PhD2 "RA and Dec vary by an unexpected amount...

[Notty]

Hello, so following on from my attempts to test my setup (200PDS, 9x50 finder guider+QHY5L-iic on a newly belt modded HEQ5, I've been having some problems calibrating so I tried again.  I read that sometimes its problematic calibrating using stars too high up so I was using around Arcturus tonight, and I calibrate and get the same "RA and DEC rates vary by an unexpected amount etc..."  I had previously made sure the pixel and focal length were correct in the settings and used the calculated calibration steps of 1200, and I double checked my PA again (using the EQMOD as I always do, no drift alignment but a good alignment using that should be ok, right?)

I decided to accept the calibration and see how the guiding goes, and I've attached some pictures of the trace.  It goes mad in the beginning, then seems to settle down until one blip where it tells me my max RA correction is too low (but I've already got it set to the max of 2000! But it does then seem to get into a rhythm, although I do not know if an acceptable one!

I know the proof is in the trails or lack of, but I was just wondering if looking at this any experts can tell me if I really have got a problem, how bad and any next steps?  I've been reading the documentation on PhD2 and as many back posts as I have time for but I think lots of people may have bee through the pain already.

Inputs greatly appreciated.  

[Leveye]

It's so all over the place especially the RA in the one that I'd venture that wind and balance have a bit to do with it. Have you ever tried the built in drift alignment tool? Works great using bookmarks. You might want to give it a go and see it It steadies things.

[Notty]

Hi thanks, I know it's not wind as I'm in an obsy, and I did balance it beforehand (I'm still not too sure about this East Heavy malarkey though).

Re the drift alignment I do know of this bookmark method but I understand you do need stars quite close to the celestial equator, and I'm surrounded can by trees and structures all around so haven't bothered yet. In any case I've checked and checked and though never going to be spot on I can't believe my PA is to blame for calibration errors?

Once my traces settle down though in the later graphs how bad are they to the experienced eye? Is a RMS of 1.3 in RA excessive? What should it be?

Lots to learn!

[Astroboffin]

Hi,

First of all I would try slightly longer guide suns, of say 2.5 to 3 seconds to try and even out the seeing conditions, you may be chasing it slightly.

Secondly, the guide camera is not a bit loose is it, and moving round a tiny amount, as that would throw off the calibration altogether.

Regards

AB

[SteveA]

I've not had the specific message before, but I have had some similar crazy guide graphs like these with the plots going off scale...so I know your pain!

I spent some very frustrating evenings last summer trying to resolve this sort of thing, despite making just about every imaginable adjustment in PHD I came to the conclusion I had some kind of mechanical issue.

I suspect you may have considered this, as I see you did the belt mod on the HEQ5. I went down the same route and just finished the mod a few weeks back. Having an EQ6 it was pretty much a rebuild job, so I stripped the mount right down and then cleaned and re-lubricated it. I've only just got the mount back in the obsy in the last week or so. Just in the process of drift aligning...BUT I can see my guiding is looking so much better.....really nice relatively flat graphs with none of the massive peeks and troughs. Have you thought about stripping and tuning the mount? I seem to recall seeing that the HEQ5 was easier to mod and didn't require such a heavy duty strip down as the EQ6, so you may not have done. One of the issues I had with the EQ6 was stiff RA & DEC axis, which affected my ability to balance the mount properly, the rebuild finally cured this, I'm not saying the route cause was a balance issue, but in my case it may have been a contributing factor.

Good luck getting this resolved...

[Thalestris24]

Just to add, my heq5 seemed more sensitive to balance after the belt mod. I've been balancing as perfectly as possible in all 3 axes and without it being 'east heavy'. That seems to give me the best results though I still can't get much better than +/- 4 arcsecs with a finder guider.

Louise

[Notty]

Thank you for the tips everyone. I'm going to have the mount stripped and regreased and checked so I can have that in my mind as sorted. If still no joy with that I'll go back to guiding with my ST80 and see if that's any different, though the extra weight is considerable... maybe I should only be imaging on the HEQ5 with my ED80 and a 200pds is pushing it!

Can anyone comment on the issue of highest stars to be viewable in order to drift align? I'd like to get it done once and for all but assumed I wouldn't be able to due to the limitations of my site.