Formula for Mounting Your Newly Made Pinhole

While browsing through the posts at the F295’s forum. I came across a post by Joe VanCleave, that I found very helpful.

His post was the answer to a question posed regarding the mounting of a Pinhole. The opening “in front” of the pinhole is sometimes overlooked when people start building cameras. That is, until you expose your film/paper and find that you have vignetting around the edges. Unless this hasn’t happened or you haven’t read about it the thought may never occur to you.

So taking the opeing size into consideration, a question comes up. “What should the size of an opening be? Of course you can go really large to be safe, but there must be a way to figure out exactly how much clearance is really needed.

Well thanks to Joe’s post, I have been enlightened. Here it is:

Terminology:
“Projection Distance” = distance from pinhole to center of film
“Film Width” = width of film at its widest point
“Film Height” = height of film at it tallest point
“Front Thickness” = thickness of front of camera (including shutter mechanism) in front of pinhole aperture

Therefore:
Front Opening Width = (Film Width/Projection Distance) x Front Thickness

And:
Front Opening Height = (Film Height/Projection Distance) x Front Thickness

“These results will give you the minimal size opening that will allow the image to not be vignetted at the edge of the film; you may want to add ~10% to the size to ensure that bits of fuzz or wood or cardboard fibers don’t obstruct the view.

This also assumes that the pinhole aperture is centered onto the middle of the film.

I usually make the front opening with the same shape and aspect ratio as the film, rather than just a round hole. This helps to ensure that the corners aren’t vignetted” said Joe.

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