PHD2 Problems Controlling CGEM with ASCOM

[BigDan]

Maybe I need to update my Celestron ASCOM driver, but it was updated recently.  I have a CGEM less than 1 yr. old from new, am running ASCOM from USB on my laptop to the serial port on the HC.  I am running the newest version of PHD2...... I think it's version 2.6.2.  I noticed recently my guiding went haywire.  I am able to control the mount when loading the ASCOM driver directly and giving mount commands from the ASCOM software, I can operate the mount using either Celestron's Nexremote program or Stellarium, using the ASCOM platform. 

When I launch PHD2, specifying the Celestron ASCOM driver for mount in PHD2, my guiding is literally off the chart.  I can click connect, and PHD2 tells me I am connected for both mount and camera.  After connection, I begin looping (taking short exposures).  I then go into a drop-down menu above, and click on Manual Guiding.  I can not move any of the stars when I do that.  In fact the Manual Guiding screen freezes up..... I can not close the window.  But eventually it closes..... may take a full minute.  When I originally connect to the mount in PHD2, the ASCOM control icon appears on screen (N/S/E/W), and I can move the scope with that.

So..... I tried going back to specifying "On Camera" for connection to mount, and using the ST-4 cable for connection directly between guide port on camera, and guide port on side of CGEM.  When I do this, my guiding winds up being fairly acceptable.....  obviously guiding is occurring.  However, when using the ST-4/ "On Camera" hookup, I still cannot see any movement when I try to move the stars on screen using the Manual Guiding tool.

For now, I intend to stick with the ST-4 cable, and at some point update the Celestron ASCOM driver, to see if I can go back to ASCOM.  But it doesn't really make sense that I can control the mount via ASCOM with Nexremote and Stellarium, but not PHD2.

Any ideas will be appreciated.   

[bw_msgboard]

Hi Dan, see below.

 

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Sure, it makes sense.  PHD2 is using the ASCOM pulse guide commands – all the other apps are using slewing commands.  They’re completely different things other than using the same USB cable and driver.  You should probably look into why the ASCOM driver might not be handling pulse guide commands, perhaps it’s just an option in the setup.  If you want to stay with ST-4 guiding, that’s ok but you should at least keep the ASCOM link as the ‘Aux connection’ in PHD2.  That way, PHD2 will have pointing and guide speed information from the mount, things that are useful for many reasons.

 

If you decide you want to figure out what’s wrong, you’ll need to submit both the guiding and debug log files from your failed session with ASCOM pulse guiding.  Your problem description doesn’t contain enough detail to know what’s happening – but I would check first about pulse-guiding support in the driver.

 

Good luck,

Bruce

 

Any ideas will be appreciated.   

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[Vince]

Dan, for what it's worth I am using PHD2 v, 2.6.2 with a CGEM via the Celestron ASCOM Driver and have no problems.  I would make sure you are using the most recent Celestron driver published in May on the ASCOM site, http://ascom-standards.org/Downloads/ScopeDrivers.htm.  Also, I do not see in the driver interface any option for pulse guiding.

Vince

[BigDan]

Thanks very much for that, gentlemen.  I will use the ASCOM driver as the auxiliary connection, and try updating the Celestron ASCOM driver.  Thanks.

[peter wolsley]

Sorry you are having issues with your CGEM.  I own a CGEM and have no problems using ASCOM pulse guiding with PHD. Posting your guiding log and debug log is going to tell us a lot..  I assume that you cannot calibrate PHD when using the ASCOM pulse guiding method?  I would check that the autoguide gain is set for 50% for RA and for DEC in the mount.  You can find out what PHD thinks the autoguide gain is by using the PHD "brain".  Call up the "Guiding" tab and then click on the "Calculate..." button.  The value shown for Guide speed n.nn x sidereal is the autoguiding gain value that PHD got from the Celestron ASCOM driver.  A good value for this is 0.50 which is equivalent of 50% autoguiding gain.  I am hoping that PHD displays a very small value.  This could explain why long guide pulses via ASCOM don't do anything.

