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Hi Peter.
To work out your exposure time without star trails divide 700 by your FL when shooting at around 0 deg dec and 1000 close to the pole.
So at 18mm you could have gone around 35 sec (if you can do that on your camera). For 50mm around 15 sec. Some will say you can only divide 500 by the focal length. If you are doing large format then maybe but for what you are doing 700 will not be a problem.
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