Drift alignment with significant periodic error

[SteveBz]

Hi People,

I'm about to re-embark on everything I need to do to get a decent photo starting with polar alignment. I've always relied on getting Polaris in the little circle as being enough, but as my photos are still rubbish I've decided to take everything to the next level, pa, collimation, focus and guiding. Starting with pa.

I know from my attempts at guiding that I have serious PE on my old reconditioned cg5. So my question is , won't drift alignment be frustrated by PE? Should I calculate my PE frequency and then measure the period of drift alignment in these periods, about 10 mins I think.

What do you say?

Thanks

Steve.

[Ibbo!]

The PE will not be an issue as you are concerned with the DEC drift just make sure you camera is orthagonal with the RA & Dec.

[Thalestris24]

Hi

I don't think you should have a problem adjusting PA because of PE (which fluctuates slowly) but you may have problems because of backlash and balance. You need to tune out as much DEC backlash as possible. You need to make sure your setup is properly balanced. I'd recommend using the PHD2 tool for drift aligning. In what way are your images 'rubbish' at the moment? Analysing problem images can give a guide to what might be causing problems.

Louise

[SteveBz]

16 minutes ago, Thalestris24 said:

Hi

I don't think you should have a problem adjusting PA because of PE (which fluctuates slowly) but you may have problems because of backlash and balance. You need to tune out as much DEC backlash as possible. You need to make sure your setup is properly balanced. I'd recommend using the PHD2 tool for drift aligning. In what way are your images 'rubbish' at the moment? Analysing problem images can give a guide to what might be causing problems.

Louise

Hi Louise,

Maybe rubbish is too strong, but I think they could all be much better.

Hereis my sgl album:

https

 

[pete_l]

I took a squint at the M92 image from your collection. It doesn't look to me like you have any PE, guiding or other issues.

[RayD]

If you are concerned about PE, which I think most would agree shouldn't be an issue, have you considered using something like Sharpcap or even a Polemaster, and then just using drift alignment by way of double checking?

[SteveBz]

23 minutes ago, RayD said:

have you considered using something like Sharpcap or even a Polemaster, and then just using drift alignment by way of double checking?

Well polemaster is a bit expensive but the sharpcap idea is given here:

"How does it Work?
The polar alignment works by analyzing two pictures taken of the area near the pole. You take one picture, let SharpCap analyze it, rotate your mount by about 90 degrees about the RA axis and take the second picture. By recognizing the stars in each of the pictures, SharpCap can work out two things:

1. The exact area of sky represented in each image - this process is called Plate Solving. SharpCap has a built in plate solving algorithm that doesn't need an internet connection or any other program or database to be installed. SharpCap's plate solving only works within 5 degrees of the pole though (N or S).
2. The center of rotation about which the stars seem to rotate when going from the first to the second image.

Since SharpCap has worked out exactly what RA&Dec the telescope was pointing at in each image, it knows where in the image (or perhaps how far off the image) the celestial pole is. It also knows the point about which the stars seem to rotate - that's where your RA axis is currently pointing. If those two points are the same then your polar alignment is perfect. If they are not the same, all you need to do is adjust the Altitude and Azimuth adjusters of your mount until they are the same point and you have completed your polar alignment."

And I could certainly replicate that calculation, what a great idea. Thanks very much.

Steve.

[Thalestris24]

Had a quick look at some of your subs - they don't look too bad! Maybe focus is a little off in some and maybe processing could be improved (I can't shout - my own is pretty feeble...).  Just need a few tweaks here and there.

Louise

[SteveBz]

36 minutes ago, pete_l said:

I took a squint at the M92 image from your collection. It doesn't look to me like you have any PE, guiding or other issues.

Hi Pete, it's very kind of you to say so, but generally I feel my stars are too blob-like and not point-like enough. I never manage exposures longer than 120 secs and most are 30-45 secs. I'd like 3-5 minutes. Of the shorter exposures I throw away 40% and of the longer exposures I throw away 80-90%.

Thanks

Regards

Steve.

[newbie alert]

Guiding will change the whole ball park..but as you say starting with PA  and getting everything as good as poss the jigsaw will fall into place...guiding will give its own frustrations but it's all a learning curve..a frustrating enjoyable one