Originally posted by maltfalc . . .a front and rear component . . .
The rear component's the
habitual, consistent, repetitious position of the camera at the same place for each shot - a position defined 'rear aperture' if you will. The front component's the 'frame' of the transparent 'front sight'. Many athletic skills rely on this same factor.
As for 'calibration', lacking a better word at the moment, I simply refer to the very obvious need to outline the lens' approximate field of view for a given FL. Let the precision with which this is accomplished suit the actual need in practice. (Such a
slap-dashery approach ain't for everyone.)
I've used this sort of pseudo-OVF, open-aperture gun sights, TLR sports finders and wire view frames on Speed Graphics with equally satisfactory results long enough to be willing to publicly suggest them to others who might be interested them. The '
MacGyver-factor' at work if nothing else.
If they don't "make sense" to you I apologize for not expressing the idea(s) in a manner that you can understand. Perhaps you'd like to construct one of these and review your results here? Maybe one for each of the four image ratios available in the Q's which are otherwise unavailable at any cost, much less virtually for free?