some neat function when the lens is mounted right side up on a proper camera, in macro work the depth of field--the height where everything is in reasonable focus-- is proportional to the iris opening, So why did one set of images look sharp when the next set look so... You get the idea. A strip of tape fixed that problem but it took a while to figure out what was going on.
In normal photography you wouldn't care--the reason you won't find principle planes in the index of most how-to-photography books.
I worked out the position of the principle planes of the Nikon 50 mm using the fact that for 1/1 magnification the distance between the object--a machinist rule-- and the sensor must be 4X the focal length (8 inches) plus any separation of the principle planes. Measured out to be 8 1/16 inches. That lens is clearly symmetrical with the principle planes at the center of the lens
When I started this blog entry several days ago I was certain I knew the answer.
I wrote: "---the 35ish year old Canon f1.4 50mm lens--even if it did trip me up a few times before I figured out its quirks. "
I had traced the most confusing of the quirks to a little catch hidden under the lens's locking ring. If I accidentally twist the locking ring and release the catch, it limits how far the iris can close. The iris adjusting ring turned freely and it might say f16--the limit on the lens-- but the opening stops at where the iris happens to be when I accidentally trip the catch
While I'm sure this enables some neat function when the lens is mounted right side up on a proper camera, in macro work the depth of field--the height where everything is in reasonable focus-- is proportional to the iris opening, So why did one set of images look sharp when the next set look so... You get the idea. A strip of tape fixed that problem but it took a while to figure out what was going on.
A second quirk was caused by a second catch. It is spring loaded and keeps the iris open on my old FTb Cannon camera until I press the shutter. In theory, easily fixed by a rubber band. In practice, not so easily fixed since there was no good place to hook the other end and still be able to adjust the stage up and down. Took a trip to the hardware store before I could kluge up an attachment rod that moved up and down with the stage.
That is where I ended several days ago. I would have have written a few more lines and published the blog if there hadn't be one other mystery to work out. The Canon lens imaged 4.5 mm on the 24mm long sensor for a magnification of 5.3X while the Nikon lens imaged a little less than 6mm for a magnification of 4.1X. Another clear advantage to the Canon-- but why? Both were 50 mm lens. Using geometric optics formulas it shouldn't have made any difference--50mm is 50 mm period.But real world didn't line up with theory. Which meant it had to have something to do with the principle planes.
What are principle planes? you must be asking.Today you would use a computer to trace all light rays needed to calculate a magnification through the series of glass (and sometimes other materials) lens elements that make up a camera lens. Before computers and with more effort you could do the same calculations with a hand calculator. Before calculators and with much much more effort you would use a slide role--the precision machined five foot long version that came complete with its own magnification optics so you could extrapolate between the lines for the necessary accuracy. Before that you would have used a book filled with tables of sines, cosines, tangents and logarithms, plus paper and goose quills.
Sometime near the end of the goose quill era someone came up with the idea of principle planes. With them you could use the simpler formulas of geometric optics that Issac Newton and Carl Friedrich Gauss devised--formulas showing where you would find an image of a candle flame and how big it would be.
With a single symmetrically convex spherical lens-- one with the same amounts of glass ground off on either side and one of the easiest lens to grind--the two principle planes are together in the middle of the lens. With a plano convex lens with one flat side and one strongly curved side, the planes separate. One is against the flat side; the other is at the tip of the curved side. Add another lens element to make a doublet and you can calculate another set of principle planes. Add a third element... and so on. Add certain combinations of lens element and the principle planes don't even end up near any of the glass elements. Like in a telephoto lens. One of its principle planes to floating in space somewhere in front of its lens barrel.
At this point, "So what" and "Why should I care," are valid thoughts.In normal photography you wouldn't care--the reason you won't find principle planes in the index of most how-to-photography books.
But with micro photography--bigger than lifesize photograph-- it's different. Take a lens. Measure the distance from its front principle plane to your bug's eye--z mm. For a magnification of 10X do the simple calculations. Distance from from the second principle plane to the camera ccd =10z. Oops. Your 300mm telephoto lens is not going to work. 10z puts your camera through the ceiling and into the girl's upstairs bedroom.
