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