[Leica] Lens evaluations

[Erwin Puts <imxputs@knoware.nl>]

>You know, that I truelly respect and appriciate your opinion, Erwin.
>I'm just asking myself: If the physical parameters support one side,
>and the emotional view supports another side - isn't the test missing
>something essential which is vivid to human perception ?
>

The interesting topic, inaugurated by Alf, about the alleged differences
between   the human perception and the physical test parameters, has been
extensively discussed by Zeiss engineers since the introduction of the
lenses for the Contax RTS.
(BTW: a more captivating topic than the question who is the photojournalist
with the most professional experience or if a dealer has lived up to
consumer expectations.)
This topic got additional relevance as the Contax series of lenses was a
momentous departure from the lens design philosophy of the redoubtable
Contarex series of lenses, still called by many the lens range yet to be
surpassed.
The new lenses for the Contax were the result of a fresh look at those
physical parameters within lens design that really could have direct
relevance for the human perception of optical qualities.
So it had been noted that microcontrast around 10 lp/mm had the most impact
on the perception of sharp subject outlines and added to the general
impression of briliance in a picture. It was also noted that a very high
resolution in fact detracted from the perception of image clarity and the
clear rendition of fine details, including subtle gradations in small
object areas. Again the fine delineation of subject matter in strong
highlights and deep shadows adds to the impact of a picture. But these
aspects can not be captured by notions as resolution, bokeh or whatever.
We see the same evolution of qualifications in the car industry. Topspeed
and horsepower give way to roadholding and safety and the car design goes
to proactive engineering. Where the older cars just were brutish boytoys.
So in lens design the shift in design takes into account modern emulsions
and better understanding of the visual perception.
So the real dichotomy is not "some essentialia that are vivid to human
perception" versus "physical parameters".It is the "modern definition of
image quality (where notions of point spread functions, spatial frequency
and optical transfer functions ride high)" versus the classical definition
of image quality (where notions as bokeh, resolution are predominant).
There is a different kind of discussion here, Just as with cars, any person
may speak fondly about his old Chevy or Volvo and be of the opinion that
driving this car gives more satisfaction and pleasure than driving a new
Honda.
No dispute whatsoever. Everyone has his/her emotional attachments. Stating
that these old cars have better engineering or are a better embodiment of
the concept of the automobile would be debatable.
The same line of argument works for lenses. There is a certain satisfaction
in looking at and appreciating the image quality of a Summarit or Summar or
even a  second generation 28mm.
But again: these lenses have been designed with the older notions of image
quality. One can admire it no doubt. The new generation of lenses is better
not only along measurable dimensions but also along visual perception
dimensions. Any trained and educated eye can see it. You need to relearn
old notions and habits of looking at images.
This is a fascinating subject and these lines above are just the start of
an emerging field.
It are these discussions on the LUG that forces me to rethink my own ideas
and find better ways of expressing them.
Erwin