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  #41  
Old 16-09-2014, 06:14 AM
Garbz (Chris)
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Originally Posted by AndrewJ View Post
I have no idea why PHD2 uses 2 discrete angles, as there is no way to properly measure the DEC angle due to the PE in the RA drive????
If you don't use 2 discrete values then then how can you account for a mount that isn't perfectly polar aligned? If the angles aren't 90deg apart then it's a good sign your alignment is wrong.

Also I can guess that during calibration the PE of the RA axis would be so insignificantly small compared to the step sizes used for calibration that it probably doesn't matter.
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  #42  
Old 16-09-2014, 06:40 AM
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Gday Chris

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If you don't use 2 discrete values then then how can you account for a mount that isn't perfectly polar aligned? If the angles aren't 90deg apart then it's a good sign your alignment is wrong.
For the given step sizes, any polar misalignment error will be negligible,
and the scope was relatively well polar aligned
The angles in question are used to convert the sensor axes to the true RA/DEC axes. The calibration process tells the scope to move in an EW direction and notes the angle and direction that makes on the chip.
It then moves in a N/S direction and again notes the angle and direction.
The EW error angle/direction should become the absolute datum and then the NS angle will be 90deg to that and in the "direction" measured by the cal,
ie RA and DEC cannot be anything other than 90deg apart,
certainly not over 20deg, which is what we saw.

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Also I can guess that during calibration the PE of the RA axis would be so insignificantly small compared to the step sizes used for calibration that it probably doesn't matter.
Maybe, maybe not.
The mount we were testing had an RA drift of 10-15arcsec/min plus a large PE that sometimes matched this. ie In some spots we were seeing local RA error rates of up to 30arcsec/min
Its the only reason i can see that the cal results were so far away from 90deg apart.
Anyway, irrespective of this, i now know that PHD2 converts "for display" based on its cal angles, as I wrote an app to convert the raw X,Y to RA/DEC based on RA being the master angle ( with DEC normal to RA ) and the plots start to make more sense.
I am just suggesting that this is something that you should look at if the data looks suss. I also recon PHD2 should throw a warning if an oddball cal gets registered, as usually, noone looks at that data.

Andrew
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  #43  
Old 18-09-2014, 06:33 AM
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I had another shot last night. I noticed that my filter wheel was a bit loose when connecting to the OAG, and no matter how I tried to tighten it, it would tighten and then come loose again. After switching a few things around there I got that locked up tight, so I removed one potential area for problems.

I didn't bother correcting polar alignment as it was within a couple of arcminutes which I expected to be good enough for these purposes.

I reset all PHD2 settings back to default (as best I can remember) and used Auto-PEC on EQMOD. Actually, I lie, I did set it all back to default but then reduced RA aggressiveness to 80 as it was going nuts. It was still going nuts either way.

Anyway, PEC did more harm than good. I ran it through the full five cycles and had it auto apply. The result was that DEC went off the charts bad, as in it was reading over 5, when I've never seen it go much above 0.7. I quickly disabled this.

This time, for whatever reason, both DEC and RA were jumping all over the place. This was true even after I finished the PE recording and tried to configure it how it was before when only RA was acting up. Disabling guiding on DEC helped, which suggests it was partially software related, but didn't eradicate it.

I think my real problem is that the stars are bouncing around even when guiding is off. I think PHD2 is rightly just trying to correct for problems, but since the star is bouncing around from frame to frame, it's a happy accident when it actually gets it right.

I also screwed around with RA balance, making it varying amounts of east heavy to very west heavy and watched for changes. No apparent pattern to the changes were observed.

At this point I'm reasonably confident that my problems lie with the movement of the star that's present even when not guiding. The question is, what could cause this? I can definitely see some "seeing" issues as well as the stars will get more or less defined. Maybe the bouncing is just seeing as well, but if that's the case I'm permanently screwed because in the weeks I've been trying this the movement has been consistently bad.

Based on previous results I think that the bouncing mainly occurs on one axis, the RA, but I'm no longer sure after last night. If it does mostly occur on RA it definitely suggests to me a mount problem to me. If it was seeing I'd expect it to be more random and showing as much on DEC as on RA.

My plan of attack now is to try and reduce the problem space. The following have already been eliminated from the list of possible primary causes:

1) Balance (adjustment made no observable difference)
2) PHD2 settings (bouncing observed when guiding disabled)
3) Connection between OAG and filter wheel

Tonight I'll try removing the OAG and filter wheel and put the guide cam directly into the OTA and see if it's still bouncing around.

Any ideas on how I could easily confirm / eliminate the RA axis from the list of potential causes? Would pointing near the meridian reduce the impact of RA issues? All of my tests have been done with the scope pointed fairly low on the eastern horizon, as that's where my planned targets have been.

