In article <35365AF5.73AB@hotmail.com>, fw007@hotmail.com says...

>My Nikkor manual focus 50mm f1.8 lens when shot at f1.8 AND focused at
>infinity gives a very soft picture, with noticeable vignetting. Stopping
>down one stop the image becomes sharp. Is it usual for lens' shot at
>widest aperture AND focused at infinity to give soft images ? I hesitate
>to use the word out of focus, it just doesn't look sharp, kind of what
>you get using an instamatic maybe a smidge worse. Anyone out there with
>experience re this problem. Is it a design issue or a manufacturing
>fault. I have a 100mm Nikon series E and I feel it is one of the
>sharpest lens' even when shot wide open at f2.8 focused at infinity.

Since your 100mm E is sharp at f2.8 (and that is one VERY sharp lens,
a real sleeper! ;-), the issue of focus error is unlikely to be relevant.
The E-Series 50mm f1.8 lenses (same optics as the late compact AIS
and the AF 50mm f1.8's) do vary some from sample to sample, but
most are reasonably good at f1.8, though the corners are sometimes
noticeably less sharp as the center wide open (the corners are good
even at f1.8 in the best samples). It is normal to see moderate
illumination corner roll-off wide open with most short FL lenses.
I would try other samples, if you want a good 50mm f1.8 E-Series lens
(these are delightfully compact and light, free of linear distortion,
and they generally are sharp lenses).
David Ruether
http://www.fcinet.com/ruether