Re: [APML]: Guiding Error Question

[charles@jon.cjfny.org]

AS>> Does anyone know the maximum error (in seconds) before stars appear
AS>> elongated on film for various focal lengths? I'm interested specifically
AS>> in 300mm and 180mm.

AS>It's difficult to give an exact answer to this question because it depends
AS>on what is the smallest star diameter that those lenses can deliver. It
AS>also depends on how many times during the exposure you exceed the tolerance.

AS>I can tell you what an absolutely safe number would be based on 12um stars...
AS>4126/FL (mm) = Star size in arcseconds for 20um stars and 12um stars would
AS>be 60% of that.

AS>(4126/300)*.6 = 8.25"

AS>(4126/180)*.6 = 13.8"

AS>You need to guide to at least half the size of the smallest stars to
AS>be sure they are round so you're looking at 4 and 7 arcseconds respectively.

AS>Chuck  <aa6g@aa6g.org>


This is very surprising. I thought the tolerances would be much less
stringent than that! I know that I can confine my guding to the inner
circle and not get any trailing with my 180mm. That circle appears to be
about 35" in diameter through my 4-inch scope. Why the discrepancy?

Charles