Quote:
Originally Posted by tah997
Yeah 10sec was probably a little too long.
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Tim, there is the "Rule of 600". This says you should divide 600 by the focal length of your lens to get the maximum exposure time before stars start to trail. If you do not have a full frame camera you need to apply the crop factor to the focal length.
So on a full frame like the Canon 5D MkII, 600/100 would give you 6 seconds. A 550d with its 36/22.3=1.6 crop would give 600/(100*1.6) or 3.7 seconds which you could round off to 4.
The numbers are affected by the pixel size, but this is a reasonable approximation.