[Leica] Retrofocus Lens Quality?

[Mike Johnston <70007.3477@compuserve.com>]

To:      INTERNET:leica-users@mejac.palo-alto.ca.us
Subject: [Leica] Retrofocus Lens Quality?

Marc Small wrote >>>Well, you are wrong.  It is an optical fact, not marketer's
hype, that a retrofocus lens is harder to design to perform identically with a
non-retrofocus lens.  By requiring the lens be retrofocus, as SLR's do, is an
additional parameter the optical designer has to work around.<<<

 I'm not either wrong, because my point was that the presence or absence of one
theoretical parameter cannot be generalized to predict the performance of any
particular lens. Lens designers have _hundreds_ of parameters and conjugates to
choose from--all of which are overshadowed, in consumer lenses, by the two main
limitations, which are physical size and the target selling price.* Just
because it is "easier" to design a non-retrofocus lens does *not* mean that all
non-retrofocus WA lenses are superior to all retrofocus WA lenses. It's just
not that simple. 
 And as it happens, there are several specific properties which non-retrofocus
WAs are easier to correct for--linear distortion principally. However, they
inherently show more perspective distortion and more cos4 falloff than
retrofocus designs. So exactly what are you looking for? Given the long
experience that designers now have with retrofocus designs and the glasses now
available, it is possible for a lens designer to accomplish a very good
retrofocus design that will outperform--actually, not theoretically--many good
non-retrofocus designs. Saying that a particular lens can't be better than a
good symmetrical design because of some general rule you read in a book, is
(sorry) to believe marketing BS. Given enough relaxation of the two principal
limitations mentioned above, an extreme wide-angle retrofocus lens could be
designed which outperforms _every single_ camera lens now available on the
consumer market...if, for example, you could postulate selling it for $250,000
like a satellite lens, or $70,000 like a U lens for a stepper device. So if you
want to believe that non-retrofocus designs are easier to optimize, fine, but
if you want to extropolate from that that all non-retrofocus designs _have
been_ optimized to be superior, well, as I say, go get yourself one of the
legion of nifty non-retrofocus WA point-and-shoots and have a nice day.

 --Mike Johnston, chief editor, _PHOTO Techniques_ magazine, Niles, IL

* From a Zeiss White Paper on lens design:
 A camera lens is a well-thought-out balance of many factors...these factors
include: cost, size, weight, mechanical robustness, optical tolerances,
mechanical tolerances, speed, focal length, basic type, resolution, contrast,
chromatic correction, distortion, flatness of field, vignetting, flare, color
rendition, reliability, long-life performance, maunufacturability, thermal
stability, and many others. Between all these factors exist many complex
relations....

P.S. Anybody know if Fred Hess actually got a dozen R8 motor winders? If so, he
could probably set up a nice little side-business here on the LUG as a
motor-winder reseller...kinda like scalping Super Bowl tickets....<g>