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> I just bought a Nikon FM2, that came with a Nikon f/1.8 50mm AF
>lens. (Why does an AF lens come with a manual camera?).
The newer version works fine as a MF lens, and it is good, and cheap.
>I've taken several shots of the comet over the past week.
>Although the images came out really well, this lens does not
>have a flat field at all - the stars in the corners of the frames are
>severely flared. The comet tail extends across the entire frame,
>so I can't crop out the distorted star 'points'. I don't remember
>having this problem with my Nikkor-S f/1.4 50mm that I used with
>my Nikon F years ago for astro photos. I obviously need a lens that
>has a relatively flat field when the aperture is wide open, because
>astro photos take long exposures as it is. Have Nikon lenses gone
>that far downhill?
No - at wide apertures, the 50mm f1.8 Nikkors should easily surpass
an early version of the f1.4. The f1.8's are quite flat-field, also,
and normally have good center-to-corner uniformity in performance, even at wide apertures. I suspect that your lens is defective (it happens, even with Nikkors, which is why I always check lenses that I buy, and return any that are not up to par).
Hope This Helps