[Leica] 60/2.8 Macro question

["Anderson, Ferrel E" <AndersonF@ria.army.mil>]

On 8 July Don J. questioned whether I meant line pair per mm or lines per
millimeter resolution in my comments on the performance of the  60 and 100
APO lenses.  Although I stated 80 line pairs per mm resolution, I meant to
state lines per mm resolution.  Thanks for the question Don.

I want to point out that 80 lpmm equates to the "finest" level of detail in
xxxxxx's lens reports.  "Finest" relates to mtf  performance at 40 lppmm,
which is equivalent to 80 lpmm..

In years past I tested my 50 Summicron-R and 90 Elmarit-R lenses, and the 50
f1.4 Nikor, with Kodak High Contrast Copy film and H&W Control Developer
with  NBS resolution test targets at 76 focal lengths.  At this distance,
the maximum resolution the test procedure could record is 240 lpmm.  I felt
that this maximum resolution limit would exceed the resolution ability of
any lens I would want to test, but I was wrong.  The Summicron exceeded 240
lpmm at f4 in the center of the field!  The Elmarit was not far behind, with
optimum performance around 200 lpmm at f4 across the field.  The Nikor
performed very well also, and recorded 160 lpmm across the field at its
optimum aperture; however, its contrast was not up to that of the Leica
lenses.  This data was the optimum with compensation for field curvature,
which was slight.    I examined the negatives with a high quality
microscope.

To determine the practical value of this kind of resolution in printing with
my Focomat 1C enlarger and Focotar f4.5 lens, I examined  the projected
image of the negative taken with the Summicron at f4 with an Omega grain
magnifier.  I could just barely make out the 240  lpmm image with the
enlarger head at the top of the column and the Focotar at f4.5 (a
testimonial to the quality of the Focotar).  My conclusion was that this
kind of resolution could only be taken advantage of with very large
enlargements, and would be very hard to achieve with the limitations of even
minor vibrations and focus errors.  Even resolution of 80 lpmm is in excess
of what is required for an 8
x print.  56 lpmm would result in excellent prints up to 8X.   Prints
confirmed my visual impressions.