But enough with the handwaving theory and back to real world.I worked out the position of the principle planes of the Nikon 50 mm using the fact that for 1/1 magnification the distance between the object--a machinist rule-- and the sensor must be 4X the focal length (8 inches) plus any separation of the principle planes. Measured out to be 8 1/16 inches. That lens is clearly symmetrical with the principle planes at the center of the lens
With the Canon lens it was different. One principle plane was close to mounting flange, the other plane was about a inch farther up in the lens. Another clear advantage for the Canon lens--20% more magnification. But during these tests, I came to realize what I took for lower lens resolution was less than perfect focusing. Three dimensional flowers might be more photogenic than lens charts but they aren't ideal for resolution comparisons.
A super cheap resolution chart would be a fresh flower pedal with interesting detail held flat to a card with double sided sticky tape.
But first I had to work out a major problem with the Nikon lens--a major lens flare in the center of the image. How had I managed to miss that earlier?
Turns out that earlier I'd mounted the camera, extension tubes, bellows and lenses in that order. This time I had the bellows above the extension tubes. When I flipped them the glare spot disappeared. Bellows folds make excellent baffles for stray light.
Summery of what I've learned-- I better have my technique down pat before I blog about lens comparisons. And good macro/micro photograph is both science and art.
Where do I go from here? Despite how it might look, I dud take some non-macro pictures recently. Like about ten gigabytes worth this weekend. Butterflies and kids looking at butterflies at Olbrick Gardens on Friday. Circus World and a Wild West reenactment on Sunday. RAW images and burst modes can fill up memory cards quick.
So it might be a while before I'm blogging again about macros. But it will happen.
Sunday, July 19, 2009
X5
The reversing ring showed up in the mail Saturday. This ring screws into the lens's filter threads and mounts it backwards--something that according to the books should improve the image quality. Since I am pushing the resolution of the 50mm garage sale lens I shall have to do some experiments at lower magnification to test that out.
At 5X magnification, five millimeters of the iris adjustment mechanism is focused down on to ~3800 pixels. Since it takes two pixels minimum to resolve a feature this works out to a theoretical resolving power of 380 line elements per millimeter. And since the numbers I've seen posted in the newsgroups and forums for camera lens resolutions range from 40 to 100 lines elements per millimeter, the slight blur in the image I worked to get rid of wasn't caused by my less than perfect focusing. At 5X magnification the 10 megapixel sensor has far more resolution than the lens.
One test for this problem is how much sharpening is needed. On this image I needed a 2.8 pixels radius and a strength of 400 using Adobe Camera RAW. Such grossly overshapening would have totally destroyed a normal image.
Another challenge was illumination. For maximum DOF I shot a f22, the smallest iris opening on the lens. On top of this you add in an exposure factor of 36--the (magnification pus one) squared. I had to clamp my flash 6 inches away from the mechanism and run it a full power to have the needed light. With a 150 watt halogen lamp almost as close--my first attempt--I was so light starved I couldn't see anything in the viewfinder at f22.
The vitals for this image are:
50 mm lens with an extension of 125mm--the maximum the bellows will allow
5 mm by 3.3 mm image area
5 mm by 3.3 mm image area
4 mm from out-of-focus bottom plate to the plate stretching the spring.
ISO 200 at 1/160 sec.
f22 with an exposure factor of 36.
Thursday, July 16, 2009
The Goodies Are Here
Front row--a five part set of extension tubes.
They screw together to hold the lens away from the camera body for greater magnification. When all five tubes are used the total length is 65 mm. Mount my garage sale 50 mm lens and the image/object magnification is greater than 1/1--the traditional boundary between macro and micro photograph.
For about $15 including shipping there is a surprising amount of precision machining in that set. A big bargain if you own the proper lens. More about that below.
Above them is an extension bellows. It stretches out to 144 mm. If I add the tubes I can reach 209 mm for some big time magnification. (With all the expected exposure and Depth of Field challenges of course).
As for quality and considering the price ($52 with shipping) I'd rate it up-to-the-job. While I've used precision stages before with less slop these stages weren't cheap.
