>At 10:19 06/02/98 -0500, you 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!?
>>
>>Rob Roy
>>
Have a look in "The Backyard Astronomer's Guide" by Terence Dickinson and
Alan Dyer, page 226. There is a fine example of two astrophotographs, one
taken at f1.4, the other at f2. The first one shows aberrations all over
the place. The second one (i.e. stopped down at f2) is MUCH better. Both
were 30-second exposure (that's right, no time compensation).
I know it might be self-defeating to buy a 180mm f2.8 and use it at f4,
but tell your friend to check out the reference and to give it a try. If
there is no defect with that particular lens, you might be happily
surprised with the results...
Keep us informed!
)))) Daniel Biron
)))) Montreal QC Canada
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