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Old May 6th, 2007, 08:23 AM   #1
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Magnifying the aerial image? Grain Reduction

I've been thinking about how one could reduce grain. Most people are into the thinking that if you want to reduce grain you have to either:

a. Make the grain too small for the camera to detect.
b. Make the grain move too fast for the camera to detect.

My thinking was that we could possibly try produce an image from a 35mm lens onto a larger screen. By filming a larger screen, the size of the grain relative to the size of the image we're capturing would be reduced. We've seen this work on the few medium format adapters that have been created, but those are pretty impractical.

I was thinking this could be done by putting an optical element that magnifies the image projected by the 35mm lens in-between the lens and the ground glass.

The cons of this idea are that the size of our rigs would increase, depending on how much the image was magnified. Also, I think there's a potential for increased light loss and internal reflections.

I'm no optical engineer, so debunk this right now if it's not going to happen.
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Old May 6th, 2007, 09:27 AM   #2
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Your idea is exactly why i opted for using mamiya 645 lenses, they "cast" a bigger image unto the GG.

in my set up using the flange depth on the 645 camera, i get a 45mm X 25mm image projected on the GG.


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Old May 6th, 2007, 11:32 AM   #3
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Quote:
Originally Posted by Chris Knight View Post
The cons of this idea are that the size of our rigs would increase, depending on how much the image was magnified. Also, I think there's a potential for increased light loss and internal reflections.

I'm no optical engineer, so debunk this right now if it's not going to happen.
Spreading any image over a broader area causes the image to darken significantly, and we're already losing a lot from the whole adapter setup. It's just too much of a bother for too little a gain. You might as well invest that effort into ways to move the focusing screen or ground glass with good diffusion/low grain.

I have a theory that if the pits in a ground glass element are deep enough, they can be made narrow enough to minimize being seen but still provide ample diffusion. You might want to look at that direction.
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Old May 6th, 2007, 03:10 PM   #4
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I had the same idea some time ago but without magnifying the image produced by the 35mm slr lens.
I built also for someone a vibrating gg-holder for a bigger groundglass.
Because some 35mm (SLR) lenses are producing a bigger imaging circle than 43mm so you can use a wider circle from that gg and also decreasing the grain a little bit. The VH-76 was designed for the 3" thorlabs tube.

best regards
Daniel
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