Tilting macro lens

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cactuspic
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Tilting macro lens

Post by cactuspic »

A while ago, I saw an APO 90mm Componon that no one else bid on in an Ebay auction. I bought the lens for approximately $100. I then decided to build a tilting macro lens. I reversed the lens, used parts from an old bellows, some scrapwood and about $15 of hardware. After I built it, but before I could test it, life got complicated, so it sat on a shelf for a good while. This week, I took it out to play a bit. I started cramming extension tubes together to get the magnification . It worked better than I thought it would. A few minutes ago, when I was taking everything apart to put away, I discovered that I had been too excited and inadvertantly attached a teleconverter instead of a tube. Given that I had a so-so teleconverter in the optical path, I am ecstatic about the results. I estimate the magnification to be in the range of 2-3x. Though it was a bit clunky and the design is less than elegant, it is fun to use. I will have to play with it tomorrow.
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Chris S.
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Post by Chris S. »

Cactus,

I like your elegant tilting front standard. :D Some of the tilting stages from the optomechanical companies use a similar approach--nice to have a home-brew version worked out in our pages.

FYI, you might be able to avoid the slight vignetting if you replace the Kenko tubes with cheap non-automatic tubes. These typically have a larger clear aperture than the automatic ones.

--Chris

cactuspic
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Post by cactuspic »

Chris,

In what may be a "snatch defeat from the jaws of victory" moment, the vignetting was added post capture in Lightroom. :) I've not noticed any vignetting problems with the Kenko tubes nor have i noticed any difference when I use the non-automatic tubes. I have attached a version without the vignetting added.

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lothman
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Post by lothman »

wouldn't it be better to tilt as near as possible to the camera in order to avoid vignetting, similar Zoerk does:
http://www.zoerk.com/pages/p_mfs.htm

cactuspic
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Post by cactuspic »

lothman wrote:wouldn't it be better to tilt as near as possible to the camera in order to avoid vignetting, similar Zoerk does:
http://www.zoerk.com/pages/p_mfs.htm
Given that the lens was reversed and that there was significant extension, the image circle should be huge. In my limited understanding of optics, I have come across two causes of vignetting: 1.constricting the pathway between lens and body, and 2. light falloff as you get beyond the center of the image circle. Assuming the the passageway was not constricted and that the light flowed unobstructed between the lens and the sensor, the question to me would be which system gets you closer to the center of the projected image. When I shot my view camera, I don't remember a difference in vignetting if the tilt/swing movements were with the front or the back standard, which I believe is an analogous situation. But since I was not focused on the question, I may have overlooked the answer. I think that someone better versed in the science of optics, such as Rik or Chris would give a far more complete and accurate analysis.

rjlittlefield
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Post by rjlittlefield »

Everything I see about vignetting in this thread appears to be correct. The optical path can indeed be partially blocked by tubes that have small bores, but this effect is mostly seen on full-frame sensors, and is worse with Nikon cameras than with Canon because of the smaller diameter bayonet mount. If the image circle is small, then it's definitely better to tilt near the camera. This is not to reduce symmetric vignetting, but rather to avoid asymmetric vignetting and loss of image quality caused by moving the sensor away from the high quality central region of the image circle. But in cactuspic's case as shown here, the angular tilt is small enough that I would expect the whole sensor to still lie within the high quality region. It would become an issue at some point if more tilt were required.

Edited to add: note that while the linear width of the high quality region gets larger with increasing extension, so does the linear distance of the sensor away from image center. Because of this, I find it simpler to think in terms of the angle rather than the linear dimensions. The sensor has to stay within the high quality central angle of the lens.

--Rik

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