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Astrophotography and Sketching >> Beginning and Intermediate Imaging

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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
PHD driving me mad....Help new
      #5461113 - 10/08/12 07:02 PM

Hi All

I have been getting slightly egg shaped stars on 5 minute exposures so looked at the graph in PHD and it wasn't too good ...lots of peaks above and below the centreline.

I found a good guide called 'A Guide to PHD Guiding by Greg Marshall' and had a really good read of it ..however no matter what settings in 'the brain' of PHD I tried I couldn't get the red alt line to stay near centre.

SO tonight I did the full polar alignment routine with PHD ...even though I thought I was pretty well polar aligned by the drift method done a long time ago.

So I did the whole routine and got the red dy line with alt guiding off to stay really steady at the center ..did everything by the book and adjusted all the right knobs with the scope in all the right positions.

So it is now 100% perfectly polar aligned.

But still when guiding the red alt line doesn't stay central but drifts slowly down ...it doesn't matter whether alt guiding is set to auto, north or south (I realise that now its perfectly polar aligned I shouldn't need alt guiding at all but surely with it on I shouldn't get downward movement )

i have tried messing with loads of setting on the fly but cant seem to get anything smooth.

I don't seem to remember having this problem years ago when I first started using PHD so am wondering about downloading an earlier version of it.

Am begining to tear my hair out ...been 4 hours tonight and got nowhere

Any ideas?

Tom


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Mike Wiles
scholastic sledgehammer


Reged: 02/04/09

Loc: Goodyear, AZ
Re: PHD driving me mad....Help new [Re: pubquiz]
      #5461162 - 10/08/12 07:41 PM

Have you seen this article by PHD author Craig Stark? Seriously, I don't even use PHD and I found a column he wrote here on Cloudy Nights a few months ago remarkably informative. Check it out: What to do When PHD Guiding isn't Push Here Dummy

Mike


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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: PHD driving me mad....Help new [Re: Mike Wiles]
      #5461178 - 10/08/12 07:52 PM

Thanks for that Mike ....that looks a great article and one that didn't come up in my searches for an answer.

Will give it a good read tomorrow.....off to bed now...1 AM here in UK.

Tom


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michael hester
professor emeritus


Reged: 11/28/08

Re: PHD driving me mad....Help new [Re: pubquiz]
      #5461978 - 10/09/12 12:00 PM

The red alt line is saying that your polar alignment isn't 100%. Otherwise the line should go nowhere. Some other considerations:

- Seeing will affect your guiding. If the seeing is really bad expect the PHD graph to jump around.
- You can change the maximum guide distance in the phd graph or on the brain menu. If you're jumping around too much try reducing the Max Dec to minimize the jumping.


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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: PHD driving me mad....Help new [Re: michael hester]
      #5462036 - 10/09/12 12:30 PM

Hi Michael

the red line slowly dropping is while I am guiding in alt and az with alt guiding set ON at auto north or south....so even with a polar alignment slightly off it should still send guiding corrections to alt as well as az.

When doing the polar alignment I did all the instructions found on various sites ...ie point the scope at a star near the meridian/equator and calibrate then change PHD's graph to dx/dy and turn alt guiding off.

Then use the Az adjustment on the mount till the red line remains flat level and constant ...this I did till it was spot on...really flat and not deviating.

Then point scope at a star low down to the East or West (I used East) and re calibrate PHD then again change graph to dx/dy and turn off alt guiding...then use the Alt adjustment on mount to get a flat red line...again I got this absolutely spot on so I assume scope is now perfectly polar aligined.

I did only do this once though so maybe I should have repeated the procedure a few times?

Will give it all another go next clear night (whenever that will be!)

Was curious why the red line seemed to drift down though even when guiding was turned ON...surely it should correct for any drift either way.

Tom


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Mike7Mak
Pooh-Bah
*****

Reged: 12/07/11

Loc: New York
Re: PHD driving me mad....Help new [Re: pubquiz]
      #5462121 - 10/09/12 01:28 PM

Quote:

I did only do this once though so maybe I should have repeated the procedure a few times?

