Archived posting to the Leica Users Group, 1998/11/16

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Subject: [Leica] Reading MTF charts
From: Nathan Wajsman <nathan.wajsman@euronet.be>
Date: Tue, 17 Nov 1998 08:05:28 +0100

All this talk about whether Kodachrome or Fuji Velvia is best and how to
evaluate them, especially Erwin's last post with the conclusion "MTF
charts are the way", inspired me to grab a couple of data sheets and
look at the MTF charts. But I must confess ignorance in not knowing how
to interpret the curves. What does the "spatial frequency" on the
horizontal axis mean? Is it simply lines per mm? And what is special
about the number 20 that Leica lenses are calibrated to? On the vertical
axis we have some percentages. For instance, in the curve for Fuji
Provia (and Sensia) I see that for a spatial frequency of 20 the
corresponding percentage is about 70%. What does this mean? I have some
vague idea that a higher % is better, but what does this imply for
ordinary usage? And finally, I see that for spatial frequencies lower
than 10 the percentage is above 100%. Why?

Thanks in advance for enlightening me.

Nathan

- --
Nathan Wajsman
Overijse, Belgium

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