IEQ45 Pro and PHD2 OAG Guiding issues

[waylander]

Hi everyone,

 

Now i seem to have more time to image i bought myself a ZWO OAG to use instead of my 50mm Guide scope. Main scope is 80mm altair ED doublet, ZWO 290mm guide cam. My mount is on the heavy duty pier.

Unfortunately i'm not able to get a successful PHD2 calibration no matter what i try.

My guiding has never been great -  usually 1.3" RMS with the guide scope no matter how good my PA was, so i thought perhaps i could get some improvement using an OAG - and also not have to set up the guide scope, dew heater, balance it etc. OAG set up was quite easy, focusing accomplished - "awesome" i thought, that's the hard bit done 

I started with a new profile, put the main scope focal length in (454) and hoped for the best. Now it must be said i rarely do any form of polar alignment - I generally just align north and be done (slack i know) because i have found it not to make that much difference. I've been getting orthogonality errors for almost every cal run (i tried altering guide rates to see if that helped) - you can see in the attached log. 

 

1. From reading the PHD2 manuals this might be backlash? And if so should i just make sure i run the max guide rate to minimise this? Anything else i can do?

2. Why am i seeing errors now, it was "OK" with the guide scope? Why cant i even calibrate at all?

3. Will PA align make more difference with the longer focal length?

4. Will my mount need "fixing"?

 

Many thanks to everyone in advance,

Clear skies, stay healthy!

PHD2_GuideLog_2020-04-02_191021.txt

[ollypenrice]

Is this the version of the mount with the spring loaded worm gears? These can become very under-sprung after a while, leaving a lot of room for sponginess in the drive. It's not exactly backlash, which is free movement, but it's certainly a lack of stiffness. I think later mounts were made differently.

Olly

[waylander]

thanks - as far as i know this is the latest version of the mount - its a 2018 model.

[almcl]

A quick look at your guide log suggests that the orthogonality error (29° on the 1st run) is preventing a good calibration.  At least one estimate of your PA error is in excess of 25 arc minutes and it would definitely be worth reducing this and seeing if it reduces the ortho error.  Your polarscope should allow you to get within 5 arc minutes or Sharpcap or similar can do a reasonable job.

Once you have a calibration, running the guiding assistant and accepting its recommendations and then guiding for a reasonable period will show if there are any mount problems that need to be addressed.

[waylander]

Just now, almcl said:

A quick look at your guide log suggests that the orthogonality error (29° on the 1st run) is preventing a good calibration.  At least one estimate of your PA error is in excess of 25 arc minutes and it would definitely be worth reducing this and seeing if it reduces the ortho error.  Your polarscope should allow you to get within 5 arc minutes or Sharpcap or similar can do a reasonable job.

Once you have a calibration, running the guiding assistant and accepting its recommendations and then guiding for a reasonable period will show if there are any mount problems that need to be addressed.

Thanks almcl - ive used sharpcap previously to do the static polar align - i can try that again. Would this cause the issues visible in the cal log? Ive never seen anything like this with guide scope usage... is it just because of the longer FL?

[almcl]

Some of the calibrations look really strange:

  

 

And it may be that adjusting hysteresis, min move and aggression at random is contributing to this, although why the dec axis appears to move in the opposite direction to the RA in the second one is definitely a puzzle.  .  

From one of the more 'normal' calibrations it looks as though you need a calibration step between 250 and 500, but I don't think that is the major issue.

Did you do a new equipment profile when you switched to OAG?  Some parameters that are not directly visible to the user get altered in addition to the ones that have to be set in boxes and it may be worth redoing this, even if you already did one.

[waylander]

Hi mate, thanks for the info - yeah i did a new equipment profile unfortunately. 

When i get my next clear sky i will create another profile, do a proper sharpcap polar align and see what that gives me. I did notice that in some cal runs it seemed to be going backwards...  what confuses me is why now? If i go back to the guide scope i bet it works "fine" as before...

Edited April 3, 2020 by waylander

[almcl]

Just a passing thought, but is the OAG (and camera) absolutely securely nailed down?

[waylander]

I think so - i will double check both the oag imaging train threading and the guide cam in the little 1.25 holder on the oag

I should also point out i tried Metaguide, but this failed calibration too...

 

Also - i read the increasing guide rate can combat backlash - shall i use 1x guide rate? I normally stick to 0.5x.

Edited April 3, 2020 by waylander

[almcl]

If have a look over on the PHD2 wrbsite (https://groups.google.com/forum/#!forum/open-phd-guiding) and search for messages about your specific mount, you'll see some recommendations along the lines of '.5 is too low, try increasing it'.

[waylander]

2 minutes ago, almcl said:

If have a look over on the PHD2 wrbsite (https://groups.google.com/forum/#!forum/open-phd-guiding) and search for messages about your specific mount, you'll see some recommendations along the lines of '.5 is too low, try increasing it'.

thanks a lot for that - ill go through those now  Looking at the phd logs it certainly does seem the higher guide rate gives better results yes.

[ollypenrice]

The polarscope on the Mk1 iEQ45 I reviewed was very good. I'd certainly start with that.

Olly

[newbie alert]

The better your PA,  balance etc you get the better your guiding will be ..

But, your calibration is probrably the strangest that I've ever seen

[michael8554]

15 hours ago, waylander said:

Now it must be said i rarely do any form of polar alignment - I generally just align north and be done (slack i know) because i have found it not to make that much difference

That might have sort of worked for a shorter focal length guidescope, but you'll have to get PA down to about 5arcmins with the OAG.

Also check balance.

Turn off any Backlash Comp on the mount as it fights the PHD2 Backlash Comp.