Was curious why the red line seemed to drift down though even when guiding was turned ON...surely it should correct for any drift either way.




Yes, it's an iterative process. Unless the mount base is absolutely, perfectly level the adjustments interact and the drift needs to be done a few times. Also you don't really need to recalibrate going from meridian to the horizon for the purpose of drift aligning.

If both graph lines are oscillating due to seeing try increasing 'min motion' and/or exposure length.

If it can't keep up with dec drift you may have a lot of backlash and/or an out of balance dec axis. Try increasing the dec 'max' till it starts moving. But if there's a lot of backlash you may end up with extremne dec oscillations. The quick fix for that is to guide in one dec direction only.


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michael hester
professor emeritus


Reged: 11/28/08

Re: PHD driving me mad....Help new [Re: Mike7Mak]
      #5462468 - 10/09/12 04:37 PM

I was pointing out that the red line shouldn't drift anywhere if the polar alignment was spot on, but there is something that bugs me here. You mention azimuth and altitude rather than right ascension and declination.
I would assume that your pier is equatorial but is this the actual case?

Also backlash could be a reason why the mount isn't responding to guide commands. Does the mount start responding to commands after a while?

How long is it taking to calibrate each axis?
- This question is because of how PHD determines the axes of each direction. If it takes too long to calibrate then it may confuse periodic error in Right Ascension as being the declination movement. If your PE is high it may even accept a full calibration of the DEC axis based on your PE. I run PHD at the highest possible calibration step that it can still detect the guide star after because of this.

Edit: question summary

What is your mount and how is PHD talking to it?

How long is it taking to calibrate each axis? How long does it take to clear the dec backlash when calibrating?


Edited by michael hester (10/09/12 04:43 PM)


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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: PHD driving me mad....Help new [Re: michael hester]
      #5462734 - 10/09/12 07:38 PM

Hi Mike and Michael

Thanks for the replies

Will try what you suggest Mike

Michael: Yes maybe I worded it wrong but if you look at my sig below my postings you will see that my mount is equatorial...a Losmandy G11...the calibration takes place pretty quick ...I have tried various settings and it only usually takes about 12 'movements'...backlash is also cleared pretty quickly but I havn't timed it .....not been aware of any exessive backlash when using the mounts hand controller.

Thanks again for relies and help ...will stick at it and keep posted to this thread

Tom


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D_talley
Carpal Tunnel
*****

Reged: 07/07/05

Loc: Richmond VA
Re: PHD driving me mad....Help new [Re: pubquiz]
      #5464953 - 10/11/12 07:53 AM

Quote:

Hi All
..however no matter what settings in 'the brain' of PHD I tried I couldn't get the red alt line to stay near centre.

SO tonight I did the full polar alignment routine with PHD ...even though I thought I was pretty well polar aligned by the drift method done a long time ago.

So I did the whole routine and got the red dy line with alt guiding off to stay really steady at the center ..did everything by the book and adjusted all the right knobs with the scope in all the right positions.

So it is now 100% perfectly polar aligned.

But still when guiding the red alt line doesn't stay central but drifts slowly down ...it doesn't matter whether alt guiding is set to auto, north or south (I realise that now its perfectly polar aligned I shouldn't need alt guiding at all but surely with it on I shouldn't get downward movement )

i have tried messing with loads of setting on the fly but cant seem to get anything smooth.

I don't seem to remember having this problem years ago when I first started using PHD so am wondering about downloading an earlier version of it.

Am begining to tear my hair out ...been 4 hours tonight and got nowhere

Any ideas?

Tom




Tom, I have had the same problem you have had for the past two times I have gone out. My mount and scope have worked fine for years. I use PHD with a QHY5 guide scope. I have never needed to get perfectly polar aligned using the guider with PHD.

Last month I could not get any tracking more than a minute with my mount. I would calibrate and then start guiding. A minute or so later I get the warning sound that the guide star was lost. I would go back and calibrate and the guide star is lost shortly after I start to guide. I fought this for several hours. Gave up and went home. I though that there was a problem with the autoguider cable and I made three more just to make sure they worked.

