Beginner's Guiding issues

[cadman342001 (Andy)]

Ok, so I'm getting into guiding, got my Polemaster regime down pat (or so I thought), guiding seems to be going well (i.e. it is actually guiding after a few teething errors such as guiding on a hot pixel ) but my total RMS error is around 1.5 to 2 arc seconds and I believe less than 1 a-sec is the goal.

So, I'm looking at my graph, referring to the pdf for PHD2, thinking it's a little saw toothed which is over compensating.
Thought I would run the Guiding Assistant first, see what it suggests.

Coming back with big PA errors (11.3 arc minutes !!! - see attached screenshots) and recommending limiting exposures to 2 seconds to combat drift ! wtf ? The polemaster is accurate to within 30 arc seconds but even if I'm doing it badly I can't believe it's as bad as 11 arc minutes !

If the mount isn't exactly level could it cause this degree of error ?

I'm going to try the Sharpcap PA tool tonight but I really thought I had PA really accurate with the Polemaster.

I looked at the PA drift alignment tool in PHD last night but didn't seem easy to do having never drift aligned before. I think the sharpcap program is a little easier to follow? Abit more visual like the polemaster software?

What are your thoughts ? I was doing up to 4 minute subs last night that seemed fine - round stars, but maybe I need to be more accurate for clear sharp nebulosity?

What about the sample graphs - overcompensating ?

Thanks in advance

Equipment:
HEQ5 Pro with Rowan belt mod
AT65-QED
Canon T2i
380mm guide scope, helical focuser with mono skyris cam

[Imme (Jon)]

You say your stars are nice and round? Your guiding graph is fine then.

I think we all get too wrapped up in trying to get a perfect guiding graph.......think about it, if it was perfect without any errors then why would you need guiding in the first place???

You also need to think about scale. Different guide/imaging scope with different guide/imaging camera pixel scale often means a gig error on a guide graph is actually minimal on the final image.


......edit - and just saw your exposure time...0.5 seconds. Go to the 2-4 second mark and I think you'll see the guiding flatten out. At 0.5 sec you are probably correcting seeing issues, not tracking issues

[cadman342001 (Andy)]

Thanks Jon, I'll increase the exposure time and see how that goes.

I do have round stars at the moment but will need to do longer exposures with filters eg H-alpha.

Andy