[Leica] On-film resolution (if it is X lp/mm, what size letters should I be able to read with a magnifier?)

[krieger at usc.edu (Martin Krieger)]

If I use a 22x magnifier to examine optically printed 4x6 prints, I can see
the granularity fairly well. I'd like some guidance then:

What is the size of the "granules" or grain-clumps on the film?
If I use a 22x magnifier (or whatever you use), given that I can discern
some letters or numbers, what minimum lp/mm might I conclude.

Why do I want this. Some of my work is a survey of neighborhoods. If I want
to be sure of the address of a place, I will try to discern its number from
the image. Of course I am far enourgh away, so that the number is small on
the negative. I need some idea of what kind of limits there are to this
process, given reasonable demands on my holding the camera, etc. I might
need only 20% (I don't know, maybe it is 40%) on the MTF to do the
discernment, so this is not so demanding a task.

If you know, please let me know. If you have an idea where I can find out,
let me know where to go look. Obviously the spy satellite people have this
down to a science. I just don't know where to look.

Thank you,
Martin Krieger
krieger@usc.edu