Wide open does not usually pose a problem with telephoto lenses.
Aberrations are often common with wide-angle lenses and those are not the
football and blue halo exhibited here, but darkening in the corners
(vignetting) and/or gull-shaped stars out towards the edges. My 135mm/f2.8
Zuiko is perfect for astrophotos wide open. I'm not sure why, but I think
it was just a bad lens!?
The caption with the picture on pg.226 said that it was with a 50mm lens
and that this is common with lenses below 90mm- so it shouldn't happen with
a 180mm. Vignetting is also shown in the lower photo on page 227.
Rob
>
>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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