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Old 18-09-2014, 06:33 AM
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codemonkey (Lee)
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Join Date: Jul 2013
Location: Kilcoy, QLD
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I had another shot last night. I noticed that my filter wheel was a bit loose when connecting to the OAG, and no matter how I tried to tighten it, it would tighten and then come loose again. After switching a few things around there I got that locked up tight, so I removed one potential area for problems.

I didn't bother correcting polar alignment as it was within a couple of arcminutes which I expected to be good enough for these purposes.

I reset all PHD2 settings back to default (as best I can remember) and used Auto-PEC on EQMOD. Actually, I lie, I did set it all back to default but then reduced RA aggressiveness to 80 as it was going nuts. It was still going nuts either way.

Anyway, PEC did more harm than good. I ran it through the full five cycles and had it auto apply. The result was that DEC went off the charts bad, as in it was reading over 5, when I've never seen it go much above 0.7. I quickly disabled this.

This time, for whatever reason, both DEC and RA were jumping all over the place. This was true even after I finished the PE recording and tried to configure it how it was before when only RA was acting up. Disabling guiding on DEC helped, which suggests it was partially software related, but didn't eradicate it.

I think my real problem is that the stars are bouncing around even when guiding is off. I think PHD2 is rightly just trying to correct for problems, but since the star is bouncing around from frame to frame, it's a happy accident when it actually gets it right.

I also screwed around with RA balance, making it varying amounts of east heavy to very west heavy and watched for changes. No apparent pattern to the changes were observed.

At this point I'm reasonably confident that my problems lie with the movement of the star that's present even when not guiding. The question is, what could cause this? I can definitely see some "seeing" issues as well as the stars will get more or less defined. Maybe the bouncing is just seeing as well, but if that's the case I'm permanently screwed because in the weeks I've been trying this the movement has been consistently bad.

Based on previous results I think that the bouncing mainly occurs on one axis, the RA, but I'm no longer sure after last night. If it does mostly occur on RA it definitely suggests to me a mount problem to me. If it was seeing I'd expect it to be more random and showing as much on DEC as on RA.

My plan of attack now is to try and reduce the problem space. The following have already been eliminated from the list of possible primary causes:

1) Balance (adjustment made no observable difference)
2) PHD2 settings (bouncing observed when guiding disabled)
3) Connection between OAG and filter wheel

Tonight I'll try removing the OAG and filter wheel and put the guide cam directly into the OTA and see if it's still bouncing around.

Any ideas on how I could easily confirm / eliminate the RA axis from the list of potential causes? Would pointing near the meridian reduce the impact of RA issues? All of my tests have been done with the scope pointed fairly low on the eastern horizon, as that's where my planned targets have been.

Only once I've figured out what the actual problem is can I then hope to start on the road of fixing it..
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