Paramount ME guiding issues

[John Cangelosi]

Hello,
Here is the BACKGROUND: I'm a teacher at a high school and we have an observatory on site that functions as an instructional aid for astronomy classes and an imaging resource for an astrophotography club.
We use a Paramount ME and a Newtonian with an FL of around 2100mm. We've been using TheSkyX for years for all our imaging, guiding, etc. but I'm in the process of transitioning to NINA to make everything more accessible to students- and to extend our remote imaging capabilities.

Here's the ISSUE: When using PHD2 in conjunction with NINA I'm getting some strange results that are even affecting focusing. For example, last night I was trying to focus through NINA and kept getting failures. When I switched back to TSX guiding it focused fine. Also my PHD2 guide graphs look very strange and there seems to be a lot of gross correction as compared to when I use TSX. We have recently done a complete recalibration through TSX, accurate polar alignment, and have run the PHD2 guide assistant.  I'm sure I'm missing something obvious but any help would be greatly appreciated so we can get running remotely. 

I did my full calibration and PA on 4/13/2023 so one of my PHD2 runs is before that (with guide assist- some may have been cut short) and then a couple after. My most recent is last night (without guide assist but did force a recalibration)[5/9/2023]. 

https://openphdguiding.org/logs/dl/PHD2_logs_CtL3.zip

Thanks, 

John

[mj.w...@gmail.com]

Hi John

Not one of the experts, so I hope they will be along to fill in the fine detail.

The 2450mm Focal Length in the settings suggests you were guiding with an Off Axis Guider ?

1) The last Cal on the 4th February was poor.

ortho.err. = 70.2 deg,

Should be close to zero deg.

Which meant any guiding since then had RA and Dec corrections in almost in the same direction, instead of being 90 degrees apart !

Which PHD2 will have warned whomever last Calibrated PHD2 ??

And would have shown on the toolbar by "Cal" being red instead of green, every time guiding was attempted 

2. After a good Cal on the 9th May, seeing was so poor that the OAG camera output was extremely erratic.

Which reflected into the guiding.

Michael

Wiltshire UK

[John Cangelosi]

Thank you for looking at this Michael.

1. Yes it is an OAG and everything before April 13 should be pretty bad (but probably not that bad!)

2. As for the seeing, that makes sense but I'm wondering why the Sky's autoguider did not have an issue.

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John Cangelosi
Science, Technology, and Engineering
Bangor High School

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[Bruce Waddington]

I have a bunch of family obligations today but I will get back to this tonight and let you know what’s going on.  We have lots of Paramount users so obviously there’s a way to make this work.

 

Cheers,

Bruce

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[Bruce Waddington]

Hi John.  I think you should probably take a different approach to get this sorted out.  I know your objective is to transition to NINA and PHD2 is just “along for the ride", but I think you should spend some time learning how PHD2 works and getting the guiding situation under control without using NINA – just run PHD2 by itself.  Since you’re a teacher, I will assume you’re accustomed to doing some reading to learn how things work – here are two good references, the User Guide and our Best Practices presentation:

https://openphdguiding.org/man-dev/ (for the latest PHD2 dev release)

https://openphdguiding.org/phd2-best-practices/

 I think the thing that is causing you the most trouble at this point is that you need to check the box for 'Reverse Dec output after meridian flip':

The meridian flip might be implicit in the sense that you start guiding in a session while using a calibration from an older session that happened to be done on the opposite side of the pier.  The latest version of the SB driver software requires this option to be set.  While you're working through the basics of getting guiding to work well, it's a good idea to start each night's session with a fresh PHD2 calibration.  You don't have to keep doing that, it's just a good thing to do when you're in trouble-shooting mode.  Do the calibrations near Dec = 0 and within 15-20 degrees of the celestial meridian. 

I'm not familiar with this guide camera you're using but it doesn't seem to be capturing many guide stars even with long exposures.  Are you in a heavily light-polluted area or dealing with poor transparency?  Unattended automated imaging works best if you can get guide stars anywhere in the sky.  That usually translates into a larger sensor and higher sensitivity than what you may have. You are using long exposure times already which then makes the calibration process somewhat more challenging.  Typically, we recommend 2-sec exposures for that process but only if you can get acceptable guide stars.  Another option would be to try binning the camera - but if you decide to try that, be sure to use the PHD2 new-profile-wizard to create a new profile with your choice of binning.  Configurations with different binning factors should be kept in separate profiles.

