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Help with GT81 + M63 Rotator + Flat 6aii Reducer

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#1 erictheastrojunkie

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Posted 14 January 2020 - 03:36 PM

So I picked up a GT81 with a M63 rotator which threads onto the back of the focuser, the Flat 6aii, I'm guessing, can thread onto the back of the M63 rotator. What effect will this have on spacing requirements (if any), I think I have the spacing for the Flat6aii adjustment through my sensor figured out, just need to test it. I'm just not sure how the rotator thickness needs to be accounted for. As of right now I'm going to go off this diagram, which includes a distance from the back of the telescope (before the focuser) to the image sensor, 166.7mm:

post-277380-0-41468700-1542600369.jpg

From the 166.7 I'll subtract the width of the rotator, the Flat 6aii with the correct adjustment, spacers, filterwheel, and finally the camera, then adjust the focuser to make up the difference. Does that make sense?


Edited by erictheastrojunkie, 14 January 2020 - 03:36 PM.


#2 OldManSky

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Posted 14 January 2020 - 05:26 PM

No effect of any kind.  The spacing only matters *after* the flattener -- not before.  The distance from the back of the flattener to the image plane remains the same.  The location of the focus point stays the same.

 

I will warn you that adding the rotator (which I've also added on my two WO refractors) may bring the focus point to where there isn't a whole lot of drawtube sticking out when you're in focus.  There's plenty (about 15mm in both my cases) for autofocus to work, etc., but it's pretty close in.  The good news is, that means there's less drawtube "hanging out" unsupported, so less likelihood of focuser sag smile.gif


Edited by OldManSky, 14 January 2020 - 05:28 PM.


#3 erictheastrojunkie

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Posted 14 January 2020 - 06:35 PM

Good to hear, I'll have to test it out with my ZWO EAF, 15mm should be plenty. 



#4 pawelpiechnik

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Posted 16 May 2020 - 03:54 PM

How did it work, @erictheastrojunkie ?




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