Originally Posted by

**DWThomas**
OK, I ran through some numbers ...

Typically a focal length equal to the diagonal of the film frame is provides a "normal" lens field of view.

Using the square root of the height squared plus width squared for a 6 x 7 frame comes out to about 9.3 cm = 93 mm for the frame diagonal dimension. The angle of view is about 53º.

Going into Pinhole Designer with a focal (pinhole to film distance) length of 93 mm, using 1.9, Rayleigh's constant, in the calculation, I get a pinhole diameter of 0.43 mm, which results in an effective aperture of f216.

If I use the constant of 1.6, which some folks use, I get a pinhole of 0.36 mm for f258...