Archived posting to the Leica Users Group, 2000/03/19

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Subject: [Leica] apo 90 versus 4/150
From: Mike Johnston <michaeljohnston@ameritech.net>
Date: Sun, 19 Mar 2000 16:20:38 +0000

>I'm sympathetic to the temptation to compare things like MTF
>percentages and extropolate out to what "should be" the case, but >it
amounts to wishful thinking--more careful research than that is
>required to find the truth. There is more to "print quality" than
>lp/mm.

Mark R: >>>My language may be weak but this language is thoughtlessly
demeaning and insensitive.<<<


Well, I certainly didn't intend it to be insulting, and I'm sorry if it
sounded that way. I meant what I said. I really am sympathetic to the
temptation to extropolate such things as system resolution, for
instance, mathematically instead of by trial. But I've come to believe
that it's seldom a valid approach--I think there are too many variables
that impinge on actual printmaking for the mathematical modeling to be
consistently valid.

Note that I didn't say that MTF data is invalid--I merely said that
starting with this data and extropolating what "should" happen in a
print based on this data is a wrongheaded approach--and I believe it is.

Believe me, I've been over this territory many times with our
contributors who write on system resolution and related topics--who are
in various cases engineers, mathematicians or physicists, or lens
designers.

If you like, I can reference a list of articles we've published over the
years that address this subject. I don't agree with all of the authors'
conclusions (nor would they all agree with me), but the discussions are
illuminating.

- --Mike