Archived posting to the Leica Users Group, 1998/11/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Nathan Schneider has a useful and succinct discussion of optical quality measures on their website. The paper addresses your questions directly, I believe. It's at www.schneideroptics.com/quality/quality.html. Dick Chandler .>From: Nathan Wajsman <nathan.wajsman@euronet.be> >Subject: [Leica] Reading MTF charts > >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