Posted 20 January 2013 - 01:53 PM
Is there a guide to PHD guiding anywhere? I have been guiding with the orion st80/ssag combo for about a year now with little to no issues. Well, now that I got my 550d modded and picked up a clip in cls-ccd, my guiding is in the tank. The last three nights of imaging have been useless for me. My set up consists of an atlas mount with their 8in f4.9 reflector attached. I have it balanced so that it is a little heavy on the counterweight side, as well as the camera side in the declination axis. I have updated the firmware for the ssag, uninstalled then reinstalled PHD, and it still gives me poor results. Two nights ago it was taking over 50 steps to calibrate in the N-S axis and the E-W axis, so I changed the calibration step from the default to 2500ms, and that made the calibration take about 13 steps in the E-W but still about 42 in the N-S axis. When I look at my graph, one or both of the lines go off of the charts (last night the blue one was staying on the charts, but WAY off of the mid line, and the red line climbed and never came back. Any ideas?
Posted 20 January 2013 - 02:25 PM
The three areas of possibility is Balance, flexure in the coupling between the guidescope and the imaging scope, or possibly cable catching and dragging.
First thing to look at is to make sure wires and cables are secured with a loop between the moving part of the mount and the fixed part of the mount to allow both axis to rotate in full range of directions that the scope will cover the sky on both axis and the wires and cables can not catch on any mount knobs or levers.
To eliminate balance as a cause, make a test image with the OTA/mount in perfect balance, do not set the balance heavy in any direction. With the clutches released, the mount should turn freely through the full range of motions. If this fixes the problem, then try setting the balance slightly heavy to the east and repeat an image test...
As to flexure, I can not tell you how to test for this, just that there should be a solid mechanical coupling between the guidescope and the imaging scope including the coupling of the cameras to the scopes for both the guide scope and the imaging scope, that any motion between the two combined camera & scopes will create problems with guiding...
One bit of advice, if you have changed to a longer focal length scope in your setup (which is the way I read your post), the longer focal length scope will be more critical to any parameters that affect guiding.
Not only does a longer focal length increase the apparent image magnification, it also increases guiding and tracking errors proportionately...
Posted 20 January 2013 - 02:31 PM
Posted 20 January 2013 - 03:43 PM
Posted 20 January 2013 - 03:57 PM
How are you doing Polar alignment ?
Have you checked your polar scope to make sure it's in alignment with the RA axis?
Are you using EQMOD?
Posted 20 January 2013 - 05:11 PM
Posted 20 January 2013 - 05:17 PM
thanks for the help. It will give me something to do tonight. I imagine that each time I change a parameter in the settings, I should recalibrate. Is this the case? I have not changed a thing, other than what I have done to my imaging camera. I have always guided with the st80/ssag combo, and this scope/mount combo.
Many of the settings can be changed on the fly. Specifically, the ones that show up on the graph.
I'm assuming the problems showed up in your images as well as the graph... What did your images look like?
Posted 20 January 2013 - 05:30 PM
Posted 20 January 2013 - 05:47 PM
Also, what was the sky condition like? Was the seeing bad? How bright was the guide star? I've had several cases when the guide star would disappeared from guide box and I believe it was due to either seeing condition degrading or high thin clouds may have came by. If that happens, sometimes it can confuse PHD and it may have thought the guide star moved too far so PHD over corrected.
Try again next time and make sure the quality of guide star is good. If the seeing is bad, increase exposure to increase SNR. It's okay to increase to as much as 5 seconds. Also decrease RA Aggressive way down to 50-60% for bad seeing conditions.
Posted 20 January 2013 - 06:55 PM
Posted 20 January 2013 - 07:24 PM
You said you updated the firmware for SSAG. Do you mean driver for your PC? If you update to use the latest driver, do you also have latest PHD at least version 1.12? I think the driver that came in CD disk works with PHD 1.11 or earlier. Updating PHD should not affect your previous PHD settings but double check.
It's okay to use a bright guide star, just don't over expose.
If you are using ST80/SSAG, then use default PHD settings. The only thing I would change is RA Aggressiveness for bad seeing condition. If you see a guide star is twinkling quite a bit, lower this setting between 50% and 60%.
Posted 20 January 2013 - 07:52 PM
Did you setup each night you had problems, or did you leave it setup overnight? I think you are saying you leave it setup.
Typically, when I have out of the blue problems like you are explaining, I find that I either forgot to tighten the guide-scope down, or have a cable dragging or not properly seated, or something simple that usually becomes clear in the breakdown. Maybe break everything down, set it back up, re-polar align, and image away and see how it goes.
Posted 20 January 2013 - 09:34 PM
I was imaging (or trying too) the horsehead nebula - pretty close to the ecliptic. The night was cloudless, but seeing was really bad. My exposure for the guide scope was 3.5 seconds. The star was pretty bright, but not the brightest in the frame - should I use the brightest star? I was afraid that it would take up too many pixels and mess up guiding.
Using a bright star for guiding should not be a problem however you say your using a 3.5 sec exposure? In my experience that is way to slow for a bright star. I normally use an exposure of .5 sec to 1 sec for reasonably bright stars in PHD...
I think you should list all the parameter settings on the brain page, a screen capture shot would be nice of all the parameters then we can get a better idea of what is going on...
Posted 20 January 2013 - 11:42 PM
Posted 20 January 2013 - 11:56 PM
Why does the blue RA line on the graph stop suddenly just shy of the middle vertical line at the end of the second box? Did you stop guiding at this point or has something failed?
Posted 21 January 2013 - 12:14 AM
Thanks for the help!
Posted 21 January 2013 - 12:22 AM
Posted 21 January 2013 - 01:09 AM
Then in the EQMOD/ASCOM I run the sliders under pulse guiding "rate" up to 30 to maybe 40.
before adjusting the rate in EQMOD my calibration was all over the place. I would certainly get the MAX dec and the rate adjusted first thing and see what that does for you.
I dug up this thread I posted back in August of 2011 PHD Settings Well Explained
Posted 05 May 2013 - 11:32 AM
Thanks for the help!