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Re: [OM] 180mm/f2.8 Zuiko dog

Subject: Re: [OM] 180mm/f2.8 Zuiko dog
From: Tomoko Yamamoto <tomokoy@xxxxxxxxx>
Date: Fri, 06 Feb 1998 16:50:08 -0800
Cc: a0011306@xxxxxxxxxxx
At 01:10 PM 2/6/98 -0700, Garth Wood wrote:
>At 10:19 AM 2/6/98 -0500, Rob Roy wrote:
>>>Last week a friend showed me his newly acquired 180mm/f2.8 Zuiko which he
>>>had purchased for just over $300 CDN (~$200US).  From the outside the lens
>>>was like new.  I was envious that I hadn't been in the camera store first.
>>>
>>>Last night he showed me some astrophotos he had taken before he took the
>>>lens back to the store.  I have never seen anything like them.  The stars
>>>were football-shaped (astigmatism) and the brighter ones had blue halos
>>>around them (chromatic aberration).  Any ideas as to what is going on?  I
>>>have never even heard of such a bad lens!?
>
>Tomoko Yamamoto (another contributor to this list) suggested that your
>exposure time may have been too long.  Anything longer than about 20-30
>seconds, at any reasonable magnification, will not show the stars as point
>sources but as "doughnuts," and even longer exposure times will show a
>distinct arc line.  Unless your buddy was using a tracking rig, long
>exposures will produce such problems.  I'm at a loss about the chromatic
>aberration, though, if it *was* that.
>
Although I am no expert of astrophotography, the blue halos reminded me to
have a look at two astrophotographs Jim Lumley (in the US) of this list
sent me.  His photograph of stars does show blue halos around bright stars
and around one particularly bright star has a bluish circle of 4 cm in
diameter.

I am sending a cc of this to him to get him to comment on the effect.




Tomoko Yamamoto
Photographer, Composer, Soprano
mailto:tomokoy@xxxxxxxxx
http://www.charm.net/~tomokoy/
-All the photos (except panorama) with OM's-
http://ep.com/ep/csp.html?csp=1130
-Olympus Equipment Classifieds-

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