From: ka1gt@cbnewsm.cb.att.com (robert.m.atkins)
Subject: Re: Resolution of Lens ???
Organization: AT&T
Distribution: na
Date: Fri, 20 Nov 1992 00:34:20 GMT

In article <1992Nov19.214725.7999@craycos.com>, sog@craycos.com (Steve Gombosi) writes:
> 
[lots of stuff on resolution deleted]

> Maybe I don't understand how this all works, but aren't the resolutions
> of the lens, film, and system (lens *and* film) related in this way:
> 
> 	1/Rs = 1/Rl + 1/Rf
> 

Yes, there is an empirical relationship of that form which is often used.
I've never seen a derivation for it, but I'm prepared to believe it gives
a reasonable approximation.

> If that's true, and Rs = 100lp/mm and Rf = 320 lp/mm (for Tech Pan),
> that means that your lens has to resolve better than 145 lp/mm.
> 
> That ain't too shabby.

Actually its pretty bad. Depending on exactly what you define as resolution,
a diffraction limited lens should resolve close to 1800/f-stop lp/mm. Lets
be conservative and say only 1200/f-stop. That means a diffraction limited
lens at f4 should resolve 300+ lp/mm, similarly 428 lp/mm at f2.8 or
215 lp/mm at f5.6. I know this is conservative since I can see a resolution
of over 250 lp/mm from an f5 lens I have when looking at the aerial image
(the formula would say 240 lp/mm).

> 
> What does Kodak claim for TMX resolution?
> 
> Isn't it around 160 lp/mm?

Kodak rate T-MAX 100 at 200 lp/mm (high contrast)

> If so, then your lens has to resolve 267 lp/mm to get 100 lp/mm
> reolution on the final negative. I don't think you're doing 
> anything wrong - I think you're a victim of algebra.
> 

Well, if we believe Kodak at 320 lp/mm for Tech Pan (HC-110 dilution D
development - which is what I use) then there should be no problem at
all in getting 100 lp/mm. You would only need 145 lp/mm from the lens
as you said. This should be easy, yet modern photography had GREAT
trouble with the best lenses available. If you look at most of their
tests lenses tended to top out at about only 70 lp/mm (though I never
found a reference to exactly how they did their testing on on what type
of film).

My guess is that the discrepancy lies in the term "resolution" (which
is somewhat subjective when determined by eye) and perhaps in the
"optimistic" resolving power numbers from film manufacturers. Perhaps
the resolving power of Tech Pan depends critically not only on the film
itself, but also on the developer, time, temperature, agitation, ISO
rating and other conditions. I've used all the data given in the Kodak
data sheets to try to optimise things, but maybe I'm missing something.

A couple of other points come to mind. (1) At the resolution limit the
image of the test target is no longer high contrast (the aerial image
that is). The resolving power of Tech Pan is only 125 lp/mm for low
contrast targets (usually 1:1.6?). Thus as you approach the resolving
limit of the lens, the resolving power of the film itself drops also.
Thus if the lens JUST resolved 400 lp/mm in a low contrast aerial
image, 125 lp/mm from the film would give only 95lp/mm on the negative.

(2) Test targets of the "black and white bar" variety have a square
wave intensity distribution and thus contain a significant amount of
3rd harmonic content (i.e. contain spatial frequencies 3 times that of
the fundemental). If Kodak use such targets to get their resolving power
then there is no problem. If they use sinusoidal targets, or (incorrectly)
calculate lp/mm from other (MTF) data then the numbers might be
inconsistant.

===============================================================
Bob Atkins  AT&T Bell Labs  email (direct)  att!clockwise!rma
===============================================================
Newsgroups: rec.photo