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Message: <blockquote data-quote="Binastro" data-source="post: 3569563" data-attributes="member: 111403">Thank you very much Ron.For astro scopes the easiest method for me is the star drift method.Using a star on the celestial equator, such as Orion belt stars, if the time to drift from one side of the field to the other, with the star crossing the centre field as nearly as possible, takes 4 minutes then the field size is 1.003 degrees. Say 1 degree. The mount has to be very steady.For spotting scopes this is a bit tedious as a 2 degree field takes about 8 minutes.For a 7.5 degree binocular field, very tedious, about 30 minutes. Like watching paint dry, especially if the star misses the centre of the field. And binocular tripods move.As you say a set up indoors has much more control.Why are field size measures useful?I suspect that Leica's figure might be wrong, so measuring it will give a correct value.For me most useful.I saw a satellite pass fairly near Jupiter using the Canon 18x50.I was able to give an accurate estimate of its closest angular distance from Jupiter timed by radio controlled clock to 3 second accuracy.My astro satellite specialist was able to tell me that it was an obscure rocket stage with full details.</blockquote>