Diagonal of 135 is 43.2mm.
Diagonal of 8x10 is 305mm.
300/305 = 0.9836
0.9836 x 43.2 = 42.49mm
Can't get more precise than that unless you measure the aperture opening of a specific 135 camera and of a specific 8x10 film holder. But DF is right... if you crop 135 to 8x10 that changes the formula.
Diagonal of cropped 135 is 38.4mm.
0.9836 x 38.4 = 37.8mm
So a 35mm lens on a cropped 135 image (24x30mm) is closest to matching a normal (305mm) 8x10 lens and is even closer matching FOV of a 300mm.
Last edited by Mike1234; 11-17-2009 at 08:57 AM. Click to view previous post history.