If you want to do a thorough job of getting a solid baseline for the guiding, you can follow this procedure:

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

Although this may seem like a diversion from your main objective, I think you will, in the end, waste less time and get better results if you get PHD2 working well with your mount before layering on the additional complexities of NINA and image automation.  As a final note, PHD2 has nothing to do with focusing but with an OAG, it's important to pause or stop guiding during a focus run.  We'll be glad to help you out with log analysis as you move ahead.

Good luck,

Bruce

[John Cangelosi]

Thank you Bruce, I will follow your advice regarding PHD2 as a separate application and I'll have more time to dedicate to this in a few weeks. 

I've checked the Reverse Dec Output after flip option- so all set there. 

And on my next use I'll calibrate first and in the proper area to see how that goes.

As for my camera, it is an SBIG OAG. I'm no expert but from what I read people seem to be happy with its performance but I am in a small city with plenty of light pollution and probably the logged nights were not under the best conditions. In addition, the position of my AOG chip on either side of my target (mostly the Needle Galaxy lately) shows a small number of stars to use on opposite sides of the meridian flip (from what I see in my SkyX image link- could be wrong). So hopefully that will improve with other targets or just using one side of the pier. 

And I'll create a new profile - I usually bin 2x2 but should I go more?

Lastly, I've been guiding while focusing so I'll take care of that too. 

I really appreciate all the help!

-John

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[Brian Valente]

John

have you considered adding a rotator for keeping your guidestars in the OAG while doing a meridian flip? That's a typical solution for setups with long focal lengths and small apertures such as yours

regarding more binning, what is the image scale for your imaging setup? I suspect bin 2 is probably the best in terms of relative image scale compared with your imaging scope. You can try bin 3 and if you can get more guidestars and still maintain good guiding, that could work

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Brian 

Brian Valente

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[John Cangelosi]

Thanks Brian, I will look into the rotator and try to get one into next year's budget. I can now see how it would be incredibly useful after trying to plan out framing along with stars on opposite sides of the main camera- frustrating!

My image scale (I usually bin the main camera 2x2)  is 0.913 arcseconds/pixel. 

-John

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[Brian Valente]

>>>My image scale (I usually bin the main camera 2x2)  is 0.913 arcseconds/pixel.

if your bin2 guide camera is around 0.8, then bin 3 would be fine

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[Bruce Waddington]

I recommend that you do some more research before deciding that a rotator is needed.  A wheezy guide camera on a rotator is still a wheezy guide camera.  The available guide star candidates are few and far between during your sessions, usually one or at most two.  That's despite using long 4-5 sec exposures.  As I said earlier, perhaps this is due to bad sky conditions or maybe the guide camera isn't as well-focused as it could be.  I think it would be worth confirming this is really as good as you can do with your sky conditions.  That test should include temporarily discontinuing the use of your dark library - it's possible the dark library doesn't accurately reflect the camera properties.  When running tests like this, you can use the Diagnostic Image Logging functions on the 'Global' tab of Advanced Settings to capture a sequence of guide camera images.  Those can be brought into an imaging app so you can see what PHD2 sees and get a better idea of why the results are so sparse.  Finally, you should specify an ADU value for the option "Saturation by ADU value" on the 'Camera' tab of Advanced Settings.  The camera is running in 16-bit mode so the value should be in the neighborhood of 65K.

On the subject of image scale and binning, your guider image scale is being calculated as 0.81 arc-sec/px when binned 2x2.  That assumes a focal length of 2450mm which strikes me as an unusual value - did you mean 2540mm?  You could no doubt go as high as 4x4 binning without affecting your guiding results, especially if this would allow you to take better advantage of multi-star guiding.  Remember, when you start changing the parameters that affect the guider image scale, you need to be using the new-profile-wizard to do so.   Changing these values in the Equipment Connection dialog is intended for use by experts or for temporary experiments.

