Poor guiding

[Malcolm Aucoin]

I have an Atlas EQ-G equatorial mount that I purchased maybe 10 years ago.  I was using PHD (original) software for guiding.  Had to switch computers and OS so I had to use PHD2.  Since there is more available info with PHD2, I noticed that my guiding accuracy was not all that good.  I get round stars in maybe only 20% of my images. I am using a 430 mm guidescope and imaging through a 914mm reflector. I decided to dis-assemble my mount and re-grease the gears.  I don't know if it is any better now or worse, but I am not happy with it.  I don't know if some of the gear tensioning is too tight, or too loose.

 
Please review this guiding log file.  You can see that the guiding is not very good.  The last 2 sections, numbers 5 and 6, are about 50 minute logs with no guiding commands sent to the mount.  Number 5 is 2 second exposures and #6 is 1 second exposures.  After seeing these, I could understand why the guiding is so bad.  Any help would be appreciated.

[bw_m...@earthlink.net]

Hi Malcom.  I think you may have goofed up the configuration specifications here.  Based on your message, your guide scope focal length should be 430mm – but the PHD2 profile you’re using says it’s 914mm.  That makes It harder for us to analyze your logs but if this really is goofed up,  the guiding is actually even worse than you think.  I think you should start over and get a clean baseline measurement of your mount’s capabilities by following this procedure:

 

https://www.dropbox.com/s/zrf0au7jaisvt85/How%20to%20create%20a%20baseline%20for%20guiding%20results%20using%20OpenPHD2.pdf?dl=0

 

All of that said, I think we’re going to find a mechanical problem in your RA drive system that’s shown here - indicated by the arrows -  in this unguided section of the log:

 

 

These “rough patches” produce rapid RA tracking errors that are actually quite large and really degrade the overall poor RA performance.  Once we get a clean baseline from you, we can probably say more.  When you are ready to upload the data, please use the built-in Upload Logs feature described here:

 

 

https://openphdguiding.org/getting-help/

 

Regards,

Bruce

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[Malcolm Aucoin]

Oh, sorry you are correct.  I was using the 914mm Newtonian for these test guide logs.

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[Malcolm Aucoin]

Thanks and I'll do that baseline procedure.  Yes, I knew those jagged areas were very swift and large changes in RA--a little too much for the mount to handle.

Malcolm

On Mon, Jan 9, 2023 at 10:50 PM <bw_m...@earthlink.net> wrote:

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[Bruce Waddington]

Hi again Malcolm.  Just to be on the safe side, before you invest the time to do the baseline testing, it would be good to double-check that all the EQMOD settings comply with this guide:

https://github.com/OpenPHDGuiding/phd2/wiki/EQASCOM-Settings

I discovered that you had sent us a log back in August with similar poor results.  One problem that shows up in both logs is that the calibration completes too quickly in both RA and Dec, similar to what would happen if the mount isn't tracking at the sidereal rate or the mount guide speed isn't really what the mount driver is reporting.  EQMOD has some 'advanced' options that affect the guide commands so you should be sure those are disabled.

Good luck,

Bruce

[Malcolm Aucoin]

Thanks for the additional information Bruce.  As far as I can tell, all of my EQMOD settings are set according to the recommended settings.  Please see the attachments.

Why is the calibration completing too quickly?  I am letting PHD2 calculate the calibration steps.  How many steps of calibration do you recommend?  I can change the step size to get a slower calibration.  Please see the attachments regarding these settings. 

[bw_m...@earthlink.net]

Hi Malcolm.  I don’t think you’re doing anything wrong, I think there’s a problem with the mount.  One thing you can do just to be absolutely sure is enable the ‘Show Advanced Options” checkbox in the EQMOD ASCOM setup dialog.  That will expose one more control which is a pulse-guide override option.  That must be set to zero and it almost certainly is, but best to be sure.

 

The problem is that even with all the correct settings, the calibration movements are much faster than they should be.  The computed RA and Dec rates that PHD2 is seeing are over 50% higher than the reported mount guide speeds.  Another question is whether the pixel size is correct for whatever DSI camera model you’re using.  The Meade camera driver doesn’t report the actual pixel size so PHD2 is using fixed values based on the DSI model name.  The 8.3u size in your logs is based on the assumption you’re using a DSI II.  Can you confirm that is correct?  If any of the parameters that affect the calculation of the guider image scale are wrong – focal length, pixel size, camera binning – the performance numbers we’re looking at will be wrong. 

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[Malcolm Aucoin]

Hi Bruce.  When I click the "Show Advanced Options" box, the only thing that is different is a settings icon, a wrench, shows up for the "Mount Options Type".  There is a "Pulse Width Override" but it is disabled. Is this what you are referring to? See screen snip.

I have found at least 2 sources that indicate that the Meade DSI II I am using has a pixel size of 8.3u.  In fact, I even measured one side of the sensor (6.2mm) and divided it by the number of pixels on that side (748 pixels) and got 8.28.microns. I got the pixel count from Nebulosity.

I don't understand how the RA and DEC rates are 50% higher than the guide speeds.  Can I "fudge" some parameters somewhere to make that line up, like change the pixel size? And if so, would I have to go larger or smaller? I am guessing smaller.  And how are you making this determination?

Malcolm

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[bw_m...@earthlink.net]

Ok, then it sounds like all the settings are right.  Since we know our measurement scale is right, the reason the RA and Dec rates are “too high” is probably because there’s a problem in the mount firmware or hardware.  I’ll offer an analogy about “fudging” the parameters for this sort of thing.  Suppose I have an older car with a dial-type speedometer.  Could I draw an overlay for the speedometer dial with more tightly spaced speed numbers and tell everyone the car can go 200mph?  😊  As I said originally, these measurement oddities are just symptoms of problems in the mount, just as the rapid oscillations shown in the GA graph indicate mechanical problems. The problem is not with the guiding, it’s the equipment.  I think your goal should be to demonstrate the problem very clearly and then try to get help from the mount manufacturer.

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[rasalg...@gmail.com]

If the version of the mount is 1.06 you have to put drift compensation in 3.

Regards.