Nicely done Steven. Good pickup for 20 sec.
Hi Matt, divide 700 by the focal length of the lens/scope. That will give you the number of second you can go for without trailing near 0° Dec. Nearer the pole divide 1000 by the focal length. There's some complicated formula that will work it out for each degree dec but the 700 and 1000 rule and estimated in between works pretty well.