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From: ark@alice.UUCP (Andrew Koenig)
Newsgroups: net.rec.photo
Subject: Re: Nikkor 200mm f4 MICRO problem
Message-ID: <3576@alice.UUCP>
Date: Mon, 15-Apr-85 15:01:34 EST
Article-I.D.: alice.3576
Posted: Mon Apr 15 15:01:34 1985
Date-Received: Tue, 16-Apr-85 01:13:09 EST
References: <433@tekchips.UUCP>
Organization: Bell Labs, Murray Hill
Lines: 27

J. Eric Roskos complains about a 200mm f/4 micro lens
that gives slides with dark corners as f/4, and progressively
less so at smaller apertures.

This phenomenon is called vignetting, and virtually all lenses
have it to some degree, regardless of manufacturer.

The design of any lens is a trade-off among a number of factors,
including sharpness, contrast, vignetting, size, price, and so on.
A good designer will optimize a lens for the conditions in which
it is most likely to be used.


Macro lenses are usually used to take close-ups.  Long macro
lenses must be stopped far down to get any depth of field to
speak of.  Thus I would expect such a lens to be optimized for
sharpness over a wide distance range, especially at small
apertures.  I would not expect vignetting at wide apertures
to be high on the list of priorities.

Incidentally, does your lens accept 52mm filters?  It is virtually
impossible to design a 200mm f/4 lens that takes 52mm filters
without some vignetting.  200 divided by 4 is 50.  Think about it.

Photographing a subject in the center of the frame with a background
of solid color and intensity on slide film is probably the most
severe imaginable test of a lens's vignetting.