Re: R6 and R7

[Eric Welch <ewelch@gp.magick.net>]

Marc James Small wrote:

>claimed credit for changing Leica's design practices to comply with Zeiss's
>by using MTF data as the determiner of lens quality rather than Leica's
> former practice of using "final image quality" as the arbiter.  

First of all, years before this claim this guy changed the way Leica 
evaluates lenses the book "Leica Lens Practice" talked about how Leica 
used MTF and other tests (one they call OTF which they say is more 
advanced than MTF) to help them design lenses. They claimed that MTF was 
the best in the 60s (or was it 70s). Contrast and resolution back in the 
40s and 50s were adequate for lens design. Later OTF. So who's right 
here? Your interpretation of a person's presentation to the LHSA, or a 
book that very comprehensively talks about Leica's design philosophy 
over the years? And what do you think they used to determine final 
optical image quality? Off film? 

> Eric deniees vehemently, pointedly, and repeatedly that Leica used residual
> aberrations.  However, the documentation on this is pretty immense, 

That is purely false. It depends on what you mean by used. Claiming 
Leica introduces "spherical aberration" (one particular type of 
aberration) to get the "Leica glow" is a whole lot different than 
claiming minimizing and balancing the inherant aberrations in a lens in 
a way that optimizes a lens's performance. It's two different birds 
here. Leica allows a bit of curvature of field with some lenses (like 
the 400 6.8 telyt and some of the high speed lenses like the Noctilux), 
for example, because by doing so they can enhance the contrast 
significantly. 

> analysis.  The point's not worth hammering away at:  if Eric wants to
> believe Leitz long used MTF criteria to design their lenses, so be it. 

You ought to know what you are talking about before making claims. Leica 
said they used MTF. Not for the "final determinant" in a lens' quality. 
Have you even heard of OTF? Have you ever read "Leica Lens Practice?"

> folks at Wetzlar and, later, at Solms were unaware of this, but Eric might be right.

Your sarcasm is hardly appropriate, or appreciated.

> some years thereafter.  Gianni Rogliatti drew my attention to this -- and to
> the retention of aberrations by Leica, as well as to their use of a "final
> image quality" standard -- in private correspondence several years ago;  his
> knowledge derived from his frequent visits to Wetzlar and Solms and
> discussions with K D Schaefer and others at the plant.

You ignore that fact that ALL LENS MANUFACTURERS do this. Contrary to 
the claim of one camera dealer in Edmonton, Alberta, that I ran into 
once, even Contax lenses have aberrations. He tried to tell me the 
Contax 60 2.8 macro had "no aberrations." What makes you think that 
Leica is different in this case than any other manufacturer? Sure, the 
way they determine final image quality of a particular lens is done 
differently than any other manufacturer. Lets get all the facts out 
before trying to destroy my credibility, or twisting the things said by 
others.

-- 
Eric Welch
Grants Pass, OR