Re: Guiding...How out of focus?

Steve Reilly

Thanks for the reply Roland. I checked and when guiding with the internal guide chip it’s rock steady. I double check the physical connection at the scope and it’s tight with no cable drag. I did investigate a bit more and posted a screen shot of a plate solved NGC7635 which shows the FOVi for that setup. It appears to be one star until you zoom in. I posted a few screen shots of that as well at higher zoom rates as noted in TSX. See for additional screen captures. I checked a few other targets and found that at my normal 2.66 scale for the FOVi gives me the main and guider chip placed to see both. At this scale I didn’t notice the second star on maybe 3 targets I have selected in ACP Expert. One other aspect I’ve noticed is the active area that MaxIm responds to the guide star meaning that in earlier versions your guide star could be closer to the perimeter and still be recognized whereas now not nearly as much so placement is more critical especially when dithering.


My imagine system is a 12.5” f/9 RC so the focal length should be 2857mm and yet it seems to be 2980mm. Not sure if that gives me any room to move things to get better focus or not. I’ll check with John Stiles to get his thoughts. The other thought is that I was thinking of replacing the remote guide head with a standalone guider such as the Starlight Xpress X2 or Ultra mono versions. Both give larger field of views and have a whole different profile making it easier to mount in tight places. I also expect it has a different spacing from OAG mirror to chip than the RGH so there’s that as well. But before making any changes I really need to make sure I’m moving in the right direction.


I also have the AP 67 reducer but not sure if this can be used with my RC or not. Forget that, I still need the flattener which takes a good deal of backfocus. Does rearranging the image train make any sense? Like moving the OAG to between the rotator and the flattener? The MMOAG does have helical focuser that can be used but in this case it’s straight MMOAG to RGH.







From: <> On Behalf Of uncarollo2 <chris1011@...> via Groups.Io
Sent: Wednesday, December 18, 2019 9:13 PM
To:; bblackwell13@...
Subject: Re: [ap-gto] Guiding...How out of focus?


Hi Steve,


Your image is probably not out of focus, nor does it appear to be 2 stars close to each other. It looks like your optics or camera are vibrating, perhaps because of fan vibration on the back of your camera. Try turning off your fan to see if the image stabilizes. We had similar problems with an FLI camera at our remote observatory and had to change out the fans which vibrated enough to cause elongation and/or double stars to appear in all our images.






-----Original Message-----
From: Steve Reilly <
To: main <>; 'bennie blackwell' <bblackwell13@...>
Sent: Wed, Dec 18, 2019 7:26 pm
Subject: [ap-gto] Guiding...How out of focus?

So I’ve been experimenting with my STL-11000M and the Remote Guide head I’ve had for a long while. My imaging train consists of (from the rear cell to the camera) an Optec 3” Rotator, OGS Flattener for my 12.5” RC, MMOAG (AstroDon) with the RGH, 8 position filter wheel, and STL-11000M. Maybe I’m missing something but I seem to have an issue with getting the off axis guider image to focus. I come close but not there. I realize we’re guiding on the centroid and sharp focus, at least as I’ve heard over the years, isn’t critical but how far out can it be? I’ve posted a page showing the telescope with the imaging train as well as two guider image screen captures. The focus is not good but it does seem to guide on some stars better than others. In this case I’m almost certain it must be a second star that appears at times. Of course if the focus was better it would be more clear.


So how far out of focus will guiding likely work? Do I need to try to get the focus better to get reliable focus with this system? Using the internal guide chip works great except it’s behind the filters hence the MMOAG. As the physical setup is now I would need to move the RGH closer to the pick off mirror and it’s as far as it will go. There is nothing between the RGH and the MMOAG like the includes helical focuser which only spaces it further out. I’m clueless as where to start. The flattener itself is one piece and there are no adapters on it so there is no adjustment to that as well as the Pyxis (Rotator). I guess one possibility is a shorter flattener but I’m not aware of any for a RC.


The spacing is correct for the system as seen.  Link to page is


Thanks for any suggestions.



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