Mounted on the bellows is my garage sale 50mm lens. Next to it is the garage sale 35-70 mm zoom.
At the far left is a Canon lens. When more parts arrive, it will be mounted to the macro setup with the camera end pointing out. Depending on the lens design and how the aberrations were corrected, flipped lens can create a cleaner image at high magnification.
Now for the kicker hidden in the fine print. Without the garage sale lens this setup won't work. All type G lens sold with the D60 lack an aperture control ring. You need the electrical connections to open and close the lens aperture--something you will do a lot in macro photography. Nikon does make extension rings and bellows with the electrical wiring but you will pay big bucks. Like $75 a single ring (B&H) vs $15 a five ring set (OEC Camera by way of ebay)
The new macro stuff is sitting on a copy stand. I bought that at a photographic auction cheap--mainly because nobody else was bidding on it. I discovered why when I took it home and tried to do something useful with it . In the days of manually focused film cameras, these stand were necessity for copy work. But with autofocus and almost instant feedback on how sharp the image looks, they lost their resale value.
To finish the set up, there is a x, z stage (up, down and sideways) that I already owned--a leftover from a consultant project.
Now all I needed was something to photograph. To start I dug out the innards of a camera lens that had been sitting in the back of a desk drawer for--enough years for me to forget why it ended up in pieces.
And here is my first macro using this setup
Let the macros begin
Tuesday, July 14, 2009
Should I Cheat?
Should I cheat and delete the last blog before the entire Internet World (humor, humor) learns I have been WRONG!!
Wiki agrees with me--on their macro page they say flat out that, like regular photography, in macro photography short focal length lens have a greater depth of field than long focal length lens. So I am not alone in my WRONGITUDUALISM!!
So what reduced me to this embarrassing state?
Dr Guru 'Ray, Sidney F.' in his Applied Photographic Optics--500+ pages of everything you want to know about lens plus a hell of a lot more--told me that when you get into the macro world where your magnification is close to 1 to 1 you can whack off parts of the DOF equations because they don't amount to much.
After the whacking is complete all you got left is the f#, the circle of confusion. and the magnification. So that means--I hang my head in shame--my S3IS doesn't have a better DOF than the $550 Tamron 90 mm macro lens. Focal lengths don't count in the macro world
But then, since focal length don't count, the S3IS's DOF ain't worse either. It will still hang around my neck. I already own it, so it's a hell of lot cheaper than that new $550 Tamron lens. Besides, with only a small fraction of the fancy lens price, I bought a set of extension tubes and an extension bellows. Shipped yesterday according to this morning's e-mail.
Add in what I already own--suitable garage sale and closeup lens plus an x,y focusing stage left over from an ancient optics project--I can now take macros until the cows come home. Mixed metaphor--until the memory cards melt.
You have been warned! Twice!
Wiki agrees with me--on their macro page they say flat out that, like regular photography, in macro photography short focal length lens have a greater depth of field than long focal length lens. So I am not alone in my WRONGITUDUALISM!!
So what reduced me to this embarrassing state?
Dr Guru 'Ray, Sidney F.' in his Applied Photographic Optics--500+ pages of everything you want to know about lens plus a hell of a lot more--told me that when you get into the macro world where your magnification is close to 1 to 1 you can whack off parts of the DOF equations because they don't amount to much.
After the whacking is complete all you got left is the f#, the circle of confusion. and the magnification. So that means--I hang my head in shame--my S3IS doesn't have a better DOF than the $550 Tamron 90 mm macro lens. Focal lengths don't count in the macro world
But then, since focal length don't count, the S3IS's DOF ain't worse either. It will still hang around my neck. I already own it, so it's a hell of lot cheaper than that new $550 Tamron lens. Besides, with only a small fraction of the fancy lens price, I bought a set of extension tubes and an extension bellows. Shipped yesterday according to this morning's e-mail.
Add in what I already own--suitable garage sale and closeup lens plus an x,y focusing stage left over from an ancient optics project--I can now take macros until the cows come home. Mixed metaphor--until the memory cards melt.
You have been warned! Twice!
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