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Old August 5th, 2007, 01:09 AM   #1
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will a larger ground glass make a difference in the amount of light loss?

Has anyone ever tried to build a 35mm adapter with a 82mm tube, a vibrating beattie focusing )for a larger projection region),a good acromat, and a mount for medium format lenses. I'm curious, if the image is larger that the camera is focusing on and the acromat has a high magnification will a camera like the A1 or hxv200 be able to produce a image with out zooming in on the ground glass, therefore limiting light loss?

this question has been in my head for months.
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Old August 5th, 2007, 12:03 PM   #2
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Are you talking about using medium format lenses on a 35mm image plane? I'm pretty sure that would greatly throw off the focal length measurements of the lenses you use.

Medium format lenses are heavier, bulkier, and more expensive, making them less than ideal for adapters. Also, the higher the power of the achromat, the more expensive as well, and the greater chromatic aberration. The amount of light lost from zooming in is not enough to warrant sacrificing all the benefits of a cost effective 35mm design. Not to mention medium format lenses are darker/slower anyway.

Most cameras have a macro mode that can focus right up to the glass on the front of the camera, as long as they are not zoomed in. I modified a Letus adapter to mount directly up against the glass of my GL2--35mm, not medium format mind you--and it worked fine minus some vignetting problems from not having some kind of fresnel/PCXL optical solution on it. But the light loss difference between that design sans-zoom and the original unmodified requiring zooming in was unnoticeable. Search around on this forum for "modified letus" and you'll find my thread.
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Old August 5th, 2007, 12:28 PM   #3
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Thanks for the responds. with all these different types of 35mm adapters around , I was becoming curious about methods that might be use to improve the quality output and decrease the light loss.

I am still curious about how the Zacuto and HZ-CA13U adapters work, since both boast about losing a half a stop of light or less. Do you know or have a theory about how that are able to accomplish this.

Note: I realize that they are probable using 2 different methods.
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Old August 5th, 2007, 01:15 PM   #4
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Paul,

I have got one more addition to this: with medium format lens you get more shallow DOF than desired. And this will mean stopping down with all associated problems (vignetting, visible grain and most importantly: even more light loss).

Thomas
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