My direct experience with the Zuiko 180mm lens is null; my remarks are a
summarization of those of others from the astrophotographers list. Please take
this accordingly.
The f/2.0 version of the 180 is reported to have outstanding focus of all
colors at the film plane and crisp resolution all the way to the corners of the
frame. Therefore, star images, which are always a point source, are round and
consistent in color. On the other hand, the f/2.8 version reportedly does not
focus blue wavelengths as preceisely, resulting in a blueish, fuzzy fringe
around stars. This effect is especially pronounced near the outer edges of the
frame leading some to speculate this lens also has some coma or other optical
abberation.
This is possibly the result of one bad experience getting distorted out of
proportion or is indeed representative of this specific lens. I do know from
experience that a lens that is an outstanding performer in "earth-bound"
photography does not necessarily perform well in astro work. The demands
placed on optical and mechanical systems for astro imaging are different,
requiring a different set of design compromises for optimal results. FWIW
John P
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