Originally Posted by
Ted R
The primary variable is focal length. The diagonal for whole plate is about 10 inches so the standard lens is about 10 inches focal length. For portraits a lens having one and a half to two times the diagonal is sometimes preferred, this gives 15 inches and 20 inches, these are approximate values, some people prefer the perspective given by an even longer lens, say 24 or 30 inches. Now you need some bellows extension!
The second variable is the aperture, the size of the hole. An f4 lens gives shorter exposure times than an f8 lens (four times shorter) but the f4 lens is much bigger and heavier and usually more expensive. An f4 lens is easier to focus because the image is brighter on the ground glass. The f4 lens has shallower depth of field (nose out of focus, eyes in focus) than the f8 lens.
I would place brass finish secondary in importance to finding the appropriate focal length and aperture.
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