#1  
Old 04-10-2015, 01:00 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
PHD2 Polar Alignment issues

I use PHD2 for guiding but had not got around to seriously trying the polar alignment feature that it provides - drift align - until last night. I found a tutorial to try (https://sites.google.com/site/openph...rift-alignment) and over time I manage to get improvements - I think.

I could not get the red line to flatten very far at all, although the magenta circle became quite small. No matter what I did, the result was such that the RA was still jumping all over the place when guiding (+/- 2" easily).

I'm trying to work out why that was happening. I suspect the seeing has something to do with it, but trying with 1,3,5 sec guiding didn't seem to make much difference.

Would backlash cause this? What about the aggressiveness setting - I did have it at 100?

Finally, DEC seemed to be quite good compared to RA - hardly any movement.

My setup for this is as per my sig. I was at 2000mm - no reducer.

Thanks for any suggestions/help.

EDIT: I guess I should ask what information I could attempt to gather tonight that might assist in working this out? Is there anything I could try to eliminate some variables?

Last edited by lazjen; 04-10-2015 at 01:14 PM. Reason: More questions
Reply With Quote
  #2  
Old 04-10-2015, 01:04 PM
codemonkey's Avatar
codemonkey (Lee)
Registered User

codemonkey is offline
 
Join Date: Jul 2013
Location: Kilcoy, QLD
Posts: 1,702
Did you ensure you were pointing at the correct parts of the sky when doing this? A mistake I made which caused me some frustration. It's very important to point to the correct locations.
Reply With Quote
  #3  
Old 04-10-2015, 01:11 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Yes, I'm pretty sure. Although I did stuff around for a long time on this, so perhaps I moved away from the optimum area.
Reply With Quote
  #4  
Old 04-10-2015, 01:31 PM
RobF's Avatar
RobF (Rob)
Mostly harmless...

RobF is offline
 
Join Date: Jul 2008
Location: Brisbane, Australia
Posts: 5,460
Hi Chris, apologies if I'm stating the obvious, but you realise there is a different coloured line for Dec and RA? RA should show some noise, but also cycle over the worm reflecting the periodic error of your mount?

Dec gears have PE too, but generally once your aligned it shouldn't matter. As you get closer and closer need to drift longer to check it is correct.


Might be helpful to post up an image of what you're seeing if possible?
Others could then comment if seems normal for your gear.
Reply With Quote
  #5  
Old 04-10-2015, 02:02 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Quote:
Originally Posted by RobF View Post
Hi Chris, apologies if I'm stating the obvious, but you realise there is a different coloured line for Dec and RA? RA should show some noise, but also cycle over the worm reflecting the periodic error of your mount?

Dec gears have PE too, but generally once your aligned it shouldn't matter. As you get closer and closer need to drift longer to check it is correct.


Might be helpful to post up an image of what you're seeing if possible?
Others could then comment if seems normal for your gear.
I should have captured some screenshots last night, but I was a bit too brain fried to remember. I'll capture stuff tonight if I don't get it sorted.

As for the different coloured lines - yes that applies for the general guiding, but if you look at the tutorial page I linked, it uses the "red" line for the slope in the drift align process. You're suppose to "flatten" the line in the process and I was able to do so up to a point.

Periodic error will be in there since I don't have PEC enabled. I'll have to look up the value, but the mess I was seeing was quite frequent. Maybe it was having more of an effect than I thought.
Reply With Quote
  #6  
Old 04-10-2015, 08:38 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
I'm doing the drift align again now and I'm starting to think the periodic error is what I'm seeing.

Click image for larger version

Name:	phd2_snapshot2.png
Views:	67
Size:	28.3 KB
ID:	189082

I did drop the aggressiveness down to 70 from 100. I can't remember why I had it on 100 as I normally try for less.

I'll try to do a small adjustment to see if I can reduce the error further.

However, the RA line looks periodic.

Also, I'm pointing west, so I'll have to check east later. I have a suspicion the scope balance is affecting thing too.
Reply With Quote
  #7  
Old 04-10-2015, 10:03 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
There's definitely something wrong when I'm pointing east.

The first image was the last drift run in the west before flipping over. The second is the best east run so far - no azimuth adjustments made. All I've done so far is up the aggressiveness to 95 and balanced the weights towards the west - that seemed to help a bit. The variability though is a lot more in the east.

