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Can I determine optimal corrector spacing on my Newt using refocused star method?

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#1 John Tucker

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Posted 09 October 2019 - 04:33 PM

Having a little trouble getting the corrector to sensor distance correct for my TS "PowerNewt" with the 0.75 ASA corrector/reducer and non-reducing TS "Superflat" corrector I bought out of concern that F2.8 would prove to difficult. Both give a little more coma in the corners than I'd expect and small changes in the spacing around the recommended values don't seem to help.

To facilitate comparisons between pictures with different spacing I've been slightly defocussing to make the little "O"s in a manner analogous to collimating on a star, but it occured to me I have no idea whether there is theoretical support for this. I have noticed that if the scope is collinated, I get nice symmetrical O's in the middle irrespective of spacing. The O's are fat on the center most part of the circle if the spacing is very short and toward the outer part of the circle if the spacing is very wide.

Does this make sense? Based on my results so far I'm about to spend $30 and $45 shipping for a 3mm extension ring only available from Germany.

Edited by John Tucker, 09 October 2019 - 04:34 PM.


#2 Alex McConahay

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Posted 09 October 2019 - 07:03 PM

Don't know about the first question (how to figure the distance).

 

You may be able to avoid that big expense by hitting your local Ace hardware and looking for some form of nylon gasket or ring with appropriate thickness, and just screw the devices down a little less. However, 3 mm is a long way for this to work. If you can split it into two area, not so much. 

 

Alex


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#3 ChrisWhite

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Posted 09 October 2019 - 09:43 PM

https://agenaastro.c...-extension.html
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#4 Alex McConahay

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Posted 09 October 2019 - 10:48 PM

Which ring is an even better idea than Ace hardware.

 

Alex



#5 ChrisWhite

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Posted 10 October 2019 - 05:38 AM

I will add, that with thin spacer rings don't go gorilla tight.  There is not a lot of material on there and the threads can shear off.  So just snug tight is enough.

 

Also, if you want to post some high res examples, it could be helpful for us to see if it looks like spacing, or collimation, or something else to consider.


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