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jose angel
31-Jan-2018, 12:04
Hi all,
I`m working on a project that will be performed with pinhole images. I have everything but the pinhole, just because I`m somewhat dumb and don`t know which aperture to choose. I`ll use my 8x10" film holders, the camera is a wooden one with a focal lenght near to 140mm.

I just need the pinhole, so after some search I found that the mounted ones from Edmund`s may be the best suited (thickness looks to be 0.001"). At first, I thought to settle on 0.5mm (according to the calculator the optimal focal length is 141mm) but the coverage is 271mm... a bit small (the diagonal of 8x10" format is 316mm, so I`d get some vignetting -actually light fall off-).

The other choice is a 0.6mm pinhole (optimal focal length is then 202mm, -I can modify the camera to hold it-), with a way larger coverage (388mm). Drawback to me is the narrower field of view (aprox. 75 with a FL of 202mm, vs 95 with a FL of 141mm).

So I wonder how much unpleasant the light fall off with the 141mm camera could be; a gradual softening in detail and light could be even interesting; but if the fall off is something like a sharp black border it could be actually ugly. If so, I maybe should go for the longer focal length.

What do you think? Any experience, or sample images? Thank you.

Ted R
31-Jan-2018, 13:20
I don't know the answer but perhaps this might help? https://www.photrio.com/forum/forums/pinhole-photography.75/

xkaes
31-Jan-2018, 13:34
Pinholes have focal lengths sort of. It is the amount of bellows length that creates the sharpest image at infinity. The image circle should not be thought of the same way with actual lenses. The best (sharpest) pinholes are made with the thinnest materials.

My pinholes are:

75mm f224
88mm f231
118mm f291
151mm f329
185mm f364
234mm f409
289mm f455

Check out the bottom of this page:

http://www.subclub.org/fujinon/close-up.htm

Here are two websites to help you calculate the f-stop of your pin-hole(s) and the focal length(s) that will produce the optimal (i.e., sharpest) results:

http://www.mrpinhole.com/index.php

http://pinhole.stanford.edu/pinholemath.htm (http://pinhole.stanford.edu/pinholemath.htm)

Here is an example:

Pinhole Size Calculator MrPinhole.com
Inches mm
Focal Length 5.51 140
Diameter 0.02 0.499
f stop 281
Image Circle 10.6 269

Jim Jones
31-Jan-2018, 18:03
Experience would lead me to the .5mm pinhole for 140mm focal length. There will be considerable fall-0ff, a little over two stops if I recall correctly. There shouldn't be a sharp black cut-off near the edges if the pinhole is made in very thin material. Don't feel obligated to follow anyone's recommendation for the "correct" focal length for any format. Pinhole photography is very tolerant of disregarding such rules.

jose angel
1-Feb-2018, 03:07
Ted and Xkaes thanks for the links, there are many things I missed, very useful info.
Thanks Jim, this is what I was looking for.
So I`ll start with the 0.5 pinhole. I definitely like a gradual fall off, anyway I need to check it on my own images.