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Old 10-03-2012, 10:38 AM
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pmrid (Peter)
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Rotation

I'd be grateful if someone could help me understand what is happening here.

The image is an overlay of the first and last 2 subs in a run of 50x5 minute subs taken last night (I know - moon - but they were taken through Ha). Over a 4 hour period, it is apparent that there has been a rotation the focal point of which is not far below the bottom of the image.
As a matter of possible interest, when I asked my mount to slew to NGC3576, it took me to a position that would probably correspond pretty closely with that focal point of the rotation shown in the image. That may be pure coincidence but because I don't know, I mention it anyway. The mount is a PMX controlled by TheSkyX. I have yet to do a TPoint run so polar alignment is still a little off.
But that doesn't seem to me to explain this behaviour.
Watching these 50 images stack in DSS, I noticed that the offset on each frame went from 0,0 to 105,46 in steady steps - and the image shows it.
SO, any ideas?
Peter
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Old 10-03-2012, 10:45 AM
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Hard to tell for sure Peter. I would rule out polar alignment first though. 20 min and 2 or 3 10 point t-point runs and your polar alignment will be dead on.

The fact rotation is not just in corners though has me puzzled. What scope? Any chance it's deflection of scope or guider?
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Old 10-03-2012, 11:05 AM
Karls48 (Karl)
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Peter, last time I had similar problem was after I rebalanced my scope on HEQ5 mount and left the clutches just finger tight. I donít know anything about PMX mount, so your problem may\ be something else.
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Old 10-03-2012, 11:30 AM
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pmrid (Peter)
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Originally Posted by cventer View Post
Hard to tell for sure Peter. I would rule out polar alignment first though. 20 min and 2 or 3 10 point t-point runs and your polar alignment will be dead on.

The fact rotation is not just in corners though has me puzzled. What scope? Any chance it's deflection of scope or guider?
A couple of things: I just printed the image and using my high-school protractor, located the focal point to within dammit and it is, indeed, pretty well bang on where TSX took the scope on the slew - about a half degree below (on the image but east I think in reality).

The guiding was by OAG so there's no deflection in it. And the scope is well mounted and secure. It's an ED127 but that probably doesn't matter much. The image scale here is 1.94 as/p and the image is a 2048x2048 pixels square. On a rough calculation, the centre of rotation is a shade under one degree below the centre of the image.

It must be something in TSX.
Peter

Last edited by pmrid; 10-03-2012 at 11:41 AM.
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Old 10-03-2012, 11:36 AM
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Make sure you don't accidentally have protrack on. Looks like a constant ra drift. I thought there was a post on mx forum n bisque site about someone having this issue.
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Old 10-03-2012, 11:40 AM
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I presume you were guiding, Peter? Which direction is North in your image?

Cheers,
Rick.
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Old 10-03-2012, 12:05 PM
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I presume you were guiding, Peter? Which direction is North in your image?

Cheers,
Rick.
Rick, hi and welcome back. North is to the left I think. The objects in the image are NGC3576 on top and NGC3603 below it. I think 3603 is to the east of 3576.
I probably have that skew-whiff (not sure about that spelling).

I've added the full DSS stack just to clarify the orientation.

Peter
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Old 11-03-2012, 12:07 AM
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Rick, hi and welcome back. North is to the left I think. The objects in the image are NGC3576 on top and NGC3603 below it. I think 3603 is to the east of 3576.
I probably have that skew-whiff (not sure about that spelling).

I've added the full DSS stack just to clarify the orientation.

Peter
Yep, I agree that it looks like North is to the left. Doesn't really help me come up with any hypotheses though, I'm afraid. Are you still guiding with PhD? If you're using Maxim it might be interesting to look at the log files.

Cheers,
Rick.
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Old 12-03-2012, 05:56 AM
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pmrid (Peter)
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Originally Posted by RickS View Post
Yep, I agree that it looks like North is to the left. Doesn't really help me come up with any hypotheses though, I'm afraid. Are you still guiding with PhD? If you're using Maxim it might be interesting to look at the log files.

Cheers,
Rick.
I've gone back and started the whole polar alignment thing over. If it clears tonight, I'm going to abandon TSX's and Softare Bisque's method and see what good old driift alignment can achieve.
Peter
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Old 12-03-2012, 06:24 AM
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Are you guys referring to this recent thread over on the Software Bisque support forums?

http://www.bisque.com/sc/forums/p/14...029.aspx#58029

First get really good polar alignment via whatever method you like. Please don't be spending a lot of time taking images (and possibly chasing you tail) until after your polar alignment is good. Then do a large Tpoint model (200+ well distributed points) and then turn ProTrack on. It's usually a good idea to take a look at your RAW Tpoint data before doing a supermodel to see what sort of defects Tpoint has discovered. Scroll down and select "Multiple Graphs" as your graph on the lower left hand side of the Tpoint window to see what Tpoint has found.

Last edited by frolinmod; 12-03-2012 at 11:35 AM.
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Old 12-03-2012, 10:29 AM
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Peter

If TSX polar alignment is not working then that points to something else wrong, which may be causing this rotation.

If your location is correct and time is correct and mount is homing properly for Southern Hemisphere then TSX should work. 10 plate solves and it has all it needs to tell you how far things are off. The adjustment it then tells you to do shoudl put things within a couple of arc mins.

Solve that first and I think you will solve your current issue. There is a whole thread in PMX forum about getting polar alignment to work

http://www.bisque.com/sc/forums/t/15049.aspx


Are you using latest Sky X and CCD Soft ?

I see you posted on MX forum. so you should get some answers that way.

Let us know if/when you solve it.
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