For an observatory mounted scope - best software / method for polar align?
I am thinking I should likely improve my polar alignment a tad more - as I reckon an initial configuration I did with my mount years ago probably skewed all results done in the past using Tpoint models and drift alignment.
So I run a Vixen Atlux controlled by a Skysensor2000-PC on a pier in my backyard observatory. The setup doesn't allow a view of the SCP - so the Sharpcap Pro / PHD2 accurate align method of rotating around the SCP and plate solving is likely out.
Also there is a bit of backlash in the Dec gears that needs a slight mechanical adjustment that is on my to do list in 2025 - so I have to note and account for this in the alignment method selected.
But the heart of my issue probably goes back to me doing a three reference star alignment with the SS2000-PC when it was set to polar aligned mode. When it is in this state it runs both the RA and Dec motors to account for drift and King rates of refraction as it track objects - so long as you are within 20 degrees of the SCP!
But herein lies the issue - I tried PEMPro polar drift alignment for hours and The SkyX Tpoint using a 500 star model several times - and the adjustment advice each bit of software gave disagreed with itself over multiple runs with no adjustment to the mount given - I just wanted to see if its adjustment advise was consistent or varied over runs - and it wasn't. It may well have been that the SS2000-PC three star model correction algorithm interfered with either or both the Tpoint and drift alignment models some!
Now after multiple nights guiding with PHD2 for many hours at a time - with the SS2000-PC set in a one star alignment mode (so it is not trying to compensate for polar mis-alignment) it reports a polar misalignment around 16 arc minutes - so about 1/2 a Moon diammeter - so I reckon I can and should do much better.
Guiding is pretty good given the mount is carrying 3 Williams Optics refractors - typically around +/- 0.5 arc seconds (with PEC disabled at present).
So I am left with now SS2000-PC isn't interfering - would I be better of polar aligning once and for all with TSX and Tpoint again (using a large sky model) or PEMPro doing a long duration drift alignment. Too now I believe PHD2 has a drift alignment tool - and that software is generally simple and easy to use.
APT also has a alignment tool and so does N.I.N.A. (which I have never used) and SGP is meant to get one soon.
I recall the Bisque team stating all sky alignment with Tpoint gives by far the best polar alignment to the refracted pole - better than drift alignment. But if I really have been half a Moon diammeter out for years - I would really like to improve this - given its a permanent set up.
I could likely use the SS2000-PC Dec Backlash settings to address the discernible slop in the gears (if not doing so may complicate the Tpoint sky model given the Dec backlash to account for) - or just leave it set to 0 as it is at the moment (as that was the advice PHD gave to ensure best guiding).
What would folk recommend I use for my permanent setup and how should I configure (backlash in Dec compensated for or not, drift alignment method using PHD2 or PEMPro or another large Tpoint model)?
If you can see the SCP then SharpCap is superb at polar alignment. My former set up allowed me to see the SCP and I could align so accurately that the object would stay centred for hours, moving only as a result of refraction and a gentle wobble of PE. It guided superbly!
My current Observatory can't see the SCP and I resorted to using solar noon to get a really good North, and have finessed the dec using PHD.
I'd quite forgotten about PEM Pro, I have a licence and used it a a lot in the past - I must dust it down again! With regards to TPoint, it does improve goto accuracy brought about by telescope and mount defects, but I personally found it more trouble than it was worth. I simply plate-solve and guide these days and it seems to work pretty well.
I'll have to look into Sharpcap for polar alignment and while I'm not familiar with the luxury/convenience of an observatory is drift alignment suitable under such conditions?
I've read so many times DA is the best but not sure on restrictions under a dome, I guess it would be far from easy.
My mount sits about three feet below the rim of my dome - as I reused my old back door when I build my astrolab - and didn't want to be ducking under anything. So I might just be able to view SCP -I will have to test it and see.
The remove Dec backlash idea if one is using Tpoint seems great advice - when I first tuned my mount I address about half the Dec slop - but using the wrong methodology - I actually loosened the motor and connector gear and pushed this assembly toward the worm and locked it in place - because I was inepxerienced and there was no documentation from Vixen on how to actually adjust this! It wasn't until many years later chating to folk at Bintel describing this that Don said - no there should be bolts on the worm drive assembly itself that you turn minimally to move the worm block either towards or away from the motors! So my bad again - will look at stripping teh mount right down and finally tuning that this year too!
The SkyX and Tpoint I use for all basic telescope control and dome alignment. In the past I loved TSX's Closed Loop Slew (CLS) ability to really land me on target. Nowadays I used APT's goto++ telling it to land me within 15 pixels of my target - which it does within 2-3 of its allocated 6 tries refinement moves, then I just let PHD start guiding and I am set until APT does and automated Meridan flip and so on. It is only when I can't find and object in APTs database that I use TSX CLS to get me to the target - then when I know it is correct I simply solve it, define it and add it to APT's custom target database.
Will be keen to see if all modern software agrees with how it wants me to tune the mounts position - given I am starting about a quarter of a degree from true hopefully that should be enough to get it locked wihin say 10 arc seconds of true refracted SCP this time!
The Dome itself per se doesn't make drift alignment more difficult - but the instructions for adding the rails that turn the Dome where a bit wrong so in the next month or so I will replace them all again - with new stainless steel rails and new brackets (from Sirus Observatories). The new brackets extend a few mm further from the dome walls and lower the rails a mm or two closer to the ground - and this should mean the dome is much better positioned for the Motor assembly and means never sticks again! But the height of the mount below the dome ring limits me to targets above 30 degree elevation - which is fine for astro imaging but gives a slight challenge for drift alignment I suppose - aiming lower to the horizon would likely give correct altitude adjustments faster.
Quite looking forward to attempting all these projects this year now that I am retired!