Good luck,

Bruce

[John Cangelosi]

I did some work last night and, although the conditions were less than ideal, I think there was some progress. 

I created a new profile for a 3x3 bin, created a dark library, positioned the scope at about 1 degree DEC and close to the meridian, recalibrated and ran guide assist for about 2 1/2 minutes. I did not follow all the steps in the dropbox resource because I was running remotely and had limited time so I'll save that for another troubleshooting session. I then went back to the Needle Galaxy just to compare to something recent and saw much better results. The signal was very weak due to a hazy sky so the star was lost a few times but when it engaged the performance was better- but I'm sure there is plenty  of room for improvement. 

 

Thank you for the advice regarding a rotator. It is possible that the camera is not perfectly focused and I'll go through the analysis steps you've outlined to try to get some information on the OAG. Just connecting now the Max Saturation setting is already correct (65535).

As for my focal length, I'll try to confirm but the scope was made by a former teacher here- decades ago- and donated to the school. It is difficult for me to accurately measure the FL but from what has been returned by image links and other comparisons it has been that 2450- although I could be way off here. Any suggestions on the proper way to nail that down would be welcome. 

Finally I'll attach my guide log from last night but when I do more work and maybe test in better conditions I'll upload that as well. 

Thank you! 

-John

https://openphdguiding.org/logs/dl/PHD2_logs_p4gq.zip

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[Bruce Waddington]

The easiest way to determine the focal length of the scope is to plate-solve one of your main camera images.  You can do that by uploading a full-res image to the Astrometry.net server:

https://nova.astrometry.net/upload

The plate solve process will return the image scale among other things.  Then you can calculate the actual focal length of the scope this way:

focal_length_in_mm = pixel_size_in_microns / image_scale

If you are binning the main camera, the pixel_size value should reflect whatever binning factor you used.

I'll look at your log files later today.

Regards,

Bruce

[Bruce Waddington]

Whoa!  Small omission of a constant in that equation - it should be:

focal_length_in_mm = (pixel_size_in_microns) / image_scale * 206.265

Too early in the day for me the first time around... :-)

Bruce

[John Cangelosi]

Got it! Thank you. 

= 2440 mm

(actually calculated 1220 mm but if binning 2x2 that should be doubled(?))

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[Bruce Waddington]

Yes, that’s right.  With 2x2 binning, your effective pixel size doubles on each dimension – 4 pixels are combined to 1 super-pixel.

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[John Cangelosi]

I'm wondering if my guiding with PHD2 is OK or could be improved? I followed the process in "How to create a baseline for guiding results using Open PHD2" and seemed to get a decent result during 'low altitude' imaging session last night. One thing that jumped out at me is; I did a calibration and then a guide assist but when I started imaging I noticed the calibration was gone or 'red'. Because the guiding seemed acceptable to my untrained eye, I decided to leave it as it was instead of doing another calibration. I've attached the log if anyone can take a look at it. 

Thank you!

-John

https://openphdguiding.org/logs/dl/PHD2_logs_6cCa.zip

[dolphi...@gmail.com]

well from what I can tell its better than my ME-II is doing right now - you have a small periodic frequency content at 50 seconds which I'm guessing is related to some event related to your captures (filter change or something like that ?) You might be able to slightly improve things if you turn on the PEC correction in the mount - since I see the 149.6 worm period I am assuming it is NOT turned on presently - I think it looks pretty good, I'd be happy if mine was like that all the time - the rms errors would be around a single pixel or less on my setup for my imaging camera

[bw_m...@earthlink.net]

I think the guiding looks fine, it looks like your results were limited by poor seeing conditions.  But the RA and Dec RMS values were similar so you should have been getting nice round stars.  Your calibration was fine and it was used for the subsequent guiding sessions so I don’t know what you were seeing.  The calibration icon may have gone to red during the course of the calibration but I don’t remember offhand if that happens.  If you hover the mouse icon over any of those icons, you will see an explanation of anything that is amiss.

 

Regards,

Bruce

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[John Cangelosi]

OK- that's good to hear. I don't have the PEC correction on right now but I plan to set that up soon. Thank you!

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