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philcc
1-Dec-2008, 11:09
I'm new to pinhole cameras and just purchased an 8x10 Santa Barbara 150mm wide angle pinhole camera. I'm using Ilford rc paper and I'm still working on figuring out the correct exposure times. Everyone of my shots are overexposed in the center of the frame and underexposed on the outer edges. The overexposed areas are almost circular in shape. Is this a bad pinhole or do I just need a little more time to get the correct exposure times. Subject distances have varied.

Thanks for any help!

Mark Woods
1-Dec-2008, 11:17
This is a vignette and normal for that wide of a lens on an 8x10. It's part of the charm. The only way to get ride of it is to use a circular ND to even out the field. I don't know if it's possible to move the lens further away, but if you do you'll lessen the affect of the vignette.

MW

Andrew
1-Dec-2008, 11:28
this is the place for you to go:
http://www.f295.org/Pinholeforum/forum/Blah.pl

the vignetting is NORMAL and is simple physics. At the film edges the distance from the pinhole aperture is further away from the film and light intensity is less. In fact it falls off in the inverse square of the distance.

or if you like: f = distance / aperture diamater so the effective f stop is a bigger number at the edge

you'll just have to work with this effect rather than against it !!!

Walter Calahan
1-Dec-2008, 12:26
Try film instead of paper. Vignetting is normal. I've used the camera you bought a lot.

Here is a gallery of my working using various 8x10, 4x5 and medium format cameras: http://www.walterpcalahan.com/Cheers/Portfolios/Pages/Washington_DC.html#0

These images were all made on Fuji Provia 100F. See how the edges fall off.

philcc
2-Dec-2008, 10:45
Thanks for all the responses. Here are some shots I took yesterday. The images are unedited.
http://web.me.com/ftmcctx/Site/Photos.html

philcc
2-Dec-2008, 21:00
Thanks for all the help! Here are some shots from yesterday.

Andrew
2-Dec-2008, 23:38
good pinhole images.... I don't think the vignette is excessive for the equipment you're using

if you're using paper do you pre-flash it ??? if not, you might consider experimenting.

http://www.f295.org/Pinholeforum/forum/Blah.pl?m-1153793328/

Chuck Pere
3-Dec-2008, 05:49
Seems a little bit excessive. My Leonardo 8x10 pinhole has a 3in lens and while having lots of drop off does cover the corners without total vignetting. I'm still in the put the main subject in the middle phase with mine. One of these days I'll figure out how to use something off center in that softer darker area.

Nigels
3-Dec-2008, 08:15
Apologies if this is too obvious. You didn't say whether you constructed the pinhole yourself. If you did remember to make the pinhole conical and not cylindrical.