From: Bjorn Rorslett
Newsgroups: rec.photo.equipment.35mm
Subject: Re: Nikon AF20-35 F2.8 D
Date: Sun, 06 Apr 1997 08:58:00 +0100
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References: <3345EC7D.333C@datacomm.ch> <33467D84.145F@mindspring.com> <334694BC.5EC9@foto.no> <3346EA0F.3416@hol.gr> <5i79p5$k28@newsstand.cit.cornell.edu>
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To: Bob Neuman

Bob Neuman wrote:
>
> Hmmm, unless the lens has some seriously decentered elements, I would
> not expect performance inferior at f11-22 to that provided by another
> similarly high-quality lens. A really poor lens could be worse at these
> stops, but it would be worse yet at wider apertures... Smaller stops are
> the great lens-levelers, since diffraction degradation is the same for all
> lenses for a given format at the same small stops. There may be some
> differences in corner performance even at small stops with super-wides
> and wide-angle zooms, but I would expect most of the frame to look pretty
> much similar in good lenses by f16, anyway...
> Hope This Helps (If all goes well, "HTH" and "Bob Neuman" will
> become "David Ruether" - with the advent of
> a web page and a new e-mail account...;-)

It is colour aberration, the achilles heel of wide-angle zoom lenses
that comes into play here. Many modern designs, including the 20-35
f/2.8 Nikkor which used for photojournalism at fairly large apertures is
an extremely good lens, have sacrificed off-axis colour correction in
order to solve other optical problems. It is all a matter of computer
optimising criteria, I think.

The reason why 20-35 f/2.8 cannot match the old 25-50 f/4 for landscape
photography is quite simple: At f/11-f/22, settings that are
indispensable for landscape photography use, colour fringing in the DOF
zone makes the image perceptably fuzzy. This effect can be clearly seen
in the corners and using a good 20X loupe, also near the axis. I like to
stress this results from the lens design and not from a poor sample of
the 20-35 f/2.8. Each and every one of these lenses I have tried
exhibits the same pattern of colour aberration. The old 25-50 f/4,
whilst not coming up to the sharpness of 20-35 f/2.8 on-axis, is not
troubled with colour aberration and this is evident in landscape
photography when the old lens gives high-contrast, high-definition
images at f/11-f/22. These are lenses with different designs and
therefore, giving different photographic results.

Finally, I would like to challenge the statement that lenses poor at
small apertures would be worse yet at larger apertures. This simply
isn't true. Take a 200 f/2 Nikkor as a good example. This lens performs
magnificently wide open and down to f/5.6. Beyond f/5.6, its optical
quality declines rapidly and at f/22, it's nearly unuseable. The same
relationship holds for the Nikkors 300 f/2, 300/2.8, 400/3.5 and 600/4,
all of which I own and have tested in depth.

regards/bjorn