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  #21  
Old 20-11-2015, 09:43 PM
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lazjen (Chris)
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Cracked the problem(s).

I'm currently letting the PHD2 Guiding Assistant run as I post. It's gone through nearly 2 cycles and my peak to peak is now 11.7. (Conditions here are 20k winds outside obs; skippy sky thinks seeing is going to be a '5'; it's cloud free as far as I can see; I think the seeing is spiking around 3+")

So how did I fix it? Well, the regreasing, etc has certainly helped and I might be able to reduce that number further with some more work in that area.

However the key fix was improving the PA further. You might be thinking wtf, didn't I say it was within 1'? Yes, I did - I unwittingly was telling a Big Lie.

Here's the first lesson: don't believe the PA error reported by the guiding assistant. It's only loosely based on a true story.

When I started tonight, I wanted to capture a baseline before making any other changes, so I thought, go back to basics and check alt/az. I started with alt tonight as I was wanting to do final testing in sky where I would be adjusting the azimuth.

I set up the drift align tool for alt and then get a massive WTF?? From memory it was out by about 13'. As I went to make the adjustment I noticed the locking bolt was not as tight as it could be. I'm not sure why it's that way but I'm getting some suspicions that it's not locking as well as it should and slips over time.

I fix that up and then adjust the azimuth. It was pretty close, but I spent the effort to refine it further. As I was doing it, I noticed that the wilder fluctuations were disappearing.

Finally, I went back to the Guiding Assistant to find the peak to peak value and to see how the graph appeared. It was much shallower of course and didn't have too much rapid changes on the rise. The seeing spikes were more observable (to me at least I think).

I've switched off the assistant and am now guding. The "dart board" is getting better grouping. See the pic below (note the 'y' scale is +/-4"):

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So, stoked to be back in the game again. Thanks everyone for the suggestions.
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  #22  
Old 20-11-2015, 09:45 PM
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lazjen (Chris)
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Quote:
Originally Posted by tlgerdes View Post
Hi Chris,

Your are on the right track with your work block aligning, that and the distance the worm sits out. Common problem of people having the worm block too tight.

One solution to your block alignmernt is the newer one piece design available. But you should be able to get the 2 piece ones working well again. One practice Frogginator taught me was to use the with cover as an alignment square between the 2 blocks, then use a feeler guage set to around 0.5mm and gap the far end block from the mount and tighten.

Trev
Ah yes, this probably helped a bit too. I used a metal ruler I had to assist in aligning them.
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  #23  
Old 20-11-2015, 09:47 PM
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alistairsam
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but if your PA was off wouldn't the drift be in Dec? ra shouldn't show pa misalignment
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  #24  
Old 20-11-2015, 10:10 PM
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lazjen (Chris)
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Originally Posted by alistairsam View Post
but if your PA was off wouldn't the drift be in Dec? ra shouldn't show pa misalignment
Well, I don't know what else to attribute the changes to - I have done 0 hardware (or software) mods since last night, other than PA adjustment.
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  #25  
Old 21-11-2015, 06:30 AM
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billdan (Bill)
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Good on ya Chris,

Glad to hear you are back in the game, now you have to wait for a new moon before you can get serious.
Who would have thought that PA error would change the RA Peak to Peak cycle by so much?
Just shows that in this game you have to cross the T's and dot the I's.

Cheers
Bill
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  #26  
Old 21-11-2015, 08:17 AM
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lazjen (Chris)
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I've got a few other things I'd like to do before the new moon, but I might still take some images anyway. Probably Ha.

When I go out to tonight (hopefully), the first thing I'll be doing is a PA check on alt to ensure nothing has changed there.
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  #27  
Old 21-11-2015, 04:05 PM
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Ryderscope (Rodney)
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That PHD graph is looking much better Chris. I feel a sense of relief on your part as I know how frustrating it can be when things just aren't going well. Conversely it is a great feeling when you kick everything off for a nights imaging and sit back and watch it all happen. Keeping fingers crossed for the next report.
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  #28  
Old 23-11-2015, 07:07 AM
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lazjen (Chris)
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As is usual in this game, the weather has intervened, delaying any further progress.

Time to work on other stuff for a while.
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