[Leica] DR contrast

[sethrosner at nycap.rr.com (Seth Rosner)]

Scanning the batched conversations I came across this one that caught my eye
and about which I have some significant knowledge. Some on the list may
recall my writings in LHSA's Viewfinder magazine several years ago
contradicting Erwin Puts' statements about the series of 50/2 Summicrons.
One of them even resulted in marc small accusing me of libel and predicting
that Erwin would sue me. Poor lawyering on marc's part as truth is an
absolute defense to a defamation action.  ;-)

 

My purpose here is to dispel a very widely held opinion that the 1956
DR/Rigid 50 Summicron is a low-contrast lens. It is not, except when
compared to the latest Leica and other lenses at wider apertures. Ten years
ago I had correspondence with Lothar Koelsch, then head of lens design at
Leica, about this very issue and received from him print-outs that I have in
my hands as I write, of the MTF curves calculated by Leitz/Leica Camera, for
the 50/2 lenses from the Summitar through the DR/Rigid, 11817 (1969) and the
1979 version that I believe is still current. 

 

Bear in mind that every lens is a compromise, that there is no such thing as
a perfect lens. If there were, such a lens would perform flawlessly at full
aperture and as a photographer stopped down, the image would degrade
progressively because of diffraction! So the designer has to decide in which
direction he/she wishes to correct for most, since one cannot correct all
aberrations simultaneously. The DR/Rigid concedes some softening contrast at
f/2 and 2,8 in order to correct more highly for spherical and chromatic
aberrations and thus achieve significantly higher resolution. Geoffrey
Crawley, then Editor-in-chief of the British Journal of Photography,
confirmed to me in our correspondence in the late 1960's, that due in some
significant part to the emphasis put upon contrast by the great Japanese
manufacturers, principally Nikon and Canon, that seemed to have persuaded a
large number of photojournalists to favor highest possible contrast (keep in
mind that most of these folks did then and still do tend to shoot wide open
most often, eh Tina & Ted?), Leitz designed the 1969 50 Summicron #11817,
for max performance at f/2. And wide open, looking at the MTF charts, no
question the contrast of 11817, especially at the lower spatial frequencies
- 5, 10 & 20 line pairs/mm is significantly better than the DR. At f/2,8 it
is better than the DR but only on axis; at the near and far edges the DR's
contrast is superior and at f/4 and 5,6 it is markedly superior, again
except directly on axis. As to the current 50 Summicron, contrast is
somewhat superior at the first three stops whilst the resolution of the DR
at medium apertures is better than both later Summicrons. 

 

>From Leica's own  MTF charts it is clear that the myth of the DR/Rigid lens
being soft and low-contrast is just that - a myth. Use that lens at f/5,6 &
f/8 and even at f/4, and you have an extraordinary image-maker. And using a
rigid 50 on an M8 as I do is even better, since it eliminates the outside
quarter of the image circle wherein lies the vast majority of the design's
"softness".

 

Just my 2c.

 

Seth