Star Trails even when tracking over 60 seconds

[m0pxs]

Hi newbie here,

I set up my new HEQ5 last night to get to grips with it, I polar aligned it via NINA successfully and thought I would have a go at the Pinwheel galaxy through my WO Z61, well I found it, centred it (using plate solving) and took a few test exposures using ASI533MC Pro, firstly at 30 seconds and 45 seconds all was fine, but at anything over a minute and there were various star trails, I checked eqmod and it was in sidereal mode and stated it was tracking. I then thought I could use PHD2 on my guide scope and AIS120MM Mini to clean things up, but it wouldn't calibrate and eventually when it did it appeared not to be able to make sufficient adjustments to keep things guided and then it just gave up. I eventually went on to image at 45 seconds for multiple subs and the result when stacked weren't bad, but anyone got any ideas why I can't get it to track properly either without PHD2 or even with PHD2 (I haven't adjusted any setting in PHD2), the scope is balanced in both RA and DEC.

In anticipation,

Phil

 

[m0pxs]

Extra,

It must have been tracking fairly well as the subs were all exactly centred and this was done over a period of 30 minutes

[m0pxs]

This is one of the 3 minute subs, the trails are top to bottom, whereas the 45 sub is perfect with perfectly round pinpoint stars. I know this one is of Bode's

Edited May 28, 2022 by m0pxs
additional info

[ONIKKINEN]

You are experiencing periodic error in the RA axis since the trailing in your example is in that direction.

Periodic error exists in basically all equatorial mounts and is the number 1 reason why people generally use some kind of autoguider, and by doing so the problem is fixed.

If you dont want to guide you need to shoot exposures that are short enough to not be effected by periodic error. What length that is depends on the mount, target DEC, pixel scale and how much trailing you deem acceptable.

Since you noticed the error when shooting M81, a very high DEC target (and so moving slower through the sky = less apparent trailing than at lower DEC) it looks like you have quite a lot of periodic error. Solution is to shoot shorter subs or guide.

[michael8554]

Ahh, so the image is M81,  no wonder I couldn't find that edge-on galaxy on the chart around The Pinwheel :-<

As ONIKKENEN said, Periodic Error, try shorter exposures, or guide.

Your PHD2 problems are nearly always due to incorrect equipment settings, so post your GuideLog.

From the PHD2 folder, make sure the date in the file name is relevant.

Michael

[Starflyer]

In EQMOD make sure you set the guide speed to 0.5 to 0.8, then in PHD2 use the wizard to setup your equipment profile. These two things, in this order, should make your calibration succeed.

Always calibrate PHD2 on the celestial equator, just before the meridian. There's a very simple cheat to make sure you're calibrating there, choose Tools - Drift Align from the menu, choose Slew, let is slew and then close the dialogue box.  This will always get you to the ideal place in the sky to calibrate.  This all assumes you're using pulse guiding and not ST4 guiding.

Good luck and let us know how you get on.

Ian

Edited May 28, 2022 by Starflyer

[m0pxs]

3 hours ago, michael8554 said:

Ahh, so the image is M81,  no wonder I couldn't find that edge-on galaxy on the chart around The Pinwheel :-<

As ONIKKENEN said, Periodic Error, try shorter exposures, or guide.

Your PHD2 problems are nearly always due to incorrect equipment settings, so post your GuideLog.

From the PHD2 folder, make sure the date in the file name is relevant.

Michael

Here is the guidelog file, don't really understand what it means though. 

If it is PE why does it not affect the centering of the object over a long time (in excess of 30 minutes) as in my subs schedule when I eventually elected to image the pinwheel, as this stayed centred but still produced star trails when exposure times exceeded 45 seconds. Or am I missing something about periodic error ?. Thanks for your help so far.

PHD2_GuideLog_2022-05-27_104937.txt

[michael8554]

PHD2 beginner's problems.

The ASCOM GuidePulse setting in EQMOD has been left on the default.

RA Guide Speed = 1.5 a-s/s, Dec Guide Speed = 1.5 a-s/s

Should be at least 7.5arcsec/sec.

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

So PHD2 aborted most of the Cals after 61 Cal step , should be about 12.

Cal was at Dec = 45.3 deg,  best to Cal at near Dec = 0 and near south.

Once you have a good Cal you can use it all night on all targets.

RA and Dec seem to moving in the same direction, instead of at 90 degrees to each other - cable problem ?

I get the impression you haven't read the Instructions available via the help menu ? 

Michael

 

[m0pxs]

14 hours ago, michael8554 said:

PHD2 beginner's problems.

The ASCOM GuidePulse setting in EQMOD has been left on the default.

RA Guide Speed = 1.5 a-s/s, Dec Guide Speed = 1.5 a-s/s

Should be at least 7.5arcsec/sec.

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

So PHD2 aborted most of the Cals after 61 Cal step , should be about 12.

Cal was at Dec = 45.3 deg,  best to Cal at near Dec = 0 and near south.

Once you have a good Cal you can use it all night on all targets.

RA and Dec seem to moving in the same direction, instead of at 90 degrees to each other - cable problem ?

I get the impression you haven't read the Instructions available via the help menu ? 

Michael

 

TBH I got a little confused with the online instructions so thought I would watch youtube, but obviously they assumed a lot too, when I get another clear night I will carry out your suggestions now I have read into them and understand them. All cables appear to be fine as I appear to have full computer control; of the mount in all other respects. Thanks for your help

Phil

[Fegato]

19 hours ago, m0pxs said:

 If it is PE why does it not affect the centering of the object over a long time (in excess of 30 minutes) as in my subs schedule when I eventually elected to image the pinwheel, as this stayed centred but still produced star trails when exposure times exceeded 45 seconds. Or am I missing something about periodic error ?. 

 

Just to answer this - periodic error relates to small errors in the RA worm gears. They go in a cycle - so you will tend to end up in the right place, but in effect the stars are moving up and down creating the trails. As explained Guiding will correct for this. 

re: PHD2 - worth spending some time understanding the basics, and key thing - never use a calibration if you get any error messages. Try and work out what the problem is and fix it, then re-calibrate. Running the Guiding Assistant is a good idea too.

[Adam1234]

Also worth checking that the equipment details (focal length of guide scope, focal length of main scope etc) are correct in the equipment profile

[m0pxs]

Well thanks for your kind assistance, after following your guidance all is now sorted.