Could you also explain how you have your Celestron software configured when using ASCOM.  For example...I use Nexremote with ASCOM full time. I align/calibrate using Nexremote and I have ASCOM using the virtual com port provided by Nexremote.  Nexremote connects to my CGEM mount using a USB to serial module using COM4.  I don't press any buttons on my physical handcontroller to align/calibrate/slew or goto.

Peter

[BigDan]

I downloaded the newest ASCOM driver for Celestron last night.  That did not help.  I can do guiding if I do the On-Camera/ST-4 hookup, and I think I can specify Celestron-ASCOM as the auxiliary driver.  I am a weekender at my dark site.  Weather permitting, this coming weekend, I will do some guiding and provide guiding and debug logs.  My cable hookup for ASCOM is serial cable from the HC, to USB adapter, to USB port on laptop.  I get "Connected" to mount shown by PHD2 when I connect to mount using the Celestron-ASCOM driver.

I am wondering if in the Manual Guiding window, if I click one of the buttons, say.... North..... several times, if it takes quite a few seconds to show up on screen, and if it should be easy to detect star movement on screen when I do that.

I will look in the ASCOM profile as to whether there is an ON/OFF option in there for pulse guiding.... probably not, but I'll look.

[CyScape]

I am wondering if in the Manual Guiding window, if I click one of the buttons, say.... North..... several times, if it takes quite a few seconds to show up on screen, and if it should be easy to detect star movement on screen when I do that.

How long it takes to move depends on your exposure, and if you blink...you could miss it, then wonder,"did it move"? Use the "fine grid" overlay to track movements.

[Andy Galasso]

Dan, You can increase the size of the guide pulse to send a larger duration guide pulse to the mount which should result in a proportionally large star motion:

You could use a bookmark (menu: Bookmarks) to mark the starting position of the star.   For example: select a star by clicking on one, then menu Bookmarks => Bookmark star pos.

Andy

[BigDan]

Thanks for all these suggestions.  I will implement and get back.  This weekend is probably bad since I'm in Florida and so is a hurricane.  I'm still leary about my ASCOM setup, though..... PHD2 tells me I'm connected with the Celestron/ASCOM driver, but guiding is literally off the chart.  Switch to On-Camera/ST-4 hookup, and everything stays on the chart at 2 arc deg.  Will get back to you guys after I implement these ideas.  Thanks.

[CyScape]

Stay safe Dan!

[BigDan]

OK.... so last night, I played with PHD2 for a while, specifically to see if I could get movement, all 4 directions, using manual guiding.  I was connected using the Celestron/ASCOM driver.  At first, I could not see any star movement on the screen.  So I put the fine grid on the screen, and I had the movement per pulse set to maximum (5,000).  I still did not see any movement.  Then I thought that maybe there was an option in the hand controller to allow the mount to do guiding.  What I found was Autoguide Rate.  It was set at 50 for both RA and DEC.  I set them both to 99.  I then went back to the Manual Guiding screen, and at first did not see any movement, but doing 3 clicks each direction, there was movement consistently.  I did some guiding on a star, ran Guiding Assistant initially.  It was a pretty good looking graph..... pretty tight.  I think adjusting the Autoguide Rate was a major improvement.  I'm going to try doing some imaging this evening, and I'll get guiding and debug logs to this thread soon. 

On Friday, October 7, 2016 at 12:19:03 PM UTC-4, CyScape wrote:

Stay safe Dan!

[peter wolsley]

Dan,

I always uses 50% autoguiding rate on my CGEM.  When you post your guiding log please make sure it contains your PHD calibration.  We should be able to confirm that 99% autoguide rate is truly giving you 99% rate.

