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22507RE: Re: [William Optics] RE: GTF81 focal length

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  • timm_bottoni
    Dec 11, 2013
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      Hi Doug,

      Yes, the effective focal ratio is actually F/7.68 with a focal length of 783mm.   The optical triplet is the same in both the GT102 and GTF102, but the GTF102 has the built in flattener which actually adds to the focal length.

      I'm not familiar with the camera you have, but I have a Canon 60D (unmodified) and I tried some Andromeda shots in September that didn't turn out that good due to my light pollution, but it looks like it fits corner to corner.  If I can get out now that it's much higher in the sky I will try again.  We've have really bad weather here in Chicago so far this Winter, so I haven't been out in over a month.


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