PHD2 Guiding advice

[Celestron4]

 I am using an Altair GP-CAM AR013 OC colour camera (which I realise may not be ideal) with a 60mm guidescope. I have ben able to get up to 3 minute exposures without star trailing becoming an issue but am struggling to get the guiding to allow for longer exposures. I have attached my settings and a log file from last night. My target was M101  but ave had the same problem with M42, M51 and M81. Any advice?

PHD2_GuideLog_2020-05-20_221618.txt

[michael8554]

Your Calibrations were getting better as the night wore on, but were spoiled by the huge Dec backlash - 15 steps, one every 2 secs, means 30 seconds to reverse Dec direction.

So although your RA guiding was thereabouts in the last session, Dec was struggling.

Your Guide Rate looks quite low, about 5arcsecs/sec, you should up this in the mount to maybe 12arcsecs/sec / 90% / 0.9 of Sidereal, which will help PHD2 to move the Dec axis.

So what mount ?

What main scope ?

How are you balancing ?

PHD2 is up to Version 2.6.8, your 2.6.5 is 2 years old.

Don't delete the old version, just run the installer for the new version.

Check in the PHD2 Mount Settings that the new Guide Rate is being shown.

Focus is poor, HFD = 5.76, use the Star Profile window to get HFD down to 3 to 4.

Before Calibrating, nudge the mount north at lowest slew rate until you see the star move, to take up the Dec Backlash.

After a successful Cal, run the Tools / Guide Assistant, this will work out the Minimum Move settings you need. 

Do this routinely each night before guiding on a target to get the best settings for the conditions.

First time round maybe leave Measure Backlash ticked, but it will probably fail, so next time leave it unticked.

Read these Best Practices notes from the PHD2 developers:

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

Make some changes and post your new log including a Cal and a Guide Assistant run.

Michael

 

 

 

[Celestron4]

 Thanks very much for the advice! I have a Celestron AVX mount and my main imaging scope is a Celestron Nexstar Evolution 6 SCT. I tend to balance the setup with the imaging camera (Canon DSLR) attached if this helps.

[michael8554]

Depends on your next guide log, but I think you will need to be creative with your balance to prevent Dec changing direction, your PA is good so Dec should only need minimal guiding corrections.

Michael

[Celestron4]

Just realised that the Guidelog shows every time I stopped and restarted the guiding. The goto system on my mount wasn’t being helpful (M101 was just outside my camera field of view and took some fiddling to get it right. My calibration was done in the area of the target. Is this best or should I be using a bright star near the pole?

[michael8554]

With your ST4 style cabling,  PHD2 cannot get a reading of the mount's RA and Dec position, so you should always Cal on your target, and every time you change target.

ASCOM type cabling gives PHD2 the RA and Dec, so you do one Cal pointing south at Dec 0, and use that one on every target, every night.

Dec 0 is used because that's where the stars appear to move fastest in RA.

PHD2 will then compensate for the smaller amount of RA guiding needed the further you go up in Dec.

Michael

[Merlin66]

Michael,

Not correct.

you can add your mount as the “Aux mount”- I use this with my Lodestar to guide my C11 on the NEQ6PRO.

No issues.

 

 

 

[michael8554]

6 hours ago, michael8554 said:

With your ST4 style cabling,

I deliberately used that wording as in this case he isn't using Aux mount .

Page 3 of the PHD2 Best Practices that I gave a link to advises an Aux mount connection - so already covered thankyou.

Michael

[Celestron4]

I have been using the on-camera connection. Is this part of the issue?

[michael8554]

Well that Aux Mount connection doesn't appear to be working, according to the Guide Log.

But it shouldn't impact on your guiding if you follow the rules of Calibrating and Guide Assistant runs on target.

Something for later, after you've improved focus, upped the Guide Rate, and got good Calibrations.

Michael

[Celestron4]

Finally got a clear night. Set up the scope and AVX mount as before and connected to PHD2 using the on-camera connection. I ran the Guiding Assistant as you said and I have attached the results below. It shows that my polar alignment was slightly off even though I ran the polar alignment tool on the mount which usually gets me quite close. I have also attached one of my 3 test images (I take them in raw form but have converted it to .png for ease of upload) which should show the issue. Its close but not quite there. Any ideas?

PHD2_GuideLog_2020-05-28_232456.txt

[michael8554]

Your third Cal at 23:50 was getting there, with the axis at 90 degrees to each other.

But you didn't nudge the mount north until the star moved, as mandated in the Best Practices PDF, to clear Dec Backlash before Calibrating.

So there were 45 Backlash Correction steps that muddied the Calibration

So better Cals are possible.

Your image results are pleasing, but there are a few problems remaining.

Polar Alignment Error wasn't just slightly off, it was 18 arcmins, try to get it down to about 5arcmins.

Periodic Error on RA is large, you could investigate Periodic Error Correction for the mount.

 

You can see from this RA trace above that the guiding error was always above the line, with constant guide east corrections, PHD2 never got the guiding to centralise on the zero line.

 

Dec is similar, always below the line.

Both these drifts are in part due to the PA and PE errors. Both RA and Dec Aggressions having high settings, but PHD2 isn't managing to totally correct the drifts.

PHD2 calculated Guide Rates are still low despite recommendation,  increasing both to 0.90/90% of Tracking Rate in the mount, this will allow PHD2 to make bigger corrections.

Finally there are some strange movements in Dec that aren't due to PHD2 pulses.

Just before points A, B, C, PHD2 has corrected with the PHD2 north pulses, but the mount immediately moves south on its own to where the arrows point, there is a gap in the PHD2 guide pulses where this occurs.

