4x5 pinhole camera exposuregreenspun.com : LUSENET : Large format photography : One Thread
I'm putting together a pinhole camera by replacing the lens board of my 5x4 with a milled piece of 1mm thick aluminium. The pinhole will be exactly 1/100 of an inch. Other than trial an error, how do I calculate exposure times, etc? One application involves using it in a room lit with flourescent light. Any help appreciated.
-- c skiscim (firstname.lastname@example.org), January 24, 2002
The book, 'The A-Z of Creative Photography' by Lee Frost has a full chapter on Pinhole Photography. It has a section on Calculating the pinholes F/number and Exposure factors. Harry
-- Harry Martin (email@example.com), January 24, 2002.
Check out "How to Calculate Exposure Times" at.....
-- R.L.(Mac) McDonald (firstname.lastname@example.org), January 24, 2002.
Many references off this article: http://www.luminous-landscape/pinhole.htm As far as exposure goes, trial and error ain't bad-I recommend in this one case TMax 100 for its great reciprocity characteristics.
-- David Stein (DFStein@mac.com), January 24, 2002.
This might help you: http://www.mrpinhole.com/calcpinh.html
If you drill the pinhole through the 1mm aluminum you are going to have a problem. The material is too thick and you will have a pin tunnel instead a pinhole which will degrade your image. Find some thin brass shim stock to drill the hole into. You can then just fasten that piece of brass over the hole of an extra lensboard. Remember that there is an optimum hole to film distance for each hole diameter.
-- Wayne Firth (email@example.com), January 24, 2002.
As Wayne mentioned the material is way too thick - look for 1-2 mil brass shim stock. The 1mm thicknes of the aluminum will allow all sorts of diffraction/reflection effects, along with cutting the field of view down - unless you are using an exceptionally long focal length it wouldn't even cover 4x5.
-- Wayne DeWitt (firstname.lastname@example.org), January 24, 2002.
For some reason I'm having trouble getting a message up, so excuse me if a couple are accidentally posted.
A pinhole of 0.01" - is pretty small for a 4x5 - that size hole would be optimal at 25mm focal length!
There is a good online calculator at http://www.mrpinhole.com/calcpinh.html
As others have pointed out, 1mm is way too thick - you need to have the material as thin as possible to avoid the problems mentioned. I have had good luck with the pinholes purchased from Lenox Laser (http://www.lenoxlaser.com)
These are laser-drilled in 0.0005" S.S. and are mounted to steel disks that can be attached to a larger plate or lensboard.
Also, on a bellows camera, you will need to somehow mark the focal length on the camera that corresponds to the pinhole size, so that you can lock it down at the appropriate distance for the pinhole.
-- Matt O. (email@example.com), January 24, 2002.
Your f-stop will be the focal length divided by the diameter of the pinhole. So, if you have a focal length of 2.5 inches and a pinhole of .01 inch, your f-stop will be f/250. I would like to point out that 1 mm is too thick for a proper pinhole. I use brass shim stock 5/1000'ths of an inch thick for making pinholes. See my article How to Make a Pinhole.
I have designed a handy pinhole exposure calculator that you can print from my site. Mount it on matt board, or laminate it in plastic. Go to Unblinking Eye, click on the "Articles" button, then go to the bottom of the page and click on the article entitled "Exposure Calculator for Pinhole Exposures".
Since you are using 4x5, you might also be interested in my article on how to make a 4x5 pinhole camera from a coffee can. The nice thing about the curved film plane is that it gives zero distortion in the horizontal plane and a very wide angle field of view. Mine has a "focal length" of about 52mm and takes great photographs. See Coffee Can Pinhole Camera.
-- Ed Buffaloe (firstname.lastname@example.org), January 25, 2002.