[rollei_list] Re: couple of ignorant lens design questions.

Hi Dennis,

> Date: Thu, 10 May 2007 13:05:02 -0400 (EDT)
> From: dpurdy@xxxxxxxxxxxxxxx
>
> Stupid question #2  Is contrast always good in lens performance?  Or
> is there some way of designing shadow detail into a lens?  Or if one
> lens gets better shadow detail than another lens of the same focal
> length and speed and size then the one with more shadow detail is
> really just getting a boost from flare.  And that extra shadow detail
> should always be of low contrast.
>
You've gotten some excellent responses to your other questions, so I
thought I'd add some thoughts on #2. I approach this from a user's
standpoint and will leave it up to those folks who understand lens design
to supply the technical aspects.

My two 35mm systems are good examples of this parameter. The Olympus OM
lenses have very "flat" or evenly distributed MTF curves, and exhibit
noticeably lower contrast than my Leica Reflex lenses. I think this is a
design trade-off, as a consequence that I've noticed in lenses with high
contrast and "lumpy" MTF curves such as the Leica, Zeiss and Schneider
optics is that the contrast and color performance varies noticeably with
changes in aperture. I have not noticed any greater tendencies of the OM
lenses to flare, so that leads me to suspect that their lower contrast is
due to lens materials and/or coatings.

As to whether contrast is always good, I'd think that depends on the
users' intentions. For technical work, I find the OM lenses to be superior
because of their flat MTF curves; when changing apertures, only the DOF
varies, making it easier to match shots in varied lighting conditions.
OTOH, they don't come close to the expressiveness or "pop" of the Leica,
Zeiss or Schneider lenses for landscapes or portraiture.

Regards,

Neil





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