Knife Edges Under Magnification

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Story is simple. My curiosity again. Once I got new macro lens for my Canon EOS 20D and front lenses for it I had to check out what was going on with my blades of course :) What would it look like under magnification? I've examined the edges using strong loupes, up to 10x, but it's rather tedious. You don't see much of the edge, eyes get tired soon, and so on. Besides, 10x isn't that much of the magnification anyways. I wanted to see more. Well, with new equipment I went much further.

How much of a magnification?

 - Numbers are approximately like this: macro lens, that is Canon MP-65E gives 5:1, i.e. 5xlife size magnification. So, the sensor of 4752 x 3168 resolution is filled with 5 times the object size. Now, display that image on the monitor with 1600x1200 or 1920x1200 in my case and you get roughly 225x magnification compared to life size. Pretty good result. Sometimes too much judging from my experience. You can't see big picture from that close, however you can always scale down, remember the original image is 3072x2048 and as usual I use crops of necessary parts.

Equipment used

 - As you already know the digital camera used for all those pictures was the Canon EOS 20D. In 2008 I've upgraded the cam to EOS-50D. The lens used for all the macro photos was Canon EF-S 60mm macro achieving 1:1 size. In addition to those two pieces I had to use Boen front element lens, 4x. and a Copystand. Later, in 2006 I've upgraded macro lens to Canon MP-65E. Which is a bazooka, not a lens. However, does achieve 5:1 magnification, and no need to deal with the front elements. The drawback is that the lens is manual focus, to be precise there is no focusing at all. You have to move the camera to get the image in focus and DOF is pretty much nonexistent.

Some of the pictures were taken w/o copystand, using small tripod, however that did prove very cumbersome and less effective. I had to use stack of paper to elevate subject's so I could focus the lens properly and so on. Very inconvenient. the only time I can see tripod useful for this type of work is when you need a picture from the angle. Since copystand allows only vertical positioning. But so far I never really needed to shoot a picture of the edge from the angle, and in any case it's easier to position the blade at certain angle that the camera. And finally the light. On some occasions I've used natural light, on others copystand's own light source consisting of 4x75W Tungsten bulbs with Al reflectors. Each method has it's own advantages and disadvantages. Tungsten light is easy to control, gets uncomfortably hot very quick and so on. Natural light isn't always available and not easy to control at all :) Does show reflections better which is desirable when trying to show microscopic edge deformations almost impossible to see otherwise. So, in the end there is no perfection in this world, as usual.

The Process

 - if you want short version describing the process of taking macro photos of knife edge then it sux0rz, and big time. If you don't have copy stand and good light then sux0rz tens times more. So, you get the idea. But the results are well worth the effort. At least IMHO they are. Besides usual problems with precise focusing and eye strain associated with that, there are specific problems photographing shiny metallic objects. Dents and rolls are difficult to see on magnified pictures as well, unless light is right and so on. Often I had to use reflections to indicate on the picture where was the damage. Anyway, this is usual learning curve, so hopefully things will improve with my improved techniques and hardware. Ok, now to the macro photos themselves.