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As has already been said, very impressive, but for people who have
limited maths skills here is a list of the max. exposure times for a
number of focal lengths that will not show star trailing at various
declinations. The focal lengths are strange numbers as they are
converted from 35mm film figures. Just use the number nearest to
your lens.
Focal length Degrees of Declination of Object
0 40 60 80
12mm 25 33 50 144 seconds
15 21 27 41 120
17 19 23 36 103
22 14 19 29 82
31 10 13 20 58
53 6 8 12 34
62 5 7 10 30
84 4 5 7 21
125 2.5 3 5 14
185 1.7 2.1 3 10
250 1.2 1.6 2.5 7
310 1.0 1.3 2.0 6
470 0.7 0.9 1.3 4
625 0.5 0.7 1.0 3
935 0.3 0.4 0.7 1.9
1250 0.2 0.3 0.5 1.4
I hope these figures are of use to someone.
raymo
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