I've always found the OM-1n perfect for astrophotography and I know many
amateur and professional astronomer friends who also have. I think it
especially excels at piggyback photography. Never tried an OM-2 though.
Hope someone teaches me how to calculate exact exposure time if I measure
the degrees of the star trails.
Fernando
A quick formula for calculating the exposure time BEFORE stars trail is
500/f (f = focal length of the lens). This formula is a version I
modified from Covington's book after some experimenting. As for
calculating the exposure time from a star trail. If the earth rotates
360 degrees in 24 hours (for quick calculations sake we'll ignore that
it is slightly quicker than this!) then it rotates 15 degrees in 1 hour
and 0.25 degrees in 1 minute. If you use a reference point in the sky
and inculde it on the film, say using Betelguese and Rigel or some other
bright object, and knowing their angular distance you will be able to
apply an absolute scale to the exposure. Knowing this scale and that
0.25 degrees of a star trail is equal to 1 minute of time then you can
easily calculate the exposure time. Hope this helps.
All the best,
Gareth.
--
Gareth.J.Martin
Research Postgraduate
School of Geographical Sciences
University of Bristol
University Road
Bristol
BS8 1SS
g.j.martin@xxxxxxxxxxxxx
attackwarningred@xxxxxxxxxxx
eclipsing.binary@xxxxxxxxxxxxx
NE NLCOG - The amateur NLC observing group:
http://freespace.virgin.net/eclipsing.binary
"The only way of discovering the limits of the possible
is to venture a little way past them into the impossible."
Arthur C. Clarke's Second Law.
"There is hopeful symbolism in the fact that flags do not
wave in a vacuum."
Arthur C. Clarke
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