Click image for larger version

Name:	phd2_snapshot4.png
Views:	42
Size:	68.2 KB
ID:	189093Click image for larger version

Name:	phd2_snapshot5.png
Views:	51
Size:	31.3 KB
ID:	189094
Reply With Quote
  #8  
Old 05-10-2015, 08:11 AM
troypiggo's Avatar
troypiggo (Troy)
Bust Duster

troypiggo is offline
 
Join Date: Nov 2008
Location: Brisbane, Australia
Posts: 4,824
When drift aligning, you completely ignore the RA errors. Just watch the red DEC trendline. Doesn't matter at all what the purple RA is doing until you've finished drift aligning, have calibrated, and are actually guiding. You will see it flatten right out then.

I was doing some testing the other night, and I found it much easier to follow with the graph displaying pixels instead of arcseconds. Go into the settings button of the graph there, and choose pixels. Might be just the way I'm wired, but I found it easier, and the graph wasn't as spikey.
Reply With Quote
  #9  
Old 05-10-2015, 08:20 AM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Ok, I still thought the other line was showing how much "effort" was being done. I didn't notice that much difference to the RA line when I went to the normal guiding.

I found rebalancing helped a lot - and it was to the east not west as I wrote previously.

Still, I have to say the PHD2 drift align procedure seems to give good results and relatively quickly too. Following the process is easy and the feedback quick.
Reply With Quote
  #10  
Old 14-10-2015, 01:08 PM
Rod771's Avatar
Rod771 (Rod)
Turn the lights off!

Rod771 is offline
 
Join Date: Aug 2012
Location: Parklea NSW
Posts: 1,207
Hi Chris

I'm pretty sure PE cycles through every 8 minutes. Looking at your first graph your run appears to roughly finish around the 5 min mark? That would rule out PE as your major problem because you wouldn't see the RA graph rise and fall that many times in 5 mins due to PE.

I suspect seeing is your major problem, as it is for us all. Try a higher exposure time of 2.5 to 3 sec and increase the RA min move so you're not sending guide commands every exposure. This may help settle the RA down a bit.
Reply With Quote
  #11  
Old 14-10-2015, 09:40 PM
bugeater (Marty)
Registered User

bugeater is offline
 
Join Date: Feb 2015
Location: Mitcham, Vic
Posts: 313
I find getting the line nice and horizontal to be quite difficult too. It seems to change its trend periodically. Not sure if it is wind or something else.

But periodic error is a red herring - it can't be that as the line you are watching is the dec axis, not RA
Reply With Quote
  #12  
Old 16-10-2015, 06:42 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Quote:
Originally Posted by Rod771 View Post
Hi Chris

I'm pretty sure PE cycles through every 8 minutes. Looking at your first graph your run appears to roughly finish around the 5 min mark? That would rule out PE as your major problem because you wouldn't see the RA graph rise and fall that many times in 5 mins due to PE.

I suspect seeing is your major problem, as it is for us all. Try a higher exposure time of 2.5 to 3 sec and increase the RA min move so you're not sending guide commands every exposure. This may help settle the RA down a bit.
Thanks for the reply, Rod.

I've just come back from an unsuccessful dark site visit (weather, technical issues, human issues *sigh*), so I'll have to set up again in the observatory and go through the alignment process. I'll have a better go at sorting it out this time.

If seeing is the issue (it has to be part of the problem), wouldn't that also affect the Dec graph too? As in I should see the Dec vary as much too and therefore be able to use this as a test?

And I'll try the changes you suggest. Any idea what a good min move value would be?
Reply With Quote
  #13  
Old 16-10-2015, 06:46 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Quote:
Originally Posted by bugeater View Post
I find getting the line nice and horizontal to be quite difficult too. It seems to change its trend periodically. Not sure if it is wind or something else.

But periodic error is a red herring - it can't be that as the line you are watching is the dec axis, not RA
The pics I attached previously were during the Drift Align tool runs. It specifically uses the "red" Dec line each time as line that you need to make as horizontal as possible (no matter whether you are adjusting altitude or azimuth). Of course, that just makes things more confusing.
Reply With Quote
  #14  
Old 16-10-2015, 09:30 PM
Rod771's Avatar
Rod771 (Rod)
Turn the lights off!

Rod771 is offline
 
Join Date: Aug 2012
Location: Parklea NSW
Posts: 1,207
Quote:
Originally Posted by lazjen View Post
Thanks for the reply, Rod.

If seeing is the issue (it has to be part of the problem), wouldn't that also affect the Dec graph too? As in I should see the Dec vary as much too and therefore be able to use this as a test?

