Olaf,
taking stars pictures with only a tripod and a B exposure is easy, with
pretty good results. The only problem is that stars apparently move so if
you don't want to see lines insted of points you have to limit the duration
of exposure: roughly 10 seconds with a 50mm (or 5 seconds with a 100mm, 20
seconds with a 24mm). This time depends also on the region on the sky and
will increase moving from the equatorial zone to the polar one (of the
sky), so as Richard mentioned it is better to use a faster film (800/1600
ASA) in order to fully utilize so a short exposure: I must say that with a
dark sky, a 135/2.8 (zuiko, of course!) with a Scotch 800-3200 developped
at 1600 ASA and exposures ranging in 5-10 minutes I took several pictures
without having a "washed" sky. With a non very dark sky the exposure have
to be limited, but you should try.
As to use the lens at full aperture or stopped-down, I use them at full
aperture for sky photos. The lens will perform better stopped down (a
couple of stops) in terms of sharpness, contrast and vignetting, but for
every stop you have to double the exposure, not taking in account the
reciprocity problem. Since I have a telescope but not the motor, I take
photos moving the telescope manually, so every minute gained is good. In
any case, the only situation for non using the lens at full aperture is
when in that situation it performs bad.
According to the published features of ProviaF, it seems me one of the best
film in terms of reciprocity defect, since it does not need a compensation
for exposure up to 2 minutes (if I remember correct): a very long time.
Try.... and enjoy!
Ralf Loi
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