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Digital Pinhole

Borrowing a table from Pinhole Math:

Format Focal Length Ideal Pinhole Neg Diagonal Lines/negative f-stop
35mm 22 0.171 43 1257 128
6x7 42 0.236 90 1907 177
4x5 74 0.314 154 2452 235
5x7 100 0.365 210 2877 273
8x10 150 0.447 308 3445 335

We see that the smaller the format, the smaller the lines/negative or resolution of the resulting pinhole image. This is the reason that most pinholers like to use 6x7 and larger sized negatives. 4x5 is often seen as the ideal pinhole format size.

Here is what happens if we keep following the above table down to the smaller sized digital sensors:

Format Focal Length Ideal Pinhole Neg Diagonal Lines/negative f-stop
35mm 22 0.171 43 1257 128
APS-H 17.2 0.151 34.4 1136 114
APS-C 14.2 0.137 28.3 1031 103
4/3 10.8 0.120 21.6 901 90
1/1.7 4.8 0.080 9.5 597 60

1/1.8

4.5 0.077 8.9 579 58
1/2.5 3.6 0.069 7.2 519 52

Compare the 4/3 Olympus sensor with the 4x5 sheet film (thet sensor on your phone is near the very bottom of this table). To get the same field of view on the 4/3 system you need a 10.8 mm focal length. Not going to happen with a DSLR. Just might be able to do it with the micro 4/3 that has no mirror to get in the way. But look at the resolution loss: 901 vs. 2452. For the digital you are at 37% of the resolution of the larger system. Maybe this is worth it for convenience and portability, but you have alread lost so much with going pinhole itself. It is possible, using a great APO lens on a 4x5 and the right film to get 200 line pairs per mm resolution. Multipy 154 x 200 and you get 30,800 lines of resolution. Pinhole is less than one tenth of what a lens can do and digital cuts that down even further.

Does this rule out ever using digital pinhole then? Of course not. Just know what you are sacrificing for convenience sake. If your sensor is good enough to handle the low light of a pinhole image and still able to do high def video, you might really have something to play with. A mouse view of the world could be fascinating.

 

Chris Patton, cpatton@stanford.edu