hi all the most common private msg i get on sgl is,"how many seconds should i take ?" well basic wide field shots just on a tripod with no motors, piggy back or just stuck on a camera tripod its easy lets say you have a 28mm lens on the camera and lets say you want to do a basic wide field shot of ursa major.

so you shoot for 45secs and stars trail doh!

try this, the magic number is 600 :)

so i no my camera as a 28mm lense attached but not sure how long to keep the shutter open before trails apear

divide 600 by the lense of 28mm

600 divided by 28 = 21.4 seconds

so lets round that of to say 21 secs and there you go

no i hear you say i can not set to 21 secs most dslrs will shoot at 20 secs so use that always go lower, never higher

a was in my local one night and a old drunk bloke told me that a took it with a pinch a salt tried it the next night worked a treat every time we see the old boy in the pub i always buy him a pint

so divide 600 with the lens size now if you have say a 70mm lens, 600 divided by 70 = 8.5,you will get a time before trails of 8.5 secs so the bigger the lens the less time to keep the shutter open,the smaller the lens the longer you can keep the shutter open more time

cheers pat

clear skies always