Peter

[BigDan]

Here is my guide log and debug log from Sunday October 9. I did 4 x 5 min. sub.'s each for LRGB.  There was a constant 10 MPH wind that gusted at times.  My polar alignment will get better when my POD arrives, as I'll have a permanent pier mount and really dial in the polar alignment.  I ran Guiding Assistant for 120 sec. up front.  It did not give me a message that my polar alignment was super bad.  The main thing I'm happy about is that the ASCOM driver is working with the CGEM.  I believe that the mount is well balanced with counterweight.  Autoguide Rate in the Celestron HC was set to 99%.  Let me know your thoughts.

[peter wolsley]

Dan,

Your polar alignment was probably good but there were so many DEC backlash movements that it's hard to tell.  I see backlash movements that are roughly 45".  My CGEM has 50" of backlash.  I have found that perfect polar alignment is not a good choice for my CGEM.  I find that DEC calms down with virtually no backlash movements if I have roughly 3' to 4' polar alignment error.  I also use hysteresis guiding for DEC with 90% hysteresis and 70% aggression.  These settings causing PHD to send very small but frequent pulse guiding commands to DEC that tend to always be in one direction.  This seems to avoid triggering a backlash movement.

PEC looks to be roughly 20" peak-to-peak.  You need to train your mount's PEC.

Your pixel scale is not great.  15.26"/pixel is very course.  I think this explains why your RA guiding is so noisy in spite of the fact that your SNR is over 200.  You should run the guiding assistant for much longer so that it can calculate more information.  Consider increasing the focal length of your guider so that the pixel scale can be reduced.  My guider has a pixel scale of 6"/pixel.  Many PHD users have guiders with pixel scales between 1" and 2"/pixel.  Another idea to consider would be to off-focus your guider.  I suspect that PHD is trying to perform it's star centroid calculation with far too few pixels.  Slightly off-focusing the guider should spread some of the starlight onto adjoining pixels which may make the centroid calculation more stable.

The PHD calibration indicates that you are getting close to 100% autoguiding rate so ASCOM seems to be working correctly.

Bruce and Andy are the PHD masters. I look forward to read what their suggestion are.

Peter

[bw_msgboard]

Hi Dan.  Just when I thought I’ve seen everything, along comes something new. <g>  I’ve never seen anyone trying to guide at a focal length of 100mm and an image scale of over 15 arc-sec/px.  Jeez.  This is really not a good plan IMHO.  Even assuming the star position calculations are accurate to 0.1px (the centroid algorithm), that would still result in uncertainties of 1.5 arc-sec.  That’s a large margin of error unless the image scale on your main system is equally huge.  You’ve got a nice guide camera but it has fairly large pixels, so I think you should get yourself a decent guide scope, something more like a 300mm focal length. What is your main imaging set-up?

 

Beyond that, it’s usually not practical to analyze guiding performance in 10 mph winds.  We can see you have large, abrupt excursions in RA of 5-7 arc-sec, and excursions nearly that bad in Dec.  Is that wind or something else?  We really can’t know.  As Peter suggested, you should run the Guiding Assistant for an extended period of time, maybe 10-15 minutes, so we can see what the mount is really doing.  You should absolutely apply periodic error correction, there’s no reason not to.  You should also disable Dec backlash compensation at this point until you have a much better picture of what the mount is capable of doing.  But try to choose a decent night with at least average seeing to do the next set of measurements.  Imaging and guiding require patience, something most of us have in very short supply. <g>

 

Good luck,

Bruce

 

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From: open-phd...@googlegroups.com [mailto:open-phd...@googlegroups.com] On Behalf Of BigDan

Sent: Tuesday, October 11, 2016 11:35 AM
To: Open PHD Guiding

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[BigDan]

Thanks very much for the responses, gentlemen.  I'm in agreement with training my drive for PE..... need to get to that, I even downloaded Celestron's averaging program for training sessions.  Yes, some of the large spikes were wind gusts.  I agree that the guide scope is a short focal length....... the small guide scope comes with the SBIG guiding kit.  It was supposed to be absolutely fantastic for my 8 in. SCT. 

