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Old 18-07-2015, 07:16 PM
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sbig self guiding drama.

wondering if anyone here has had any issues with self guiding going silly and pushing the guide star out of frame during image download? My guiding corrections are sitting nicely at under 0.5px however when the image downloads and the shutter is closed the mount sounds like it is receiving a long guide correction and when the shutter opens the guide star is gone.

This is really ruining my night tonight as I'm forced to sit here and manually abort guiding before images download then restart guiding during the delay before the next exposure.
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Old 18-07-2015, 07:49 PM
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Which software are you using Alex? That might be determinative of any answers we might be able to give you.
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Old 18-07-2015, 07:52 PM
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Sorry how daft of me.

Ccdsoft v5 on windows 7
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Old 18-07-2015, 07:58 PM
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Alas I cannot help Alex.

However, maybe see if you can disable guiding during download. I know Maxim does this with my cameras.
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Old 18-07-2015, 08:23 PM
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Thanks Paul. I used to use maxim 5 years back but cant find the disc or serial anywhere.
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Old 18-07-2015, 09:54 PM
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Which model camera?

The STL11 used to pause when downloading and continuous guiding during download is a recent feature.

Greg.
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Old 19-07-2015, 11:15 AM
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It's an old st2000xcm. The status display indicated that guiding had been paused during image download however when it resumes the star is completely gone from the guiding window and the camera/mount go ballistic trying to recover the star. My first thought was alignment however I was able to run 3 minute unguided exposures with minimal discernible drift so clearly it's the camera/software.

It's done it to me quite a bit but last night it was every 3-4 subs it would go on the Fritz. Sometimes when it resumed guiding the star would be right on the edge of the guide window and it would take 20s to correct it's position. To than end I added a 45s delay between exposures but once it lost the star completely it just went crazy hunting for it.

I am thinking about installing the dithering add-on to ccdsoft to see if that will change things. Failing that I might install the maximDL demo and see if that helps. Failing even that then I will start looking at an external guiding setup.
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Old 19-07-2015, 01:07 PM
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I was going to state perhaps your dithering is too high but if its not enabled anyway, its unlikely to be the cause. The earlier model SBIG self guide cams have no choice but to stop guiding on image download given the camera shutter is closes during ccd read out therefore guide star is lost. Important for full frame sensors but not for interline sensors which can use an electronic shutter.

Without taking images with the main sensor, can you start, stop and start autoguiding successfully and notice minimal drift in the guide star position between each start step? Try short steps first and work your way up to the image download time (say 15 or 20 seconds).
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Old 19-07-2015, 01:37 PM
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I can do 3 minute unguided images with minimal (1-2px) drift and guide indefinitely without imaging with sub pixel corrections. But when it downloads images it makes a massive correction and looses the star (one such correction was 12px in RA. I am wondering if possibly the shutter is sticking a little bit such that the first guide image after image download is blank, the camera initiates a correction then the shutter opens and the next guide image the star is lost.

I experimented with high priority downloads on and off to no avail.
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Old 19-07-2015, 02:26 PM
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Alex, this may seem a silly question but even though the guide star is lost, does you main camera still take images? I am thinking about a mechanical shutter that is sticking - and that would therefore result in a blank guide image AND a blank main camera image.
Peter
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Old 19-07-2015, 03:14 PM
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I don't think it's stuck as much as just opening slowly or with a bit of a delay. I will test it later today
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Old 19-07-2015, 04:19 PM
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Use a larger subframe box around the guide star perhaps? So if there is drift (remember the subframe guide box is highly magnified).

The first thing I would suspect is the star is simply drifting out of the guide exposure frame so try a larger frame.

If that is not it then perhaps reload the drivers as it may be corrupted.

I presume you have been using this camera for a long time and this is new behaviour?

Greg.
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Old 19-07-2015, 04:24 PM
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I only bought the camera a few months ago but it's only done this the last two times I've done it. I will look into a larger subframe size for guiding. Thanks Greg.
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Old 19-07-2015, 04:26 PM
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What is the download time of the image?
How much does the star drift during similar duration if you do not guide?
Are you dithering?
Would be my initial few questions.
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Old 19-07-2015, 05:35 PM
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Download time is about 6 seconds, in 120s I get 4 to 8 pixels drift without guiding and I am not using dithering. I have a 45sec delay between image download and the beginning of the next image exposure, guiding resumes instantly after image download.
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Old 19-07-2015, 06:20 PM
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What mount and scope are you using? Focal length?

What autoguide settings have you set? (exposure length, min/max move)

Even with a reasonable polar alignment a long focal length scope guide star can drift. If your mount has high periodic error then this could drift a lot or if the polar alignment is badly off or the mount poorly balanced it can drift a lot.

Do you get round stars in 10 minute exposures at 1x1 binning?

Greg.
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Old 19-07-2015, 06:23 PM
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Slew to a bright star. Set your guide exposures to say 5 seconds. Set your main camera to the same exposure. Bin x 2 if you need to. Then take images with both as near as possible simultaneously. You'll soon see whether your shutter is sticking because you will get totally blank images (if fully stuck) or images with strong gradients if it is just slow.

Peter
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Old 19-07-2015, 06:57 PM
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Greg:
Heq5 pro that I've disassembled, cleaned lubed and adjusted the worms, also belt driven removing all backlash and the spur gear related error these mounts suffer.
Scope is a 5" f/5 Newtonian. 650mm focal length.

I can run 20 minute guided subs bin 1x1 with no problems

The polar alignment is good enough for 1 minute unguided sub.

Settings as follows.
Guide exposures: 3~5 seconds.
Calibration time in RA and Dec set to 7 and 10 respectively.
Backlash in RA and Dec set to 0 and 0.25 respectively.
Min move 0.01
Maximum move 1.00
Aggressiveness at 6
Delay between corrections is 0
Simultaneous x and y relay activation is on.

Guiding through camera relays and st4 cable to the mount.

Peter. Will give that a go this week. Cheers.


I will post a pic of my calibration results.
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Old 19-07-2015, 08:14 PM
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Thanks Glen.

There is a minimum maximum calculator that can be googled.

I think for Aussie seeing conditions min .5 and max 2.0 are what is likely to be the result. I got better guiding using those numbers. But that would not be causing the problem.

It must be something else.

Greg.
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Old 19-07-2015, 08:50 PM
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Is it possible to disable correction but still have the guide star window open in ccd Soft? This might allow you to narrow down the issue.

Can you try a trial copy of a software which supports dual chip. eg. Maxim?
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