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From: jlg@lanl.ARPA
Newsgroups: net.rec.photo
Subject: Re: Dingy colors...bad lens?
Message-ID: <15526@lanl.ARPA>
Date: Fri, 2-Nov-84 15:18:37 EST
Article-I.D.: lanl.15526
Posted: Fri Nov  2 15:18:37 1984
Date-Received: Sat, 3-Nov-84 21:55:17 EST
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Organization: Los Alamos National Laboratory
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> I have been having problems with the performance of one of my camera
> lenses.  I have a Sigma 28-80mm zoom lens for a Pentax ME Super.  I have
> noticed that it consistently yields "dingier" pictures than my other
> lenses (Pentax 50mm or Kiron 70-210mm zoom).  By "dingier", I mean that
> the overall picture is darker and certain colors do not reproduce well.
> For example, a yellow-gold color comes out gold-brown.

Have the aperature linkage in the lense mount checked.  This sounds like
consistant underexposure to me.  Actually a simple check for this would 
be to purposely overexpose with this lense.  Try several different
exposures from (say) one to for stops overexposed and see which come out
best.  If this is the problem, tell your camera repair shop that the 
lense is consistantly underexposing by 'n' stops.  He should be able to 
work from there.  

I can't offhand think of anything else that would cause this problem.
I guess it could be an obstruction in the lense, or a flaw in the
optics not caught be quality control.  Any optics experts out there 
think of other causes?