Harry Callahan
Member
It'll affect sharpness a little. Not as much as you may think, though. There's basically just a very limited focus shift that in many cases drops away against effects like depth of field - and user variability. I've tried red-scaling film on occasion; sharpness turned out OK. Keep in mind it's only something like 110um shift on the focal plane.
I have been thinking of a 1/10 of a mm deviation and from a technical view at least this should be off a lot. When a lens is collimated, i think it`s done down to a few um. Also i have an old camera where the pressure plate offers pretty exactly 0.1mm deviation - and as the old lens does not produce as much DOF, focus is off by like 10ft. When focusing at about 50ft and aperture around f11.
Close-up range should be even worse.
You can always compensate for this effect by turning the focus ring a few hundredth of a degree away from infinity. Jokes aside, people who shot red scale rarely care about sharpness. If anything critical sharpness is detrimental to "the look".
I'm aware... in fact i once had a camera where the lens wasn`t collimated properly or the groundglass got out off alignment - and i did just that. After focusing on the glass i always turned the focusing ring for about 1mm - and it worked.
But i see that people doing red scale don`t care about sharpness in the first place - this technical aspect just gotten into my mind and as no-one had mentioned it before...