Only once I've figured out what the actual problem is can I then hope to start on the road of fixing it..
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  #44  
Old 18-09-2014, 07:49 AM
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Quote:
Any ideas on how I could easily confirm / eliminate the RA axis from the list of potential causes?
You could try close to 90 deg declination in Octans, and even turn off tracking on the mount. This should show how much PHD wobble there is for stars which really are stationary in the sky.

You would also need to enter calibration data in PHD (if you haven't already calibrated somewhere else), and set it not to send guide corrections to the mount. This way you would just use PHD to plot the unguided movement of a guide star for you.

Last edited by SamD; 18-09-2014 at 07:59 AM. Reason: extra
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  #45  
Old 18-09-2014, 09:06 AM
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Shiraz (Ray)
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Crikey Lee, you are having big problems.

Your original graph showed that the RA is not correcting properly - it gets into a no-mans-land where phd2 is generating lots of correction signals but the mount is not responding. Provided phd is generating normal corrections signals and your mount autoguide speed is set at 0.5x, that still suggests backlash to me (ie the motor is moving, but the gearing is not transferring that motion immediately to the wheel). If you cannot feel any worm slop, it could be due to the internal transfer gears. As others have said and you have tried, you should be able to manage this by offsetting the weights to make it east or west heavy, but the offset weight must be sufficient that it overcomes stiction (ie the mount moves freely under gravity when the clutch is released). If that doesn't help, there is not much left mechanically, apart from bearing preload. If the bearings are too tight, you could get jerky motion - I recently improved my DEC tracking by backing off the bearing preload a bit.

If you are looking low down east, you will be viewing through lots of turbulent atmosphere. The turbulence could have an RA-worse component due to slowly rising plumes of warm air (they don't move sideways, so have less effect on DEC). Maybe do a test up near the zenith and see what happens when you are looking through less air. Imaging below 45 degrees will be a lost cause most of the time anyway due to turbulence, unless your system is heavily undersampled.

Last edited by Shiraz; 18-09-2014 at 11:33 AM.
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  #46  
Old 18-09-2014, 10:48 AM
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PEC should only effect RA, not DEC! Strange. I assume you were guiding when you recorded it - maybe there is an iterative/circular problem here...
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  #47  
Old 18-09-2014, 08:01 PM
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I've been mulling over this problem Lee and something Ray mentioned, has led me to offer another suggestion. The fact that you're seeing weirdness even when PHD is not active suggests that maybe your mount is tracking too quickly (or slowly)...

You've tried changing the maximum duration of the guide pulse in RA to no avail, but what about the minimum? That is, how about adjusting the Guide Speed (0.nn x sidereal rate) downwards, to say 0.25x or even lower the sidereal rate in EQMOD. After all, guiding on the RA axis works by either increasing or slowing the standard guide rate, so as to avoid issues with backlash (DEC works differently, which is why an algorithm to correct for directional shift, such as resist switch, is appropriate).

If this doesn't work, try ramping up the sidereal rate to 0.75 or 1 (or more) -- assuming that you've currently got it on the default of 0.5x. Experiment, and see if this helps...
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  #48  
Old 18-09-2014, 09:14 PM
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Quote:
Originally Posted by SamD View Post
You could try close to 90 deg declination in Octans, and even turn off tracking on the mount. This should show how much PHD wobble there is for stars which really are stationary in the sky.
Thanks mate :-)

Quote:
Originally Posted by Shiraz View Post
Crikey Lee, you are having big problems.

Your original graph showed that the RA is not correcting properly - it gets into a no-mans-land where phd2 is generating lots of correction signals but the mount is not responding. Provided phd is generating normal corrections signals and your mount autoguide speed is set at 0.5x, that still suggests backlash to me (ie the motor is moving, but the gearing is not transferring that motion immediately to the wheel). If you cannot feel any worm slop, it could be due to the internal transfer gears. As others have said and you have tried, you should be able to manage this by offsetting the weights to make it east or west heavy, but the offset weight must be sufficient that it overcomes stiction (ie the mount moves freely under gravity when the clutch is released). If that doesn't help, there is not much left mechanically, apart from bearing preload. If the bearings are too tight, you could get jerky motion - I recently improved my DEC tracking by backing off the bearing preload a bit.

If you are looking low down east, you will be viewing through lots of turbulent atmosphere. The turbulence could have an RA-worse component due to slowly rising plumes of warm air (they don't move sideways, so have less effect on DEC). Maybe do a test up near the zenith and see what happens when you are looking through less air. Imaging below 45 degrees will be a lost cause most of the time anyway due to turbulence, unless your system is heavily undersampled.
That's very interesting actually. I've definitely been below 45 degrees except when drift aligning az. I did try tonight and all kinds of angles and directions, including near zenith and at -90 dec but I still see stars bouncing around.

