New SGP Trick


I tried something last night which I’d like to share. I have a folder of SGP Sequences call “Calibraition Stars”. I usually start by selecting an appropriate star and get everything focused and synchronized before I start my imaging. Last night I selected Deneb. Here the trick I thought of. I moved Deneb until it was in the center of my off axis guider. I changed the cooordinates to that location and used “Save As” to save a new sequence. Now I have two Deneb sequences. One that centers Deneb in my main camera and one that centers Deneb in my OAG.

Now I can use auto focus the get my camera focused, then use my Bahtinov mask to focus my OAG on Deneb.



Not sure if this would fit with your workflow but you could also use the ‘Focus and Target Positions’ feature to achieve something similar. The target position could be the position with your star in the centre of the main camera, the focus position the star in the centre of the OAG camera.


For whatever reason (and it has never been identified ….) my ‘centre here’ option does not work and has never worked. Despite having accurate data in all the relevant settings, if I do ‘centre here’, the actual centre will always be moved off screen, leaving me totally blind - not knowing whether it was up or down etc. this bug was in v2 and remains in v3.

Lawrence Harris


Mike: Thanks for your response. Sounds like a better way!


L_Harris: Thanks for responding. I have never had any problems with SGP centering.


why do you need to focus the OAG on a regular basis? are you setting up and tearing down every night?

in my case i set my OAG focus 5 years ago and never touched it again…



pfile(rob): You’re absolutely right. I’m getting ready to move everything up to OkieTex and thought I had an interesting solution to focusing my OAG. On a regular basis, I never touch it. Thanks again.


that’s good, because it’s kind of a pain :slight_smile:


My center here has always worked in all versions, two operating systems and two different mounts, which kinda suggests it is not a software bug. I think it is more likely to do with settings or the mechanical limitations of the mount. Things to look for are Epoch settings, conflict with models (like those in TPoint or EQMOD) and good old backlash.


Hello Buzz

In my defence, before trying it each time, I ensure that the scope has
been synched via plate solve and that all settings are otherwise OK. I
then try a ‘centre here’ using an easily identifiable bright star. Every
time, the scope then moves off the field leaving me lost.

I will keep trying …




Lawrence - is the mount applying any kind of pointing model? The behavior you describe has been seen before - but was attributed to things outside of SGP screwing things up.


Not to my knowledge. It is a Celestron 11 Edge run via ascom. Well polar aligned but no further alignment is done; I use the option ‘quick align’ which means that it is not using any further alignment - eg stars. It will then run SGP right off but I usually do the PHD2 guiding calibration and check focus. All working fine. Lawrence


Lawrence - I would do a forum search for similar issues. If my memory serves me right, it was a Celestron that was having issues before. The sync was making things worse, not better. I seem to recall that this was a limitation of the mount itself.


I should have mentioned that the mount itself is the Celestron CGX. My main problem experience so far (apart from the wedge failure that had to be returned for repair) is that goto is good on the west side of the pier but not necessarily so on the eastern side. (Or I might have remembered it the other way round!). Either way, SGP copes very well with the slew corrections when enough ‘tries’ are permitted! Lawrence


I know your frustration. Last week I had three perfect nights where my mount suddenly decided it was in the Southern Hemisphere. Every time I when to a target, it ended up counter balance weight up! Turned out that my computer clock ( which never gets connect to the internet) had an AM time, not a PM time.



Bob - for info, I run Dimension4 NTP on boot up of my PC. This gets me within 50ms or so. It runs a log file of the corrections. I was horrified at the inaccuracy of both of my PC clocks. I think they must use cheap resonators and rely on an Internet connection to correct the time each week.


I have never had to change focus on my autoguider since I initially set it up.

John C


I don’t know whether I subsequently posted on this non-centring problem but after someone offered to help, the scope stopped trying to spoil imaging runs and since then it always centres properly!

Lawrence Harris