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I really like my C8Edge but...focusing

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6 replies to this topic

#1 pinzmann

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Posted 14 February 2020 - 07:31 PM

But not thrilled about the focuser. It works fine but coming from a refractor guy, I never really know the location it's in like you do with a Crayford type. Especially now that I'm considering getting a motorized controller. So I have seen a lot of references to the Moonlite focuser.

   So my questions are how much range do you get with a ML? If you set the factory focuser in one position and lock the mirror, can you focus with using the native FL and a reducer? I've looked the the ML and it seems like the travel range is pretty minimal. Once the mirror is locked can I focus with the reducer at f7, pull the reducer off and image at f10 without having to adjust the Celestron focuser?

 Also I may be getting another ZWO AEF as the one I have works well and I can use it with the AIR. Also I don't want to be tied down with needing a computer to manually focus if just observing.

   



#2 Tulloch

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Posted 14 February 2020 - 08:23 PM

Have you considered this?

https://www.celestro...cts/focus-motor

 

Andrew



#3 pinzmann

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Posted 14 February 2020 - 09:13 PM

Have you considered this?

https://www.celestro...cts/focus-motor

 

Andrew

Yes, I did. Only problem is I'm totally dependent on a computer to focus. Unless they've come up with a hand controller for it. 



#4 Tulloch

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Posted 15 February 2020 - 05:19 AM

It does run off the hand controller for the Celestron mount.

There’s a focus menu on the hand box

Edited by Tulloch, 15 February 2020 - 05:19 AM.


#5 pinzmann

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Posted 16 February 2020 - 10:31 PM

Not using a Celestron mount. Using CEM60.

    Is the Moonlite the only crayford style option I have for a C8Edge with the reducer?


Edited by pinzmann, 16 February 2020 - 10:44 PM.


#6 jimandlaura26

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Posted 18 February 2020 - 10:36 PM

Not using a Celestron mount. Using CEM60.

    Is the Moonlite the only crayford style option I have for a C8Edge with the reducer?

Nope. Here’s a good resource to get you informed:

 

https://agenaastro.c...#microfocusers 



#7 carolinaskies

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Posted 19 February 2020 - 09:00 AM

I believe the .7x reducer is parfocal at the F/10 native at it's optimal point, but likely you'll still need to fine focus swapping configurations. 

Typically external SCT focusers have a travel range of 9/10 of an inch which is more than adequate to achieve final focus after rough focus with the primary focuser for the typical SCT. 

This 9/10 design limitations are due to the SCT construction and how it achieves focus by moving the primary mirror which happens to vary the focal length.   The mirror set in an SCT is considered to have it's most beneficial optical quality at the point where the system is at it's rated focal ratio (F/10 for most expect the ACF F/8 and the F/11 Celestrons). 

When you push the focus point out of the tube, optical quality of the image will suffer .  Some external focusers allow the use of a reducer in the system, not sure whether there is a truly viable focuser that isn't a significant expenditure to use the Celestron reducer.  

The Edge has a limited external backfocus of 146mm which becomes a limitation for what you can use behind it. Visually you can get away with an external crayford, for imaging it will become a tight fit and limit the options.  

 




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