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Old 12-06-2010, 09:23 AM
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mldee (Mike)
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How effective are SCT 6.3 Frame reducers?

I have now got my equipment setup as I want it, and am moving on to alignment mode.

I wish to use my C8 in both long 2000mm/f10 FL, and short 1200mm/f6.3 using a Field Reducer/Flattener, with my QHY8.

After going through a series of "what is the correct sensor to FR spacing" exercises, I think I have correct numbers now, thanks to IIS contributors and AgenaAstro.

I am putting the FR right at the scope visual back, followed by a Meade 1209 remote microfocuser, then the QHY8 with a 2" to T adaptor nose screwed into the existing camera T nose. The 2" section allows me to move the camera to trial various distances, as well as giving a firm mount. Spacing from the rear shoulder of the FR to the CCD sensor can easily be varied from about 78mm to well over 110.

Initial trials show lots of "space invaders" and eggies around the edges, basically pointing in a circular direction. Unprocessed pic attached. 10x2 minutes taken with PHD guiding on EQ6, which I suspect has excessive backlash, too.

My question: How much edge distortion should I expect at optimal spacing with a 6.3FR? I have both an Antares (220mm FL, spacing 81mm) and a Meade (FL=154/260mm, spacing to sensor: 57/105mm) according to the experts, post-2006 Meades are 154mm FL, but I'll try both settings. Both reducers were bought new this year from Agena.

I have done an initial star collimation on the C8, but I'm also not putting poor collimation out of the equation at this time. Still a lot of variables to take care of, that's why my question is: Just how good a picture at the edges should I be able to expect with a C8 and 6.3FR on a QHY8? I don't want to spend weeks trying to achieve the impossible, just the achievable
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Last edited by mldee; 15-06-2010 at 09:55 AM.
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  #2  
Old 13-06-2010, 01:27 PM
gbeal
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Quite honestly don't know, but from what you post here it isn't too far away? Have you trialed the varying distances, quite small differences too? I got the feeling from your post description you were able to slip the nosepiece in and out a tad, so maybe get accurate with just where exactly the nosepiece is and go from there, I reckon it will all be trial and error. A good full moon project.
Gary
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Old 14-06-2010, 08:16 PM
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mldee (Mike)
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Hi Gary,

I think I'm being a bit hasty in suspecting the FR's, as I tried the C8 direct last night on the same stars and the distortions were still there, so I have either a collimation or focus or both as first suspects.

I have just swapped out the C8 for a different scope so will verify the mount and camera that way. If that looks OK, I'll go back to the plain C8 and start fiddling. A clear sky would help at the moment.

Cheers,
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Old 16-06-2010, 06:16 PM
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peeb61 (Paul)
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Hi Mike,
I had the same problem as you using my f6.3 focal reducer on my Meade 10" LX200gps using my Canon 350D. I have fiddled with the spacing and found the nearest setting for my setup was around 105mm. I think you may find that all focal reducers are not created equal eg focal length so it's trial and error.

Hope this helps.
Paul

Last edited by peeb61; 17-06-2010 at 02:08 PM.
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Old 17-06-2010, 01:26 PM
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Astrobserver99 (Rob)
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I use the following on my C8:

2" SCT adapter -f/6.3 FR -T adapter - Camera

The Antares 2" SCT T-adapter is OK

No adjustment necesssary...
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