The last time I went out I drift aligned my mount so that there would be no star movement for several minutes. I also made sure the scope was balanced with a bias to the East. Connected the guide camera with the new cable and started PHD. I watched the graph and could see a stair step plot of the DEC as it ran off of the screen. *BLEEP*! I could not get a smooth run the entire night with PHD and the polar aligned mount. What was causing the stair step graph of the DEC plot? It would happen each time I started to guide.

I then connected my SBIG STV and it guided better but still not as perfect as it has before. I still had oval star with a 1200mm scope at F/4. I have shot pin point stars at 3550mm F/10 with this setup.

My next plan is to install a pier at home so that I can eliminate any polar align issues and test this mount, the Gemini controller, and any flexure in the optics that I may have missed. It is just hard having the time and clear nights to see what is causing the problem. It could be a problem with the clutch pads not holding or the autoguider port in the Gemini not working correctly. I have another Gemini I will swap out and test.

Good luck and I will report what I find.


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pfile
Post Laureate


Reged: 06/14/09

Re: PHD driving me mad....Help new [Re: D_talley]
      #5465395 - 10/11/12 01:33 PM

how many calibration steps did PhD make? i find that with my G11/G2 if the # of steps is too small (~7-10) then the calibration is not accurate.

also i have read here and there that the G2 might ignore small corrections. the other night i noticed that i had to have my calibration step set to at least 350ms (using an OAG, so need small steps) or the declination would not move.

if you use a separate guidescope you may not see this problem during calibration, but if your max dec pulse is set to a smallish number, the G11 may never see the dec corrections...


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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: PHD driving me mad....Help new [Re: pfile]
      #5465547 - 10/11/12 03:38 PM

Thanks for the replies

Dwight: Yes I also use a Losmandy G11 and a QHY5 as the guide cam, and it seems to be a problem that has just manifested itself.

The guide scope is a WO Megrez 72 and it's all on a concrete pier in an observatory....am going to do a few more iterations of the polar aligning when conditions allow but like I say it should still correct in dec even when not spot on...it did before.

Will be interested to hear your results.

pfile: interesting ...I think it took about 8 calibration steps so will try different settings to make it do more and also experiment with the max dec duration (ms) setting as well.

Hopefully will get a clear night this weekend.

Tom


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D_talley
Carpal Tunnel
*****

Reged: 07/07/05

Loc: Richmond VA
Re: PHD driving me mad....Help new [Re: pubquiz]
      #5466100 - 10/11/12 10:46 PM

Here is a quick result from my testing. My settings in the hand controller for guide speed had shifted to .2 When I set it back to .5 everything started working again and I can guide. I am at this moment taking some long shots. So far pin point.

Take a look at yours.


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Ugmul
super member


Reged: 05/17/11

Loc: Tucson AZ
Re: PHD driving me mad....Help new [Re: D_talley]
      #5466236 - 10/12/12 01:17 AM

Glad you got it to work, for my scope I normal set the guide speed to 1.0, I found at .5 sometimes can't keep up and then the graph just gets worse. With the 1 setting and PhD doing a sub every 1 to 2 seconds, both graphs stay very very close .

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D_talley
Carpal Tunnel
*****

Reged: 07/07/05

Loc: Richmond VA
Re: PHD driving me mad....Help new [Re: Ugmul]
      #5466662 - 10/12/12 10:48 AM Attachment (35 downloads)

Here was my track before I fixed the guide speed.

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michael hester
professor emeritus


Reged: 11/28/08

Re: PHD driving me mad....Help new [Re: D_talley]
      #5466912 - 10/12/12 01:49 PM

That graph almost makes me cringe. Although yes I drift align now but you shouldn't have a dec line getting away from you that fast if your polar alignment is good. The star drifted 4 pixels over a 50 second window.

What i don't get about that graph is the jump in the middle. Was that the mount responding to the guide command?