Then see what your Calibration is like. Nudge north with the handset until you see the guidestar move, to take up the Dec Backlash, before you Cal.

Michael

[waylander]

Right. Just been out. Managed a 1 minute pa error. Set guide rates to 0.9x. Awful seeing tonight with a bit of high mist and 85% moon. Managed to calibrate properly! Guide at 1.3”rms. not many stars visible though so that’s ok for the conditions I think. Didn’t bother imaging due to conditions. But it seems to be sorted now! Thanks all!!

[michael8554]

Good stuff - let's see your Guide Log, such as it is, "for purely academic reasons of course"

Michael

[waylander]

 

Lessons learned:

1. Take cap off telescope when trying to do astrophotography...

2. Use a bahtinov mask, i was out of focus for both guide and main cam.

 

Seeing was bad last night - kept losing stars, so i upped the exposures... but even then the star choice was poor.

I did notice that my guiding is now going to have to be better than the above as my px error was around 1px. I used to get 0.5px when using the guide scope.

Any further tips willingly received.

Thanks all!

 

PHD2_GuideLog_2020-04-04_114733.txt

Edited April 5, 2020 by waylander

[michael8554]

A huge improvement.

Yes conditions didn't look good, so I wouldn't judge this guiding too badly, I would wait for a better night.

On the long guide session RA was 1.2arcsec, Dec was 0.73arcsecs RMS - not too shabby. Compare arcsecs not pixels.

PA is good.

Cal was carried out at Dec 54 instead of Dec 0, that higher Dec would flatter the results to an extent.

Shame you can't bin the guidecam, that would make the image scale 2.64arcsecs/pixel instead of 1.32, and would increase sensitivity, given the Star Lost messages you were getting.

Maybe try a cheap 1.25" screw-in reducer on the guidecam?

You can see in the Cal that the Dec North pulses come in pairs with gaps between the pairs, I've seen that before but can't remember the reason :-<

Dec was bouncing about, causing large Backlash Comp pulses in one direction, then the other. Maybe the seeing, but try balancing Dec slightly heavy in one direction.

RA has some Periodic Error, so try the PHD2 PPEC Guide Algorithm. Needs to relearn on every new night, so allow say 8 mins guiding to go through some worm cycles before imaging.

Try again on a good night with a Cal at Dec 0 and post the log.

Michael

Edited April 5, 2020 by michael8554

[waylander]

Michael i really appreciate the feedback - thanks for taking the time.

To get Dec 0 ill use my astro app on my phone, looks like as low on the horizon as i can get it in the south west. I know thats the phd2 recommendation - presumably if i calibrate there thats going to give me better cal? 

I'll also try PPEC (used that before too).

I'll adjust my dec balance too - pull the scope back a bit in the saddle.

As i say it was a bad night with some high level mist, i couldn't even find decent focus. 

One other issue i had is that i had to use my main camera with sharpcap for the PA as i could never get the 290m to solve - but im guessing thats prob just due to the bad seeing and therefore lack of stars.

I'll post back prob tomorrow night when its clear - gonna try some m101 but think it will be too bright with the moon even with my filter (optolong lPro).

Thanks!!

 

[michael8554]

2 hours ago, waylander said:

To get Dec 0 ill use my astro app on my phone, looks like as low on the horizon as i can get it in the south west. 

Can't you Cal at close to south and Dec 0 where you are? Orion straddles Dec 0.

Dec 0 is where the stars "move" the fastest, which tests PHD2 the most.

After Cal it will adjust as you move to higher Dec.

Dec 0 is about 40 degrees above the horizon where you are, pointing south at 21:00. Just ask the mount to slew to Dec 0.

I've realised now that your Dec 54 Cal must have been pointing almost straight up to the zenith if you were pointing south! (54 + 40 = 94 degrees) !

MichaEL

 

Edited April 5, 2020 by michael8554

[waylander]

Don’t think so - South is blocked by my house unfortunately. Can do south west though. Will give it a go tomorrow. 

[waylander]

Ok managed to do some imaging last night - they aren't really usable as it was almost full moon (not enough contrast).

Tried to calibrate at DEC 0 but too many clouds so had to shift it around a bit higher. Still kept losing guide stars - but again the seeing wasn't great and i struggled to get decent focus with either camera.

Tried an imaging run of M101,  guiding was initially around 1.3arc sec, but later on in the night after id enabled PPEC and tweaked the settings i did see my guiding get down to 0.7-0.8 for a while. RA seems worst, need to tame it, hence changing the settings a bit - tried to get the OSC value to 0.5.

I should also point out the calibration wasn't great - phd2 warned me to do it again as it was sub-optimal. 

I also noticed after going through the logs that my guide rate had reverted to 0.5x, so next time ill put that back to 0.9 which would improve the backlash situation and obviously guiding in general.

Any focusing tips very welcome - i find that the hardest thing of all - tried the bahitnov mask but it just kept jumping between + and - values.

Here's the guide log:

PHD2_GuideLog_2020-04-06_204427.txt

Edited April 7, 2020 by waylander

[Davey-T]

Just a thought have you checked it mechanically, particularly the screws holding the worm motor assemblies down, the dec ones on my older version came loose giving erratic guiding.

Dave

[waylander]

I havent - is there a guide on how to do this? Im completely allergic to hardware... completely inept!!

 

 

[Davey-T]

31 minutes ago, waylander said:

I havent - is there a guide on how to do this? Im completely allergic to hardware... completely inept!!

 

 

Video here, just remove the cover 2mm key I think, then drive it back and forth to check there is no movement on those two allen head screws each side.

Dave

https://www.youtube.com/watch?v=eXOuiaCxFd0

 

Edited April 7, 2020 by Davey-T