Re: 5% MTF "contrast" (TECH-3D digest 217)

[T3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxx>]

RE: John Orht tells John. B about 5% contrast and 120 lpm resolution. 
This reminded me that the English language edition of Leica 
Fotographie (5/96 E) has on page 44 & 45 a related discussion. I 
can't quote the whole thing because of copyright, but can mention a 
few lines as a critique if the article.
"Lenses and Image Quality II" is title
 "In part one I said a lens must be capable of imaging 60-80 lpm
(on film rlh) if it is to record human hairs in a portrait."  (Rule 
of thumb?)
 MTF chart redition on paper assumed to be 100% contrast..imaging 
blends flare of white into black to reduce contrast, severe at fine 
spacing.
"The higher the MTF curves lie in the graph, the better the lens is 
likely to be. In the case of a direct comparison, an increase of 
contrast of 2.5% at a resolution of 5 lines/mm is already visible, 
alternatively, 10% in the case of 20 lines/mm. The contrast at 5 and 
10 lines/mm describe the 'brilliance' of an image. Values below this 
indicate softness or even flare.  The contrast at 20 and 40 lines/mm 
indicate the fineness of structures rendered. Examples are human 
hair, plumage of birds or filagree structures in leaves and flowers."
Quotes from Lothar Koelsch, Head of Optical R&D Department Leica Gmbh.
Article has some spot diagrams too and mentions their use!
BobH


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