Archived posting to the Leica Users Group, 2003/05/18
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Hi Henning,
Look at any interior design magazine or architecture. The best
shots are large format. Now digital too. For large format black
and white prints you can pas on the center filter and adjust in
the darkroom. I had a 121 SA w/cf, but never really got a
chance to use it without a studio setup. Big flash is what
it takes to allow for the decreased f/stops with the center
filter. There's a great book out called The Photographer's
Assistant' which shows what a current studio is like.
Cheers,
Henning Wulff wrote:
> At 7:59 PM -0400 5/17/03, Don Dory wrote:
> >Henning,
> >I was mostly thinking of one of the aspheric elements forward or backward in
> >space. Perhaps I am naive, but I think up to two stops vignetting in the
> >corners doesn't bother most people. What was described was a severe hot
> >spot in the center of the image. I don't think that even an unpainted
> >portion of the lens barrel could cause a hot spot in the center; such a hot
> >spot would move around the frame depending on where the source of light was
> >coming from.
> >
> >One of my underlying assumptions in this whole discussion was that the
> >original complaint was a real visible problem. Over the years, I have
> >gradually realized that there is usually some basis of fact to reported
> >problems. There is, of course, the occasional troll that throws gasoline on
> >a lighted match. That is usually pretty rare.
> >
> >Don
> >dorysrus@mindspring.com
>
> Don,
>
> The displacement of any element in _any_ direction will first be
> noticed in a loss of resolution and an increase in aberrations. If
> the displacement is axial, the effect will of course be symmetrical
> while radial displacement will produce non-symmetrical deterioration.
> Either type of displacement will produce very severe degradation well
> before the slightest effect of increased vignetting is seen.
>
> I don't think the post was a troll; rather a misunderstanding of the
> design aim point and the resultant performance parameters.
>
> I have noticed before that people coming from SLR's have different
> expectations of optical performance than those used to RF cameras,
> just as many cannot get used to the coincidence type rangefinders
> coming from AF SLR's. It can be difficult getting used to the
> different handling, just as the performance parameters of lenses of
> different construction can seem weird.
>
> My 21/2.8 ASPH, while having less vignetting (talking about optical
> vignetting due to lens design rather than physical vignetting due to
> mount or element diameter limitations) than the SA 21/3.4, still has
> more light falloff than any recent good Nikon, Canon or whatever
> 20/2.8. It is noticeable if you look for it, or if you are sensitive
> to it. Conversely, in all other respects it is a far superior lens
> then those same Nikon, Canon or whatever.
>
> The 21/2.8 ASPH is a very mild retrofocus design, constructed that
> way so that metering is possible with the M5,6,7 cameras. This helps
> the vignetting over that of the 21/3.4, but the strongly retrofocus
> 20/2.8 lenses for SLR's are better. There are a few tricks that are
> used to expand the exit pupil size at larger angles so that light
> falloff is less than demanded by cos^4, but at the present stage of
> development, to maintain the best overall performance within a given
> degree of retrofocus ratio will mean that there is more falloff with
> RF wideangle lenses than SLR lenses.
>
> The highest level of performance can still be achieved by using a
> nearly symmetrical construction, and letting light falloff be as it
> may. To compensate for this, a center filter is then used. This cures
> all the problems except price, size and lens speed. Performance will
> be stellar, as exhibited by modern LF designs.
>
> You can't have it all.
>
> --
> * Henning J. Wulff
> /|\ Wulff Photography & Design
> /###\ mailto:henningw@archiphoto.com
> |[ ]| http://www.archiphoto.com
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