Roger, just out of curiosity I plugged in the subject distance and subject size numbers into the
required focal length calculator over on Cambridge in Colour. Here's what I got:
Fixed parameters:
Subject Distance = 4 feet
Subject Size = 18x27 inches (my estimate for the typical 'frame' of a head and shoulders portrait at that distance)
Variable parameter, and calculated required focal length:
35mm -> 60mm
6x6 -> 98mm
6x7 -> 112mm
4x5in -> 190mm
8x10in -> 329mm
These are the focal lengths required for each format to photograph an 18x27 inch subject at a distance of 4 feet, i.e. same camera position.
Assuming the same aperture is used on each format, why would you need to work at a greater camera to subject distance with 8x10 using a normal 300mm lens? Wouldn't field of view and dof be identical to using a 60mm lens on 35mm film?
Am I missing something?
Cheers,
Lynn