Tracking issues?

[edarter]

Hi,

I've always suffered with elongated stars in my images, sometimes worse, sometimes not too bad at all. Its meant that I've very rarely managed more than 60 second exposures with my DSLR, with 75secs on a really good day. I've always put it down to only doing PA by eye despite taking my time to get it as good as I can, and maybe not quite having the Baader MPC not quite spot on spacing wise.

Well today I decided to set up sharpcap pro as I found a topic on another forum describing how to get it working for PA with a DSLR. I was very surprised when it actually worked first time... and worked very well indeed. I can't remember the exact figure but Sharpcap rated it as excellent. I think it was 16secs out?
Anyway, as a test I thought I would take a 60 second exposure of M61, fully expecting it to look ok and be able to push for hopefully 90secs or even 2 minutes. I was majorly disappointed when the image looked no better than when I've PA'd by eye. In fact I would say its possibly worse! Can you cast your collective eye over the image below and tell me what you think the problem may be? Is it tracking, PA, CC spacing..or even a combo of those! I've also noticed that the brighter stars seem to have a 'pizza slice' taken out of them, would that be the focus tube on the 130PDS protruding in to the OTA? I'm feeling quite fed up about all this because its really starting to detract from my enjoyment of the hobby now, I thought a good PA would take me up a step but clearly not

Equipment is 130PDS, NEQ6 Pro, EOS600D, Baader MPC mk3. Unguided but mount and imaging controlled from NINA. And as of tonight PA done in Sharpcap Pro.

Thanks
Ed

[david_taurus83]

Good polar alignment is one thing but it has more of an effect on long exposures. The stars in your image have a streak which looks like a sharp deviation so could be wind, cable swinging about, backlash etc. Neq6 is generally a good mount though so 60s exposure at that focal length should be achievable. Is the mount new?

[MarkAR]

It could also be balance issues affecting tracking.

Edited May 14, 2020 by MarkAR

[edarter]

Mount is probably 6-7 years old. Not used much at all until this year though. Balance wise I thought it was good to be honest. I did specifically check it last night knowing I was going to go for longer subs. 

Could the power supply be a factor? Until last night I had a 13.8v 3.3a supply but during my last session it started to play up so I swapped it out for a 12v 3a laptop type supply. Seemed to be OK but I did wonder if the lack of voltage headroom might cause an issue. Though having said that the star shape issue has always been there so I guess that rules out that theory. 

Thanks

Ed

[miguel87]

Call me old fashioned (I'm 90% a visual observer) but sometimes you have to take a step back and realise that there's very little wrong with those stars (other than colour perhaps).

If you are a perfectionist then I guess it is an issue. But you will get beautiful pictures with the setup just as you have it. I often see stunning images of stacked 30s frames so maybe just stay shorter.

Only my opinion.

[edarter]

Thanks for the encouragement Miguel. Its a single unprocessed frame with an astronomic CLS clip in filter fitted so the star colours would get corrected with proper processing. The shapes though, not so sure. Even when I've stacked images before I've had egg shaped stars. I just expected it to be better to be honest, especially when I see some of the images with similar equipment on the 'imaging with the 130PDS' thread on here.

[miguel87]

You seem well committed so I'm sure you will get it sorted with a systematic approach. I just dont like to see astrophotographers spending hours and getting results that they're disappointed with.

Dont forget to stick an eyepiece in the telescope every now and them. Take a look and chill out. 

There comes a point where you have to be impressed with what YOU have achieved. Comparing to other results is a downward spiral.

It is very difficult to put a personal spin on AP. With normal photography you can take from a  different angle, put something interesting in the foreground, alter composition etc. With telescope AP, the object is just the object, same size, same angle, no foreground, no background.

That is what ultimately put me off; the idea that if I got an exceptionally good photograph and spent hours on exposures, flats, parks, bias, processing. At best, I would end up with something identical to what has already been done.

Anyway, I ramble! But trying to say, enjoy the results from your setup, you are never gonna get the best photo you have ever seen of M42, M57 etc etc, it's just not possible. But, it is YOUR picture.

✌

[edarter]

Ah thank you. Its a fair point and to be honest I have been working on the post processing etc and been quite happy with what I've been doing given so little experience with photoshop. I should use an eyepiece more often though! At least the stars look round at that point lol!

Ed