And I'll try the changes you suggest. Any idea what a good min move value would be?
Yeah , good point. One thing you can do if your using the latest version of PHD2 (2.5.0) is, after calibration run the guiding assistant which is on the Tools tab. What it does is disables guiding in both axis and measures the data then makes suggestions base on how the star is moving when unguided. This will give you an idea of how good or bad the seeing actually is. It also shows how close your PA is and, what I have found just tonight is, it helps you set your balance in RA. My RA graph had never been as good as my Dec, similar to you screen shot. After watching the RA graph rise and keep rising while the guiding assistant was enabled, I figured my balance was too far off. I just stopped the guide assistant, adjusted the counter weight, restarted the assistant and the RA graph leveled.

So along with seeing, balance could be affecting your RA guiding as it was mine.

Hope this helps. I know how it feels, stick with it.
Reply With Quote
  #15  
Old 16-10-2015, 11:20 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Thanks Rod. What I like about PHD2 is the (in general) quick feedback it gives. I think I'm using 2.5.0, so I'll give the guide assistant a go as well.

Now I'm itching to get it all going again, but that's probably going to be Sunday night if I'm lucky. At least there's a few things to try.
Reply With Quote
  #16  
Old 17-10-2015, 07:47 PM
Camelopardalis's Avatar
Camelopardalis (Dunk)
Drifting from the pole

Camelopardalis is offline
 
Join Date: Feb 2013
Location: Brisbane
Posts: 4,626
This isn't a helpful comment particularly, but the drift alignment function gives me headaches

Before getting any imaging done last night I checked my drift by using the DARV function in APT and by taking unguided exposures which resulted in round stars. However, PHD drift alignment showed a downward graph for Dec and guide assistant claimed my alignment was 6 arc minutes from the pole...
Reply With Quote
  #17  
Old 17-10-2015, 11:20 PM
bugeater (Marty)
Registered User

bugeater is offline
 
Join Date: Feb 2015
Location: Mitcham, Vic
Posts: 313
Quote:
Originally Posted by lazjen View Post
The pics I attached previously were during the Drift Align tool runs. It specifically uses the "red" Dec line each time as line that you need to make as horizontal as possible (no matter whether you are adjusting altitude or azimuth). Of course, that just makes things more confusing.
It shouldn't be confusing. Dec drift is the indicator of not being perfectly polar aligned. Hence you adjust the appropriate axis to eliminate this drift. Which adjustment (alt or az) depends on which part of the sky you are pointing at. What makes it difficult is there seems to be other factors at play (but not PE )
Reply With Quote
  #18  
Old 17-10-2015, 11:35 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Actually, I think the comment is (partially) warranted Dunk. I ran out of time before I had to pack everything up for my trip, so I never got a chance to try verifying that the process worked correctly.

Before I started using PHD2's tool, I had used Astrotortilla to do my previous alignments. While it worked ok, I wasn't completely happy with the results and the variability with repeat runs. So, on to PHD2.

I hope to have everything set up again tomorrow, so I'll repeat the PHD2 process again from scratch and report results, etc (assuming I sort out my other issues). I'll use the guide assistant tool Rod mentioned to help verify the results.
Reply With Quote
  #19  
Old 17-10-2015, 11:41 PM
lazjen's Avatar
lazjen (Chris)
PI cult member

lazjen is offline
 
Join Date: Dec 2012
Location: Flaxton, Qld
Posts: 1,668
Quote:
Originally Posted by bugeater View Post
It shouldn't be confusing. Dec drift is the indicator of not being perfectly polar aligned. Hence you adjust the appropriate axis to eliminate this drift. Which adjustment (alt or az) depends on which part of the sky you are pointing at. What makes it difficult is there seems to be other factors at play (but not PE )
PE can still be part of the problem, just like the seeing will be. It's just that I think we can rule out both as being the major component of the RA problem.

With my next set up I'll be able to leave it in place for a long time, so I'll be able to work through the issue(s) in less of a rush.
Reply With Quote
  #20  
Old 17-10-2015, 11:43 PM
Slawomir's Avatar
Slawomir (Suavi)
Amateur Photon Collector

Slawomir is offline
 
Join Date: Sep 2014
Location: Proserpine
Posts: 2,938
There could also be focuser/telescope flexing at various angles.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:24 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
OzScopes Authorised Dealer
Advertisement
NexDome Observatories
Advertisement
Bintel
Advertisement
Celestron Australia
Advertisement
SkyWatcher Australia
Advertisement
Meade Australia
Advertisement
Lunatico Astronomical
Advertisement
Astronomy and Electronics Centre
Advertisement