Archived posting to the Leica Users Group, 2003/05/17
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At 7:16 PM -0400 5/17/03, Don Dory wrote:
>Phong,
>I was implying that if an element was moved out of it's designated location
>+/-0.003 then bad things happen to the light. The designs coming out of
>Solms are fabulous, but there are continuing occasional tales of really bad
>results, sometimes flare, sometimes severe vignetting, sometimes not as
>crisp as supposed to be. The only logical conclusions would be either an
>element out of spec or an element out of place.
>
>The +/- comes from one of Erwins bulletins when he was talking about the new
>retro 50 and how it conforms to muck tighter specs than the other 50
>Summicrons he has tested recently.
>
>Thanks for reading.
>
>Don
>dorysrus@mindspring.com
As I have stated numerous times, vignetting by the lens is not a QC
issue, but is an intrinsic part of the lens design and construction.
+/-0.003 anything except meters or leagues will have no effect.
Decentering, which I assume you refer to, has serious effects on a
number of aberrations but not vignetting. Besides, centering has
generally been one of the strong suites of Leica, and they continue
to be at the forefront in this regard. The QC problems relating to
missed edge blacking and other things has nothing to do with this.
As someone else has pointed out, if Y.Li has consistently greater
light falloff on one side of the frame than the other, he has a
shutter, not a lens problem.
If the images are sharp, and from what Y.Li has written this seems to
be the case, decentering is not an issue. The issue is that he, and
seemingly others on this list do not understand what parameters are
affected by the intrinsic optical designs that Leica employs for
their wideangles, namely standard or very slightly retrofocus
construction versus the exteme retrofocus construction used by
designers of SLR lenses. Different people have different expectations
of a lens, and will put up with or vilify a lens for different
properties. I hate distortion; Y. Li seems to hate any vignetting. I
can easily fix vignetting in printing or with a center filter, but
cannot reasonably fix distortion, so my criteria are plain.
Again, read my previous posts on this topic.
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* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com
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