[Leica] Resolution vs. Contrast?

[Peter Klein <pklein@2alpha.net>]

Folks:  I'm currently comparing two older 85-90mm lenses, both 
approximately f/2.  To avoid prejudicing the discussion, I'm not going to 
reveal what brand(s) they are.

I shot the "newspaper taped to the wall" test with each.  This means 
shooting a double-page spread of the stock market quotes, with the camera 
on a tripod, placed so the newspaper just fills the frame horizontally.  I 
shot Kodachrome 64 at all stops, and viewed the slides with a portable 30x 
hand microscope.  Please note that I'm taking some real pictures with the 
lenses, too, but that roll isn't finished yet.

All this is crude, but it does give a reasonable idea of how each lens 
performs at that distance. The lower-case letters in a stock market quote 
are about 1mm high, and you can see three distinct lines in them (such as 
in the letter "e"). Reduce a 68 cm-wide double-page spread down to a 36 
mm-wide frame, a factor of 18.9, and these three lines in a mm-high letter 
reduce to less than .0175 mm each on film.

I encountered an interesting difference between the two lenses.  Wide open, 
lens #1 shows the smallest print quite blurred.  But I can tell that the 
characters are letters and numbers, and sometimes identify one.  However, 
the lines of the characters are very light and somewhat irregular in how 
dark they are.  In other words, the appearance of the print is very low 
contrast.

With Lens #2, wide open, the text is completely unreadable.  The space 
within individual characters seems almost completely filled in, such that a 
small "e" looks like a dot and a capital "E" looks like a rectangle.  But, 
though the characters are blurred beyond recognition, the outer edges of 
the characters are distinct, and the contrast between a character and the 
space around it is much more distinct than Lens #1.  In other words, Lens 
#2's image appears to be of lower resolution, but higher contrast.

Both lenses seem to have about equal resolving power at f/5.6 and narrower, 
but Lens #2 continues to have the appearance of better contrast at these 
openings.  Oddly, at a couple of stops in this range, both lenses show 
slightly more readable characters near the *edges* of the slide than in the 
center!

Now the fun part--which lens do you think might take better pictures 
(especially wide open), and why?  I'm curious how this crude but easily 
done test translates to "look."

- --Peter