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Andyb90

PHD2 Guiding - Very Spikey Graph - Help!

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Hi Everyone,

I setup PHD2 last night to do some test guiding, but I'm getting a very spikey graph. Here is a screenshot of the graph:

56c7624d4eb97_Capturegraph.thumb.JPG.275

I'm using my QHY5ii camera attached to a Skywatcher 9 x 50 finder scope. I have it secured in some baader guide scope rings, which are bolted directly onto a dovetail bar.
The dovetail bar is bolted directly to the top of the tube rings that my 80 ED scope sits in. So I think the setup is pretty solid.

In PHD I'm using the on-camera setting with an ST4 cable between the QHY5 and mount.

Also I've balanced the setup east heavy in RA on my HEQ5.

Edit: Just to add I polar aligned the mount using the polar scope.

I ran the guiding assistant too and here is the screenshot. I applied the recommended changes to the RA and DEC min move.

Capture.JPG.2022c47346bdac871df8c2e0881c

I kept the exposure setting to 3 seconds, but it didn't seem to help. I also reduced the DEC agression to 70, but that didn't seem to help either.

I'd really appreciate any help on this problem, as I'm not sure what to do to smooth the graph out.

To be honest I didn't attempt any subs as the graph looked so bad I thought I'd got no chance of a decent result.

Andy.

Edited by Andyb90
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Only needs to be slightly out of balance, did you try the polar alignment tool , turn on the corrections in the graph so you can see when they're being sent and what effect they have.

Dave

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A little out of balance won't help and the PA needs to be very very good, if you have the habdset run the built in PA routine a couple of time, use different stars each time. I haven't tried it but there is a drift align routine in PHD if you have no handset.

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PHD guiding assistant always seems to recommend 0.10 for MinMo.  I wonder if this leads to excessive 'chasing'.  You might do better with 0.24 or higher.   

But this does look a bit off.  Espec that red line.  Are you certain you don't have a cable dragging somethings somewhere?

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I am no expert but the scariest number in your screengrab for me is 20.1 pxl of declination backlash.

I recently changed all the bearings in my HEQ5 for FAG/SKF and spent several hours tuning out the backlash following Astrobaby's guide and eventually got the graph flat with minimal guide pulses required.

Do a Google search for Astrobaby HEQ5 strip down - I feel sure some time following the part of the document about getting rid of backlash will pay handsome dividends.

 

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I had the scope pointing near Merak in Ursa Major whilst doing the testing, so North East. I'd got RA weighted quiet heavy on the counter weight side. I'm wondering if that was wrong and it should have been weighted slightly towards the scope side.

Also DEC was camera heavy and again I'm wondering if that was correct for the position the scope was in.

For drift alignment I normally use the DARV function in the APT tool, but was trying to save some time last night by polar aligning with just the polar scope :-( Will drift align next time.

I should have had the corrections box checked, will ensure that is done next time.

I think my cables are pretty secure, although I use elastic around the dovetail bar and tripod legs to keep them in place. I'm wondering if velcro ties would be better.

Skipper Billy - I saw your graph and was very impressed. I've been thinking about tuning of the mount and possibly the belt mod. Will have a look at the Astrobaby site.

Andy.

 

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I cant prove that the belt mod made much difference to the tracking - but I know for SURE that it made it almost silent !  

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I always recommend to post the PHD log file as it shows a lot more than screen shots. The screen shot can be deceptive as the spikiness depends on the scales used on the x and y axes. And I can't see the guide pulses on the screen shot.

If you are testing guiding you should aim near the celestial equator. Otherwise you'll have small RA movements which could mask other problems. 

Also, you are using ST4 guiding but I can't tell if PHD is also communicating with your mount to get the Declination. If not and if you haven't entered it manually, then your RA corrections will be off.

How good is your calibration? The target chart looks a bit skewed NE-SW which would warrant a check of the calibration.

 

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I found the guide log and attached it.

Guide Log.txt

Will aim towards celestial equator next time I test.

I've got EQASCOM setup and an EQDIRECT cable for controlling the mount, but I had nothing selected for Aux Mount. Will select the 'EQMOD ASCOM HEQ5/6' option.

Is there an option in PHD for checking calibration?

Andy.

 

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The first part of the log is missing so it wont load into PHD Log Viewer. Make sure you load up the entire log for the session.

Calibration is the first thing PHD does when you first start guiding. Most likely it has saved your calibration in your profile and is reusing it. But if you've changed you guiding setup since then it would be incorrect.

You can view your calibration under Tools > Review Calibration and force a new calibration with Tools > Modify Calibration>Clear Calibration Data followed by starting guiding.

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Try these settings (what I use)

Mx RA: 1000, Min mo: 0.04

Mx DEC: 300, Min mo 0.04

Exposure time: 3 - 4s (depending on conditions)

Leave it on "Auto" if you dont know which way your mount likes to drift.

Thats what I use to guide an NEQ6 mount (9x50 attached in the same way as yours), it should be roughly the same for an HEQ5. The min mo should be quite low, as you are using quite a short focal length lens to guide through. The exposure length is what averages out variable conditions (not the min mo). Also, the Hys function is also what smooths out the correction, so increase that a bit too.

post-5513-0-71898900-1451848616.jpg

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Scary graph.....try to get to phd2 website, there is a help forum and they are very good, Bruce and Andy will guide you..pun unintended.

your Dec backlash is large as pointed out, you can lower your mx Dec motion so that it does not make really dramatic swings.

your pa is reported as 0.3 arc mins which on the face of it sounds o.k but.....you have only run the assistant for just over a min and that's not long enough for a reliable reading....

if im not mistaken you have been given good advise on polar alignment, just make sure that is right first.

ph settings are unlikely to be your issue, polar alignment, balance, cable drag......flexure..... you seem to have nailed.

then you can start to look at PhD.

have you done a good calibration at Dec zero? Post a screen shot of that.

