I need help understanding this! I trust & recommend Mark Hansen, but can't figure out what he's saying about 75 & 80mm screens. I don't understand how one screen can have a different focal length than another.
On another thread, Dan D. said what I thought was true:
"The surface a screen rests against in a removable-screen Rollei like an E3 is the same surface where the focusing happens. So no matter how thick the screen, the focus surface will always be in the same place, meaning no need for adjustment....
"Most TLRs, like older Rolleis, Autocords, Yashica-Mats, have the focus screen's top surface index its location. So different thicknesses of screens will locate the focusing surface at different levels."
If this is so, then on any Rollei with a removable hood, why would there be a difference between a 75mm screen & an 80mm screen, if they're resting in the same place?
Bill Maxwell asks you to order your screen for either the fixed or the removable viewfinder. I always thought this was because they're different-sized rectangles, &/or different in thickness, & had to be put in with the right side up. But am I to believe the focal lengths of the screens are different? In what sense does Mark mean that screens have different focal lengths – or is it just a difference in the height at which their focusing surface is positioned in the body?
If all fixed-hood Rolleis had 75mm lenses prior to the introduction of 2.8 lenses, & all had the same design for focusing screens, then the only models in which there could be a difference between 75 & 80mm screens would be the 2.8s with fixed hoods – that is, the 2.8A-B-C-D-E1. For E2-E3-F with either 75mm f3.5 or 80mm f2.8, No Problem?
Kirk
PS: I should add that for me, this is a very practical question. Mark is working on a couple of Rolleis for me now. One is a 'beater' 2.8C (with fixed hood) that I wanted to try because its Xenotar lens has 10 aperture blades, & supposedly nicer bokeh. I sent along a replacement screen of the fixed-hood type. So I wonder if this would become one of the mis-matched 80mm lenses with a 75mm focusing screen??
PPS on Ljos' point: I have Maxwell screens, both plain & split-image. IMO the latter are a mistake – definitely harder to focus accurately.