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auto focusing for Celestron SCT

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#1 palaback

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Posted 16 September 2019 - 12:34 PM

I have started to use my Celestron 9.25" for astrophotography, both deep sky and planets. Would really like to set up a autofocusing system to improve focus, and to better deal with changes in temperatures too. Moonlight gets rave reviews, but is the most expensive, on the other extreme some people use the pegasus focus cube, primalucelab sesto senso, or similar units. So far I am leaning towards the nstep focuser, motor and controller or the moonlight. The moonlight replaces the focuser, allows the reducer to fit inside, so may create issues for back focus (I would have reducer, OAG, DSLR and maybe someday a filter wheel & CCD) and is quite heavy, but is a much more robust focusing system; the nstep the focus cube and others use the existing focuser, so less robust but avoids issues of back focus and is fairly light weight. Still wondering if the moonlight is worth the extra price and if anybody has run into back focus issues, or if using the existing focuser works well enough for photography, or if there are other issues I should be thinking about.


Edited by palaback, 16 September 2019 - 12:48 PM.


#2 rkinnett

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Posted 16 September 2019 - 01:25 PM

I get good results focusing my C9.25 using an old JMI NGF-S (Crayford style) with Motofocus and a Shoestring FCUSB2, purchased all together on CN for ~$100.  I have no problem finding focus (first with the manual SCT focus control knob, then fine adjustments with the JMI focuser), with an Orion TOAG and asi1600 with filter wheel. 

 

Before I bought the JMI focuser, I looked at a secondhand non-motorized Moonlite in the classifieds but the guy was asking almost retail price for it, and it didn't have the necessary adapter for a C9.25, and those adapters are absurdly expensive.  I was intrigued by how the Moonlite carries the SCT reducer/flattener internally, but my C9.25 had plenty of focus range and didn't need that optimization.  My plan was to build my own driver for the Moonlite if I had found an affordable one, but in the end the NGF-S works just fine at much lower cost and effort.

 

I also briefly used a JMI SCT focuser which made manual focusing easier via the included pushbutton controller.  I experimented with operating that focuser remotely (with the FCUSB2 interface) instead of the NGF-S.  It was easy to focus manually but autofocus in Ekos was unreliable.  It worked sometimes but usually lost the target star when the mirror shifted.  I have read that people have gotten it to work in various other imaging software packages by forcing the autofocus routine to avoid changing direction.  I did not look into that myself because the NGF-S works just fine.


Edited by rkinnett, 16 September 2019 - 01:26 PM.


#3 Don W

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Posted 16 September 2019 - 05:39 PM

Have you looked into the Celestron Motorized Focuser? I've been looking myself and ordered this one last week.

 

https://www.cloudyni...sct-and-edgehd/



#4 freestar8n

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Posted 16 September 2019 - 06:26 PM

I have used a simple stepper motor on the primary knob with autofocus software on c11, edgehd11 and edgehd8 and it works very well for deep sky imaging. You just need to allow about 1/2 turn for backlash compensation and finish focus turning ccw. My images reach below 1.5” fwhm with periodic focus about every 40 minutes.

Frank

#5 LPA

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Posted 19 September 2019 - 09:12 AM

I have an EdgeHD11 and originally installed a MicroTouch for autofocus. It worked well and it allowed me to incorporate @focus3 within the SkyX Pro as an integral part of my imaging sequences. But even with Celeston's 0.7x FF/FR I found that camera rotation is important for many DSO targets. So I purchased a LiteCrawler. Now I can use Stellarium to plan ahead of time what is the best position angle for my camera and then use the rotator to put the camera into that position. An additional benefit is that the LiteCrawler allows me to lock the mirror in place after using the C-11 focus knob to put focus into the middle of the LIteCrawler's focus range. That is something I only needed to do once since I always image with the FF/FR. Back focus is not an issue. I have an FLI CFW2-7 filter wheel and ASI1600mm-pro attached to the LiteCrawler or I can use instead my ASI071 without the FW. Everything runs smoothly. Note that the NiteCrawler uses too much back focus for the EdgeHD's which is why the LIteCrawler is needed.


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#6 Old Man

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Posted 25 September 2019 - 02:24 AM

Due to some serious health issues and old age, I developed pressure tremors in my hands. So anytime I tried to focus manually it just led to an issue of frustration and anger. I went with the Rigel nstep system, it was the difference between giving up the hobby and once again enjoying it. Leon went the extra step and custom made mine as no one made a motorized version for my scope, like me it is outdated.

  My vote is for Rigel Systems, I cannot say enough good about them, and I love mine.

 

           Mike


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#7 Tapio

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Posted 25 September 2019 - 03:58 AM

I just installed Pegasus FocusCube 2 for my 8" SCT.



#8 LauraMS

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Posted 26 September 2019 - 12:07 AM

I have a Moonlite 2.5inch motorized focuser for my Edge 11 and I like it verymuch  - operates smoothly without any issues, mechanically very stable, I can lock down mirror locks. Just perfect IMHO. And it looks very nice smile.gif. Recently also bought an 2. 5inch Moonlite for my Skywatcher Newtonian because my experience with the SCT version was that good - got it used for a good price and added a new motor.

 

Before that I had a motorized Baader Steel track (first version) mounted initially on my Nexstar 8SE and later on my Edge11.  Wasn't really happy with it on both systems and swapped it for the Moonlite.

 

@LPA: I haven't heard of the Lite Crawler - is that an older product not produced any more? The backfocus issue was the reason I didn't buy the NiteCrawler for my Edge11, so any info would be appreciated.

Laura


Edited by LauraMS, 26 September 2019 - 12:17 AM.



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