Determining exposures for the pinhole camera

Brian Young shows us how to measure our exposure times for our pinhole cameras a little more precisely than “bright sun” or “hazy sun”.

Writer and photography / Brian Young


Introduction to exposure times for pinhole cameras

The purpose of this short article is to encourage pinholers to adopt an objective means of determining the long exposures required for pinhole cameras. The subjective “bright sun, hazy sun” approach is all very well but it lacks rigor.
The method is based on extrapolation of the familiar EV Chart (see below). Imagine this chart being extended downwards for ever-increasing f-numbers and to the left for ever-increasing exposure times until we are in a region of interest to pinholers.

EV chart exposure and exposure times for pinhole camerasThe EV Chart was conceived for use with lensed cameras which may be set to a variety of f-numbers. With a pinhole camera, the f-number is fixed and this introduces a major simplification which makes the task of extrapolation much easier. Instead of a 2-dimensional EV Chart for a particular film sensitivity, we have 1-dimensional EV Line.
Extrapolation works for any negative as long as reciprocity holds. Fortunately, in the author’s experience, film or paper sensitivities of ISO 25 or less do not appear to exhibit reciprocity failure, even for exposures of several minutes.

The Exposure Table

An Exposure Table will be found at the end of this article. Here there are exposures (in seconds) for a typical paper negative with a sensitivity of ISO 12.5. Across the top of the table are a range of f-numbers (N) in half-stop intervals from 45 to 1024. Down the left-hand side are exposure values (EV) from 7 to 16 in steps of 0.5. You are free to interpolate if your f-number doesn’t happen to be one of those shown.

"Am Knieproderstrasse" by Brian Young. exposure times for pinhole cameras
“Am Knieproderstrasse” by Brian Young. This picture was shot with my Black Box camera (f = 175mm, d = 0.5mm, N = 350) on Adox Pan 25 ISO 4in x 5in cut film. EV was 13.5 and exposure was 42s.

Thanks to the assumption of reciprocity, the table can be used for other film or paper sensitivities. For example, some papers have a sensitivity around ISO 6 (one stop down from 12.5) so you will double the time shown. My favourite 4in x 5in cut film has an ISO of 25 (one stop up from 12.5) so I will halve the time. If you use ISO 100, then divide the time shown on the table by eight.

Finding the EV

If you have a light meter, well and good, since they measure EV directly. Just make sure that you set the film speed to 100 ASA or ISO. You can often find good light meters in flea markets; don’t buy a Russian one since they use the GOST standard.

A conventional camera may also be used as a light meter. Set the ISO to 100 and read off the aperture and shutter-speed readings. Then enter the EV Chart for ISO 100 (above) to find EV for the scene.

Set your camera to show half-stops in aperture and/or shutter speed and you will end up with half-stops for EV, which is fine. Some cameras offer an option of one- or two-thirds stop intervals which should be declined.

I do hope that you find the EV approach to exposure useful and rewarding. Happy pinholing!

Exposures (in seconds) for 12.5 ISO paper negatives
  f-number in half-stop intervals
EV 45 54 64 76 91 108 128 152 181 215 256 304 362 431 512 609 724 861 1024
7.0 128 181 256 362 512 724 1024                        
7.5 91 128 181 256 362 512 724 1024                      
8.0 64 91 128 181 256 362 512 724 1024                    
8.5 45 64 91 128 181 256 362 512 724 1024                  
9.0 32 45 64 91 128 181 256 362 512 724 1024                
9.5 23 32 45 64 91 128 181 256 362 512 724 1024              
10.0 16 23 32 45 64 91 128 181 256 362 512 724 1024            
10.5 11 16 23 32 45 64 91 128 181 256 362 512 724 1024          
11.0 8 11 16 23 32 45 64 91 128 181 256 362 512 724 1024        
11.5 6 8 11 16 23 32 45 64 91 128 181 256 362 512 724 1024      
12.0 4 6 8 11 16 23 32 45 64 91 128 181 256 362 512 724 1024    
12.5 3 4 6 8 11 16 23 32 45 64 91 128 181 256 362 512 724 1024  
13.0 2 3 4 6 8 11 16 23 32 45 64 91 128 181 256 362 512 724 1024
13.5 1 2 3 4 6 8 11 16 23 32 45 64 91 128 181 256 362 512 724
14.0   1 2 3 4 6 8 11 16 23 32 45 64 91 128 181 256 362 512
14.5     1 2 3 4 6 8 11 16 23 32 45 64 91 128 181 256 362
15.0       1 2 3 4 6 8 11 16 23 32 45 64 91 128 181 256
15.5         1 2 3 4 6 8 11 16 23 32 45 64 91 128 181
16.0           1 2 3 4 6 8 11 16 23 32 45 64 91 128

Formerly an academic engineer and originally from London, Brian now lives in Berlin where he practices, researches and writes about alternative processes, pinholing and traditional film photography.

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