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Problems with PHD guiding on a CG-5

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#1 Sean13

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Posted 17 December 2012 - 10:48 PM

I just recently got my guidescope in the mail, got everything installed and such on my C6-S with a 50mm guide scope and the Orion SSAG. It connects to the mount and camera fine, does its calibration, and starts to guide. It keeps lock on the guide star just fine, but for some reason it doesn't move the mount quite fast enough to keep up correctly, and over time it gets off. I'm using the default brain settings, is there something I need to change or look at that would be causing this?

#2 Dwight J

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Posted 17 December 2012 - 11:06 PM

Hi Sean: when using a short focal length guide scope like the 50 mm, you need to increase the calibration step size from the default (which I think is 750) to about 2000 to 3000 so it moves the mount enough to show. You can play with the minimum motion which is .15 pixels, firstly by increasing it a small amount at a time, like 0.5 pixels. I find the default aggressiveness setting (100) too much for my mount and you may have to play with this setting as well, fine tuning it for your mount. If it is too high it will always overcorrect and you will be moving back and forth over the guide star. Exposure time is also important - too short and you chase the seeing, too long and it doesn't correct soon enough. I usually use 2 seconds but that doesn't mean that is ideal for your particular mount. Polar alignment and balance is also very important for good guiding. It does take a while fiddling with the settings to get it just right for your mount. BTW, I am picking up a C6 tomorrow and am looking forward to imaging with it as well.

#3 Sean13

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Posted 18 December 2012 - 12:03 AM

Thanks, the calibration steps helped a TON, but I'm still getting a bit of North Dec drift. I have dec drive mode to auto and turn the max dec pulse to 300, and its working better, but still not perfect. Its not overcorrecting, just not correcting enough.

#4 Dwight J

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Posted 18 December 2012 - 12:27 AM

Hi Sean: turn off guiding while looking at the star live. Note which way it drifts in Dec. Then set the Dec correction to either N or S depending on which way you noted it drifted and not Auto.

#5 orlyandico

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Posted 18 December 2012 - 12:40 AM

if it is drifting North, then set the dec guiding mode to North only. And set the Mx Dec to 2000 or so.

if it still can't keep up with the drift, your polar alignment is too far off. since you're using the CG-5, use the ASPA. it can get you pretty much dead center with a reticle eyepiece in your main scope for centering the stars.

#6 Sean13

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Posted 18 December 2012 - 01:43 AM

upped the dec pulse max to 1000 and its tracking like a laser now, thanks for the quick help. I'm freezing my *BLEEP* off out here tonight lol.

#7 orlyandico

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Posted 18 December 2012 - 05:58 AM

arguably.. if mx dec = 300 wasn't enough but mx dec = 1000 can, then that means you could do a better polar alignment :)

a not-so-good polar alignment will show up as field rotation, you'll have to see..

#8 Craig H

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Posted 20 December 2012 - 12:24 AM

+1 for polar alignment... took me two years to figure out that spending an extra 20 minutes each night at the beginning of an imaging session on polar alignment was waaaaaaaayyyyy better than fighting the mount the rest of the night!

Also, I might add that for more consistent results attention to detail helps:
- levelling the mount
- careful balancing

Cheers

Craig.

#9 rmollise

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Posted 20 December 2012 - 08:41 AM

Careful balance is very important.

Leveling the mount? Not so much. It can make the polar alignment process a little easier, but that is all...






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