This action repeats for a long time. 

Have you got Backlash Compensation set to ON in the mount?

This will fight against PHD2 as you can see, turn it to OFF and use the PHD2 Backlash Compensation offered in the Guide Assistant results.
 
Michael

[Celestron4]

I've had a look at the mount. The Backlash compensation seems to be set to 0 for both Dec positive and RA negative as you can see. I have also attached the settings showing RA and Dec Indexes and the Cone value if these help. I used the settings recommended by the Guiding Assistant on PHD2 which may have lowered my tracking rates. I leave them out tracking the object while it calibrates. Its seems to work fine for 3 minutes but problems occur at around 5 mins. I have the guide camera set to 2s exposures which seems to work. I will change the tracking rates to 0.90 on the hand controller see if that makes a difference. 

[Celestron4]

The polar alignment tool on the mount works quite well most of the time and have not had to move my alignment at all when I use the tool within PHD2. I will try using the tool in PHD2 rather than on the mount and see if this makes a difference.

[Celestron4]

Had another go. I have attached the new guide log and guide assistant page. I used the PHD2 polar alignment tool which seemed to help improve my alignment. I managed to get some just about usable images such as the one attached below. Moving in the right direction and getting closer!

PHD2_GuideLog_2020-05-30_000728.txt

[michael8554]

Much better.

Calibration was better this time.

RA and Dec are now moving about the X axis.

PA is still 18arcmins, but Dec is now also moving about the X axis with hardly any correction needed, so good enough.

Calibrations would be a lot more accurate for PHD2 to guide with if only you'd nudge Dec north until you see the star move, before you Calibrate.

Michael

[Celestron4]

Thank very much for your help so far! I have attached the data from a few nights ago. I used the manual guiding tool in PHD2 to nudge the mount north before calibrating which seemed to reduce some of the north movements. The log file shows 'guiding stopped 03.06.2020. My DSLR imaging camera died and caused both PHD2 and Astrophotography tool to crash and have only just managed to close them properly. 

 

 

PHD2_GuideLog_2020-05-30_121318.txt

Edited June 3, 2020 by Celestron4
Correcting the uploaded images

[michael8554]

Some on SGL say you should forget the data, look at the images.

Your last two images are very similar in terms of the amount of star elongation, despite our best efforts !

As shown by RA RMS being 50% bigger than Dec.

Final adjustment would be your Guide Rate, which is 5 to 6 arcmins/sec on both axis.

That's quite low, the PHD2 guys recommend at least 50% to 80% of Sidereal, about 8 to 12 arcsecs/sec, I'd try 12.

Your Guide Assistant results would be more consistent if you guided for about 30 seconds until the mount settles down, then hit the Start button on Guide Assistant.

Are you sure you're nudging north until you see the guide star moving north, before Calibrating?

There were 10 Clearing Backlash steps before Dec Calibration started at 00:39 ?

Michael

[Celestron4]

I used the manual guiding on PHD2 to move it northwards (basically held the north button) until I saw the star move. I will try using a faster guide rate see if that works!

[Celestron4]

Finally managed to have another go with PHD2 last week. I have attached the Guide Assistant readout and log file. along with another test image. The polar alignment seems to have been quite good and the mount was nudged north until the star visibly moved before calibration. I have also upped the guide speed to 0.8 and subsequently 0.9 but I still seem to be getting star trails with 5 minute exposures. Any ideas as to why?

PHD2_GuideLog_2020-06-24_224627.txt

[Celestron4]

The test image is not ideal. It was a very warm night (DSLR sensor temperature showing as 30 degrees on Astrophotography tool) and close to the Solstice so quite light and very noisy

[newbie alert]

On 29/05/2020 at 15:32, Celestron4 said:

The polar alignment tool on the mount works quite well most of the time and have not had to move my alignment at all when I use the tool within PHD2. I will try using the tool in PHD2 rather than on the mount and see if this makes a difference.

Are you using the ASPA on the AVX..

I'd run the guiding assistant for far longer than 203 secs, try a full worm period

[Celestron4]

I have used the Polar alignment feature in the past and it has got me quite close but I didn’t use it this time as the polar drift alignment tool on PHD2 required little adjustment (the required star position (red circle) was within the green square). I ran the Guide Assistant until the numbers for Right Ascension, declination. And polar alignment had settled as is stated in PHD2 when you run the tool. 

 

 

[michael8554]

I agree with Celestron4, the guidescope Signal to Noise was very low, and that was probably the cause of most of the choppy RA.

At one point you guided for 8 minutes on a Hot Pixel !

I would disable Star Mass Detection and instead set the Minimum HFD to 2.5.

Otherwise, good Calibration.

PA was 9.3 which is a tad high, about 5arcmins would be quite useable.

You could improve your guidecope focus, 4.57pixels, use the Star Profile in PHD2 to get the HFD to a minimum, ideally between 3 and 4.

Your mount connection doesn't tell PHD2 the RA and Dec position, so you will have to Calibrate on every new target.

Michael

[newbie alert]

15 hours ago, Celestron4 said:

I have used the Polar alignment feature in the past and it has got me quite close but I didn’t use it this time as the polar drift alignment tool on PHD2 required little adjustment (the required star position (red circle) was within the green square). I ran the Guide Assistant until the numbers for Right Ascension, declination. And polar alignment had settled as is stated in PHD2 when you run the tool. 

 

 

I'd try running the guide assistant for a full worm period

I'd guess that you're doing the same thing with the drift tool, adjusting far too soon..

Olly posted something a few weeks ago that should work really well, but I've not tested it yet

https://www.cloudynights.com/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760