Ray

Edited by libraryman

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I'll grab the full guide log off my laptop and upload.

Unfortunately I didn't notice the review calibration option before. I did a reset of the settings in PHD2 at the end of the session, which has cleared my calibration data. I'll grab a screenshot of the data next session.

Will also ensure I run the guiding assistant for longer and experiment with the min move, aggression and hysteresis settings. I did make changes during the session, but not in a very systematic way. So next session I'll be more systematic and ensure I only change one parameter at a time.

I've found the PHD forum google group and will see if I can join it.

Is it also worth doing the following ? :

  • Turning off guiding to see how the star moves without it.
  • Opening up the cover of the mount to have an initial look at the gears. Could I use the handset with the cover off to see how the gears are meshing?

Thanks for all the comments and suggestions so far. As always I really appreciate peoples responses.

Andy.

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If you turn off the guiding you will see the raw drift, seeing etc, just as the assistant does.

if you take off the covers, what can you achieve? I would guess not much.

first things first as suggested, joining the forum is easy, upload a guiding log to them, they are preferred to help them diagnose your problems.

 

Ray

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Any ideas on what's up with mine?

I have a feeling it's balance issues. As I can't balance the DEC propperly due to the short dovetail.

20160218_204923-1.jpg

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Looks like mine when it's not balanced, as when I swop the DSLR for the QSI and forget to rebalance it :rolleyes2:

Dave

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16 minutes ago, Daniel-K said:

Any ideas on what's up with mine?

I have a feeling it's balance issues. As I can't balance the DEC propperly due to the short dovetail.

Hi

Dunno what scope or mount you have but either a longer dovetail or balancing with a suitable counterweight should help :)

Louise

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3 hours ago, Daniel-K said:

Any ideas on what's up with mine?

I have a feeling it's balance issues. As I can't balance the DEC propperly due to the short dovetail.

 

A mis-balance shouldnt give you that sort of graph. It would be more likely for just the DEC to drift - rather than have both dancing about like that.

One thing I can suggest is once you have a decent graph, stay well away from the telescope as walking about can upset the guiding quite easiy - thats why I always tip-toe away once its running (or activate it from the house).

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1 minute ago, Uranium235 said:

A mis-balance shouldnt give you that sort of graph. It would be more likely for just the DEC to drift - rather than have both dancing about like that.

One thing I can suggest is once you have a decent graph, stay well away from the telescope as walking about can upset the guiding quite easiy - thats why I always tip-toe away once its running (or activate it from the house).

It's like this from the start it never settles down

 

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This is via ST4 "on camera" guiding yea? 9x50 finderguider?

Really, your RA line should be flat-ish (mine was, even on a CG5), it only ever jumped about when it was cloudy or windy. Its either mechanical (eg: something is loose/wobbly) or its in PHD2. I'd be half tempted to downgrade you to PHD1 just to cut out all the unnecessary gubbins that came with the new version - I'll bring it along to SGL XI if youre interested ;)

 

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12 minutes ago, Uranium235 said:

This is via ST4 "on camera" guiding yea? 9x50 finderguider?

Really, your RA line should be flat-ish (mine was, even on a CG5), it only ever jumped about when it was cloudy or windy. Its either mechanical (eg: something is loose/wobbly) or its in PHD2. I'd be half tempted to downgrade you to PHD1 just to cut out all the unnecessary gubbins that came with the new version - I'll bring it along to SGL XI if youre interested ;)

 

Yeah this st4 and a 9x50 I'm not overly keen on PHD2 to be honest. Any help would be be great

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No prob, I've just cobbled together the required files in anticipation. What camera is it? (QHY5?)

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Just got my full guide log off the laptop, here it is.

PHD2_GuideLog_2016-02-18_202410.txt

I posted a thread on the Open PHD google group too.

Also I've been reading the below article on guiding and it gives some info about DEC balancing

http://www.blackwaterskies.co.uk/2013/07/phd-guiding-basic-use-and.html

Quote

If you have southward drift:

- If the scope is pointing South of the zenith, imbalance the scope so that the North (lower) end is heavy.
- If pointing North of the Zenith, again imbalance so that the North (higher) end is heavy.

If your polar alignment is causing a gradual northward drift instead, then you reverse the imbalance:

- Pointing South of zenith, South/higher end heavy.
- Pointing North of zenith, South/lower end heavy.

Does this advice about dec balancing look correct?

Andy.

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5 hours ago, Andyb90 said:

I'll grab the full guide log off my laptop and upload.

Unfortunately I didn't notice the review calibration option before. I did a reset of the settings in PHD2 at the end of the session, which has cleared my calibration data. I'll grab a screenshot of the data next session.

Will also ensure I run the guiding assistant for longer and experiment with the min move, aggression and hysteresis settings. I did make changes during the session, but not in a very systematic way. So next session I'll be more systematic and ensure I only change one parameter at a time.

I've found the PHD forum google group and will see if I can join it.

Is it also worth doing the following ? :

  • Turning off guiding to see how the star moves without it.
  • Opening up the cover of the mount to have an initial look at the gears. Could I use the handset with the cover off to see how the gears are meshing?

Thanks for all the comments and suggestions so far. As always I really appreciate peoples responses.

Andy.

That's why I recommend to post the log file. It includes all the calibration data and even the calibration run if it was done in the same session. The only thing it doesn't show is the star profile so you can screen shot that or there is even an option in the menu for logging the star profiles as JPEGs. A screen shot for that is fine.

Personally, I wouldn't change anything, except maybe to reset to default values, until you know what is going on. There are so many variables you need to approach it methodically.

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