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22454Re: [William Optics] RE: GTF81 focal length

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  • Dan Kordella
    Oct 13, 2013
      Thanks - so I know I'm not crazy :)

      I ended up returning the scope. I bought it because of the additional flattener. It seems kind of absurd to add a focal reducer/flattener to a scope that already has the flattener built in. I hope WO gets this thing worked out because it really is a beautifully made scope. I know of a couple other people that have returned this scope very soon after buying it. 

      I ended up going with an Explore Scientific 80mm instead...

      Dan


      On Sat, Oct 12, 2013 at 10:12 PM, <sberrada99@...> wrote:
       

      Yes you are correct

      I get 553mm using single sub measured from astrometry.net

      That is quite a difference to F6.8 vs F5.9 



      ---In William-Optics@yahoogroups.com, <william-optics@yahoogroups.com> wrote:

      Hello - I'm new to the group here. 

      I've been an enthusiastic amateur for a long time, but in the past year and a half have become an addicted astrophotographer and have gone as "all-in" as my budget will allow. 

      I recently purchased a GTF81 from Agena to be my main imaging scope, to go with my Atik 383l+ monochrome camera.

      While the scope is beautifully made (I have never owned a scope with this caliber of craftsmanship), I have gotten some odd results from imaging that concern me.

      I use Ron Wodalski's CCD calculator and figured that based on the stated specs of the telescope (478mm focal length, f/5.9 optics) I should get an image scale of about 2.33 arcsec/pixel.

      I've done some imaging, and immediately noticed that not only is it a bit more challenging to guide this telescope because of the weight, my images seemed to have been a bit grainier, as if the signal-to-noise ratio isn't great (up until recently I had been using a Stellarvue scope working at f/5.6 - should not be a dramatic difference to f/5.9!). 

      When I plate-solve my images, I find I get an image scale of 2.05 arcsec/pixel, which corresponds to ~550 mm focal length and f/6.7!

      Has anyone else gotten similarly odd results with this scope? 

      Thanks,

      Dan 


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