Quote:
Originally Posted by Amaranthus View Post
PEC should only effect RA, not DEC! Strange. I assume you were guiding when you recorded it - maybe there is an iterative/circular problem here...
Yeah I thought that was one of the more interesting things!

Quote:
Originally Posted by Amaranthus View Post
I've been mulling over this problem Lee and something Ray mentioned, has led me to offer another suggestion. The fact that you're seeing weirdness even when PHD is not active suggests that maybe your mount is tracking too quickly (or slowly)...

You've tried changing the maximum duration of the guide pulse in RA to no avail, but what about the minimum? That is, how about adjusting the Guide Speed (0.nn x sidereal rate) downwards, to say 0.25x or even lower the sidereal rate in EQMOD. After all, guiding on the RA axis works by either increasing or slowing the standard guide rate, so as to avoid issues with backlash (DEC works differently, which is why an algorithm to correct for directional shift, such as resist switch, is appropriate).

If this doesn't work, try ramping up the sidereal rate to 0.75 or 1 (or more) -- assuming that you've currently got it on the default of 0.5x. Experiment, and see if this helps...
Thanks mate, I'll look into that as well :-)

Here's some more charts captured over the past couple of days. I just saw a thread where people in SE QLD were complaining about bad seeing lately, so maybe that actually is a large contributor to my problems. Hope so!

First graph is when I was recording the PE the other night, with mostly default PHD2 settings.
Second is close to the zenith with guiding/tracking enabled.
Third one is close to the zenith with guiding disabled tracking enabled.... note the scale on this one!
Final one is with the QHY5L-II directly in the focuser, not in the OAG... best one, but still not good.
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  #49  
Old 18-09-2014, 09:44 PM
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Lee, I see from your ASCOM settings that your pulseguide rates are 0.1x sidereal! I think this may be the problem... Try changing these values to 0.5x (or more), and see if that helps.
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  #50  
Old 18-09-2014, 09:48 PM
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Lee, if you want to run your logs through PHDLab you will have to edit the mount name in the logs. PHDLab can't cope with the "/" in the name. Change it to any other character - "_" is good. http://countingoldphotons.com/phdlab-downloads/
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  #51  
Old 19-09-2014, 06:09 AM
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Quote:
Originally Posted by Amaranthus View Post
Lee, I see from your ASCOM settings that your pulseguide rates are 0.1x sidereal! I think this may be the problem... Try changing these values to 0.5x (or more), and see if that helps.
good call Barry - that would fit the symptoms
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  #52  
Old 19-09-2014, 06:22 AM
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Yep, increase the guide rate to 0.5x sidereal.

This should improve guiding. Then, lower aggressiveness until you get a flat-ish graph.

And, yep, anything lower than 45 degrees and you're trying to guide through turbulent crap. I have set CCD Commander to only start imaging once an object rises past 45 degrees and to cease imaging/move to next target once an object has set past 45 degrees.

Hope you get it sorted out!

H
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  #53  
Old 19-09-2014, 06:31 AM
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Quote:
Originally Posted by mithrandir View Post
Lee, if you want to run your logs through PHDLab you will have to edit the mount name in the logs. PHDLab can't cope with the "/" in the name. Change it to any other character - "_" is good. http://countingoldphotons.com/phdlab-downloads/
Thanks for the tip! Didn't know I could actually change the name, that was just the default.

Quote:
Originally Posted by Amaranthus View Post
Lee, I see from your ASCOM settings that your pulseguide rates are 0.1x sidereal! I think this may be the problem... Try changing these values to 0.5x (or more), and see if that helps.
Quote:
Originally Posted by Shiraz View Post
good call Barry - that would fit the symptoms
Quote:
Originally Posted by Octane View Post
Yep, increase the guide rate to 0.5x sidereal.

This should improve guiding. Then, lower aggressiveness until you get a flat-ish graph.
I don't recall ever touching that setting until last night; it was already on 0.1 and when I changed it to 0.5 it resulted in an immediate, significant worsening of the symptoms... chart went off the scale so I set it back to 0.1 very quickly.

Quote:
Originally Posted by Octane View Post
And, yep, anything lower than 45 degrees and you're trying to guide through turbulent crap. I have set CCD Commander to only start imaging once an object rises past 45 degrees and to cease imaging/move to next target once an object has set past 45 degrees.

Hope you get it sorted out!

H
Ok thanks, I'll make sure not to do that in future.
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  #54  
Old 19-09-2014, 06:37 AM
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It's all a mystery!