Also, off axis guider or guide scope? I can see that this would be fine in an OAG. In a guide scope of 1000mm f/l or less that drift limits you to a 5 minute exposure or less.


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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: PHD driving me mad....Help new [Re: michael hester]
      #5466927 - 10/12/12 02:49 PM

I don't have Gemini on my Losmandy (It's 'push to' with an Argo Navis) the available guide speeds are .3, .5, then 2 4 8 and 16x on the 'Losmandy Digital Drive System' box (no seting of '1' is available...I have always used .5....also tried .3 but .5 always seemed best.

Am in the observatory as I type this waiting for the clouds to clear

Tom


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pfile
Post Laureate


Reged: 06/14/09

Re: PHD driving me mad....Help [Re: pubquiz]
      #5467122 - 10/12/12 05:20 PM

that's interesting about the guide speed. mine is set to 0.5 which i think is the default for the gemini-2. it may make sense to use 1x sidereal for guiding, as craig himself points out in the "when phd is not push-here dummy" article he wrote recently.

of course then the # calibration steps will go down and if it's true that the G2 is "swallowing" short guide pulses, that would make the problem worse. at 1x guide rate the pulses would need to be shorter...


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Gregk
Carpal Tunnel
*****

Reged: 11/19/06

Loc: San Tan Valley, Az,
Re: PHD driving me mad....Help new [Re: pubquiz]
      #5467281 - 10/12/12 07:13 PM

Did U turn dec guiding back on after the polar alignment?
Is resist switching on?
recalibrate after?
restart phd?
dec balance?
Can U tell us more about your setup load and settings U are using in PHD

Edited by Gregk (10/12/12 07:16 PM)


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D_talley
Carpal Tunnel
*****

Reged: 07/07/05

Loc: Richmond VA
Re: PHD driving me mad....Help new [Re: michael hester]
      #5467305 - 10/12/12 07:25 PM

Quote:

That graph almost makes me cringe. Although yes I drift align now but you shouldn't have a dec line getting away from you that fast if your polar alignment is good. The star drifted 4 pixels over a 50 second window.

What i don't get about that graph is the jump in the middle. Was that the mount responding to the guide command?

Also, off axis guider or guide scope? I can see that this would be fine in an OAG. In a guide scope of 1000mm f/l or less that drift limits you to a 5 minute exposure or less.




Yes that graph is painful when you are out and trying everything to fix it.
I also could not figure out why the DEC is moving so much since I was polar aligned. Could be caused by poor adjustment commands in PHD that was trying to keep up with the star.
The bump in the middle is where I started it back up again after finding the lost star.
Guide camera is on a scope attached to the imaging scope. Now everything works as it should by changing the guide speed back up to .5 from the bad setting of .2


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pubquiz
scholastic sledgehammer


Reged: 10/07/04

Loc: Lancashire England
Re: PHD driving me mad....Help new [Re: D_talley]
      #5467339 - 10/12/12 08:06 PM

pfile: there is no 1x setting just .3 then .5 then 2x and so on as above which is curious as I suppose it must guide at 1x but there is definately no 1x shown on the settings box

Greg:1)Yes I turned dec guiding back on

2)resist switching is on (have never tried the lowpass filter setting)

3) I didn't recalibrate after as I was on the same star and hadn't moved to a new sky area.

4) just carried on in PHD not5 sure what you mean by re start ...just kept it running but clicked on a off the guide star and started afresh a few times without rebooting PHD.

5) it is balanced well in dec and and RA ...if any bias it is a very little keeping load on the gears.

6) the load is at the top of the G11's limit...I have weighed it and it is just within the limits of the mount...the settings have varied alot as I have tried various ones but as I remember the defaults seemed fine a while ago.

I only got about 10 mins tonight before I gave up with the cloud but dec tracking did seem to be a bit better....hard to be conclusive though as it went total cloud so gave up and came in...off to bed now will try again tomorrow weather permiting.

Much appreciate all the replies and help.....won't let it beat me

Tom


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