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What are the physics of an optical snoot & gobo?

Started May 22, 2021 | Questions thread
OP (unknown member) Forum Member • Posts: 70
Re: What are the physics of an optical snoot & gobo?

Have a look at Bill Claff's Optics Primer if you want to go into more detail.

Damn, I was about to ask if you had any books or resources to recommend to dig into more details about all that, but you beat me to the punch

The simplest thing is to find the sensor to flange distance for your lens, as you suggest, and use that to determine the position of the infinity focus (usually just called the focal point of the lens).

So the M42 flange distance is about 45mm, and it just so happens that I have a M42->NEX adapter that is about 26mm, and a 16mm extension tube. Both together get me pretty close and allows me to put a gobo right at the back of the extension tube.

However I can't focus to infinity with that setup because I'm putting all of that at the end of my snoot, which is not the proper size. So now all I need to do is find some cardboard tubes and try to fashion a snoot myself.

One last question: if I get infinity focus right, am I correct in assuming that the focus marking on the lens would be accurate as well? I.e if I turn the focusing ring to 2 meters, it should focus the projected image to 2 meters right?

Thank you very much for your help!

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