You need to buy a Paramount ME II.

H
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  #55  
Old 19-09-2014, 07:03 AM
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Graph 2 is interesting. You have an FWHM of over 6 on your guide star but your guide exposures are just 1 second. Chasing seeing? Your other graphs have fwhm between 3 and 4. The intent is to make as few adjustments as possible so take longer guide exposures? Also gives all your other settings less to deal with.
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  #56  
Old 19-09-2014, 07:25 AM
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you need to recalibrate phd when you change the guide rate - otherwise it will not compensate by the right amount and you will see wild swings.

Last edited by Shiraz; 19-09-2014 at 07:38 AM.
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  #57  
Old 19-09-2014, 10:04 AM
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Yep, as Ray notes, you MUST recalibrate PHD after making a change in the sidereal rate - otherwise the corrections will be 5 times too large compared to its training movement! I'm still convinced this is the problem.

Task:
-- Set guide rate at 0.5x sidereal in ASCOM (leave other settings as is).
-- Set exposure to 3 sec.
-- Set noise compensation to 2x2 mean.
-- Set RA aggr to 80 and Hyst to 15.
-- Set DEC to resist switch.
-- Set min movement of both to 0.25 pixels.
-- Set max RA and DEC movements to 1000 ms.
-- Point at DEC 0 and maybe 5 degrees east of the meridian.
--(Re)Calibrate PHD. Make sure that calibration used at least 8 steps (if not, adjust the pulse duration in the Brain settings).

Do all this, and report back
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  #58  
Old 19-09-2014, 11:05 AM
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Quote:
Originally Posted by codemonkey View Post
Thanks for the tip! Didn't know I could actually change the name, that was just the default.
Lee, you can't change it in EqMod. You have to edit the log before PHDLab can cope.
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  #59  
Old 19-09-2014, 04:15 PM
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Quote:
Originally Posted by Octane View Post
It's all a mystery!

You need to buy a Paramount ME II.

H
haha. That's it! I'll let the wife know what to get me for christmas ;-)

Quote:
Originally Posted by DJT View Post
Graph 2 is interesting. You have an FWHM of over 6 on your guide star but your guide exposures are just 1 second. Chasing seeing? Your other graphs have fwhm between 3 and 4. The intent is to make as few adjustments as possible so take longer guide exposures? Also gives all your other settings less to deal with.
I suspect this is actually it. I still see stars bouncing all around the place even when guiding is disabled so this suggests to me either:

1) Seeing
2) Mount problems
3) Physical instability somewhere

I saw a thread saying that my area has had terrible seeing lately, so maybe that's all it is. I've done exposures up to 5 seconds long to try and offset seeing, but I was still seeing the star bouncing around from exposure to exposure.

Quote:
Originally Posted by Shiraz View Post
you need to recalibrate phd when you change the guide rate - otherwise it will not compensate by the right amount and you will see wild swings.
Yeah, while that's obvious I'm not actually sure if I did that or not lol. I'll try it again.

Quote:
Originally Posted by Amaranthus View Post
Yep, as Ray notes, you MUST recalibrate PHD after making a change in the sidereal rate - otherwise the corrections will be 5 times too large compared to its training movement! I'm still convinced this is the problem.

Task:
-- Set guide rate at 0.5x sidereal in ASCOM (leave other settings as is).
-- Set exposure to 3 sec.
-- Set noise compensation to 2x2 mean.
-- Set RA aggr to 80 and Hyst to 15.
-- Set DEC to resist switch.
-- Set min movement of both to 0.25 pixels.
-- Set max RA and DEC movements to 1000 ms.
-- Point at DEC 0 and maybe 5 degrees east of the meridian.
--(Re)Calibrate PHD. Make sure that calibration used at least 8 steps (if not, adjust the pulse duration in the Brain settings).

Do all this, and report back
Thanks mate! I'll try that tonight if the weather holds

Quote:
Originally Posted by mithrandir View Post
Lee, you can't change it in EqMod. You have to edit the log before PHDLab can cope.
Ah ok, that explains why I haven't seen a setting for it. Thanks :-)
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  #60  
Old 19-09-2014, 04:48 PM
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Quote:
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I saw a thread saying that my area has had terrible seeing lately, so maybe that's all it is. I've done exposures up to 5 seconds long to try and offset seeing, but I was still seeing the star bouncing around from exposure to exposure.

Not to beat a dead horse here, but did you actually take an image with your main camera yet? The last graph that you said was "best one but still not good" shows +- 1 arc second (assuming that your graph scale is set to arc seconds and not pixels, and assuming you have entered your focal length in phd2)

That would be quite acceptable to me on most nights.
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