 

This will all become a moot point, however, because my POD is supposed to be shipped at the end of October, and I will be setting up my Losmandy Titan on permanent pier...... the Titan will be my primary imaging mount.  I'd like to think it has more accurate guiding capability than the CGEM. 

 

So, all these things will be improved:  Polar alignment, PEC training, and look into longer focal length guide scope.

 

Thanks.

 

Dan

[BigDan]

 

One other thing I'd like to mention about jumping to the longer focal length guide scope:  I've seen scopes like the Celestron that is 600 mm, but it is f/7.5.  My little guide scope is fast, at f/2.8.  Wouldn't that mean that I can see more stars, and they would be brighter, giving more guide star possibilities?  And obviously because of the small size, it is lighter.  If the 100 mm is causing huge errors, I'll go for the longer focal length.

 

On the new imaging train, with the Titan, eventually I'll go with ONAG, and use the imaging OTA for the guide scope.

 

For 5 min. sub.'s, the 100 mm may work.  If you guys think the Celestron 600 mm at f/7.5 will noticeably improve the guiding on the CGEM/8 in. SCT, I'll try it.

[bw_msgboard]

It sounds like you’re in the middle of a big transition so you may not want to waste time and money on stopgap solutions.  Based on secondhand experience and looking at logs, I think you’re likely to get much better results with the Losmandy Titan mount.  The Celestron refractor you’re talking about sounds like it might be long and heavy, so differential flexure could be a problem.  As for the ST-I kit, I think it’s not a very good solution unless you are doing low-resolution imaging.  The SBIG claim is that it is capable of one arc-sec guiding, which is frankly not all that good if you’re trying to image with longer focal lengths.  Yes, it will have lots of guide star choices but the problem is the low resolution – you would be operating in a very marginal area in my opinion.  I think you’ll have to evaluate your situation once you have your SCT running on the better Losmandy mount and then decide whether you want to use an OAG or a guide scope.  The OAG is probably preferable because of the mirror shift in the SCT and the numerous sources of mechanical deflection.  But of course an OAG makes it somewhat harder to find guide stars and may require that you rotate it to get a decent guide star.  If you decide to try a separate guide scope, try to get one that will put you at a guider imaging scale in the mid-single-digits.  Also, you’ll need to be sure it is fairly compact and rigidly assembled, and the connection to the SCT will need to be equally rigid.  Differential flexure will always be a factor but you may be able to side-step it to get sufficiently long exposure times.  Unfortunately, you won’t be able to know until you have it in place and running.

 

Good luck,

Bruce

 

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[BigDan]

 

Thanks for the feedback.  I went ahead and ordered what I'm hoping will be an upgrade and replacement to the SBIG 100 mm guiding lens.  Maybe it's cheap junk (the guidescope), but I'll try it.  I ordered an Orion 400 mm focal length, f/5, 80 mm aperture short scope, and separately ordered the Losmandy 3 ring guidescope mounting kit.  Two rings to hold the guidescope, one to hold the camera.  Differential flexure concerns me, but I've tried OAG in the past, and basically decided the disadvantages for me outweigh the advantages.  I want to enjoy this hobby, without being exasperated.  I have a C14 that will go onto the Titan mount.  The initial imaging with it will be Hyperstar.  But before I purchase the Hyperstar lens,  I intend to use the 8 in. SCT for a while on the Titan.  If this new guidescope improves my guiding..... fantastic.  I think my current guiding setup would work with Hyperstar on the C14.  After that, in the long run, I will go large format/rear cell imaging on the C14, with ONAG.  Gaston Baudat told me my mono SX-694 would work great as a guide camera on the C14 when using large format imager with ONAG.

 

I'll try the new longer focal length guidescope.  If I feel my charts noticeably improve, I will post some more logs.

 

Thanks very much.