Polar Alignment is Taking Ages...

[AndrewG]

Over the past few weeks I have been getting to grips with a whole new set-up which has been quite good fun.. EQMOD... SGP.... Platesolving  (maybe not so much fun for that bit), although clear nights have been few I have managed to get a couple of images:-

Both images where 15 min subs at -20°C but even after Polar aligning I have some field rotation in the top right and bottom left corners... I have now spent at least 5 hours trying to get it better (3 hours last night but haven't had time to check for improvement).   I have been using PHD2 with the tracking in DX off and have been letting it run for 15 minutes between each adjustment.. After doing Azimuth I then do Altitude but then find if I go back to Azimuth that is out  .. Obviously I understand that it is iterative but based on 15minutes drifting I could be here for years doing it?

Any advice would be welcomed as we do not get that many clear nights up north and spending Winter drifting ain't all that appealing  !

Cheers

Andy

[PNJ]

i have no probs by just using a well calibrated polar scope with eqmod.

I not used software assistant polar align, except eqmod.

but maybe you should try the trusted Drift Alignment using a recticle eyepiece

Paul J

[Owmuchonomy]

I'm learning too. Are you sure it's FR? It could be an issue with chip spacing especially if it's slightly slanted. Interesting comment on PHD2. I just started using 2.3.1c and the drift align appears very easy on the face of it. When I use it the DEC trend line takes about 3 or 4 minutes to settle. I then flick to Altitude and do the same. It's usually close enough for me then, about 0.15 arc mins error.

[Barry-Wilson]

Hi Andrew

Glad to see some images using your Avalon.

For my PA, I use eqmod as Paul does and then I use the drift aligning tool with PHD2.  You shouldn't need to wait 15 mins between adjustments of either azimuth or altitude.  Typically I wait 20 or 30 secs before seeing a drift from the x axis, minute adjustments are needed of course as you zero down on PA.  What error does PHD2 report (it gives a read out)?  You do need a number of iterations as you suggest.

You're probably aware that there other factors in your imaging train that could give rotation - balance, flexure etc.  Have you eliminated these potential problems?

Barry

[ollypenrice]

Keep it simple. Just drfit align using the camera and a virtual crosshair and keep the rest of the software out of it. The software may be OK but you may be using it wrongly, or whatever. Classical drift aligning is software free, or almost.

Olly

[AndrewG]

i have no probs by just using a well calibrated polar scope with eqmod.

I not used software assistant polar align, except eqmod.

but maybe you should try the trusted Drift Alignment using a recticle eyepiece

Paul J

I'm learning too. Are you sure it's FR? It could be an issue with chip spacing especially if it's slightly slanted. Interesting comment on PHD2. I just started using 2.3.1c and the drift align appears very easy on the face of it. When I use it the DEC trend line takes about 3 or 4 minutes to settle. I then flick to Altitude and do the same. It's usually close enough for me then, about 0.15 arc mins error.

Thanks for the comments...

With regards to chip spacing it is something I had not envisaged albeit as I have been tweaking the Polar alignment the amount of rotation has reduced.  The above images at 15 minutes had the same amount of rotation that my original 10 min subs had and a 10 minute sub taken when I did the 15 minute subs just had a slightly oval star.

So I definitely think it is field rotation.. thanks for all the advice.

Andy

[AndrewG]

Hi Andrew

Glad to see some images using your Avalon.

For my PA, I use eqmod as Paul does and then I use the drift aligning tool with PHD2.  You shouldn't need to wait 15 mins between adjustments of either azimuth or altitude.  Typically I wait 20 or 30 secs before seeing a drift from the x axis, minute adjustments are needed of course as you zero down on PA.  What error does PHD2 report (it gives a read out)?  You do need a number of iterations as you suggest.

You're probably aware that there other factors in your imaging train that could give rotation - balance, flexure etc.  Have you eliminated these potential problems?

Barry

Keep it simple. Just drfit align using the camera and a virtual crosshair and keep the rest of the software out of it. The software may be OK but you may be using it wrongly, or whatever. Classical drift aligning is software free, or almost.

Olly

Thanks Barry and Olly for advice and help and yes it is great to get imaging; I must say that imaging with the CCD and Avalon is way better (and easier) than piggy backed SLR, I would say my experience is that DSLR is like old Analogue telly trying to get a decent signal and what I am doing now is uber HD!

That being said if I can get this Field Rotation sorted I will be very happy with the setup.

Barry as you only have to wait 15 seconds or so for it to settle down,  I wonder if my problem is due to the short focal length and that I have been using the Autoguider via OAG to do the drift rather than the Atik One? 

Maybe as you say Olly it maybe better to just use the main camera and use cross hairs to watch the star drift up or down?

Any help as always is most welcomed.

Best Regards

Andy