message indicating DEC guiding problem

[pauls...@gmail.com]

Hello,

I was taking some images if the leo trio of galaxies last night and PHD2 provided an error message indicating it wasn't able to make effective DEC corrections. The star images in all the subs were elongated. I have pasted the logfile link below:

 https://openphdguiding.org/logs/dl/PHD2_logs_977W.zip

many thanks for any help on understanding and correcting the problem.

if it might help to have any further info, please let me know.

thanks and best wishes

Paul

[Brian Valente]

Hi Paul

Your logs indicate a couple things:

1. the guidestar was lost for quite some time, and therefore no guiding was possible.

2. your dec axis shows a lot of backlash, but you do not have auto backlash compensation enabled. the message probably came from the start of your session where it took quite a while to reverse dec direction.(around 10 seconds). After that it shows your corrections were largely in one direction, so i would revisit your polar alignment as well

3. your last calibration indicated an orthogonality error, but it apparently never got resolved? An ineffective calibration is going to compromise your guiding 

4. your mount exhibits an extremely large periodic error, nearly 30". what kind of mount is this? PHD does a good job guiding this out, but it can only do so much

I suggest you re-run your calibration using the calibration assistant, and follow it with a guiding assistant run including backlash measurement. 

That should help and also give you a better idea of what's going on and how much backlash you are dealing with. If you continue to have problems, posting the log with calibration and GA run will help clarify what's going on.

Brian

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Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[pauls...@gmail.com]

thanks for reply Brian, much appreciated.

re your numbered points:

1 - I use NINA and neglected to auto restart guiding which probably explains the guide star loss. I have rectified that in NINA.

2- I have now enabled auto backlash compensation, thank you for that. I used NINA's three point polar alignment tool and it indicated PA was within 10 arcmin (for each of az & alt) which I hoped would be good enough (as on a different mount - mesu 200, i have PA error of 6 arcmin and PHD2 does a great job with that - uses oag on an sct)

3- does this indicate a manufacturing tolerance or more likely my guidescope is misaligned in some way? Can I do iterations of  measure & adjust to make the orthogonality alignment better?

4 - the mount is a skywatcher star adventurer gti, max payload 5kg (my current payload is a canon 1000d with 200mm lens + guidescope - weight 2.5kg)

I note with the mount that the RA backlash seems minimal when unpowered and moved gently by hand, but when doing the same with the DEC axis, there's a noticeable movement I'd say probably one degree which seems large, but I have no experience of geared mounts, just the zero backlash mesu.

I'll do as you suggest re calibration assistant and guiding assistant and see how that goes.

thanks again,

Paul