Re: Crayford style focuser for Vario-Finder 10x60 ; 61x250 f/4.1


Roland Christen
 

Piggyback on rings is not recommended for such a long heavy main scope.

Rolando



-----Original Message-----
From: M Hambrick <mhambrick563@...>
To: main@ap-gto.groups.io
Sent: Sat, Oct 17, 2020 9:45 pm
Subject: Re: [ap-gto] Crayford style focuser for Vario-Finder 10x60 ; 61x250 f/4.1

Thanks Bryan Those are very useful formulas.

So if I plug my equipment specifications into the formulas I have:
GP = 7.4 microns (SBIG STi or ST2000-XM)
GF = 480 mm (This is my Tele-Vue Pronto that I currently use for guiding. It is piggybacked on top of the 180 EDT rings)
IP = 6 microns (SBIG STXL16200)
IF = 1166.4 mm (180 F9 EDT with 0.72X Quad TCC)

Guider focal length > 0.2*(7.4/6.0)*1166.4 = 287.7 mm

This would suggest that the 250 mm focal length of the 10 X 60 Vario-Finder is not long enough to use as a guide scope for the 180 EDT. So this raises yet another question; Which is the least bad option; The 250 mm Vario Finder mounted directly on the main imaging scope, or the 480 mm Pronto piggybacked on the rings of the 180 EDT ?

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