PHD2 guiding log - interpreting and improving?

[Stub Mandrel]

12 hours ago, vlaiv said:

PA is not critical thing for guiding really. Often I hear people say - you need perfect PA. This is true of unguided long exposure imaging - for guided it is not important.

If it is too far out it leads to RA and DEC being slightly out of true, so corrections to errors require a movement in both axes. I've noticed this as the RA and DEC traces appearing to 'shadow' each other, especially when wind or poor balance is causing larger errors.

[vlaiv]

3 minutes ago, Stub Mandrel said:

If it is too far out it leads to RA and DEC being slightly out of true, so corrections to errors require a movement in both axes. I've noticed this as the RA and DEC traces appearing to 'shadow' each other, especially when wind or poor balance is causing larger errors.

You are right - it should cause drift in both RA and DEC, but I think RA component will be many times smaller than DEC.

This image shows it nicely:

When we offset NCP we are getting two circles that overlap at two points (not necessarily E/W - it can be any two points, but opposite side of circle - it will depend on direction of PA). DEC rate is related to change in distance between two circles as you move along the circle. RA error is related to change in position of projection of current position from one circle to other. For small angle DEC drift will be much larger than RA - probably some trigonometric relation like sine of small angle is small while cosine being close to 1 kind of thing.

[Stub Mandrel]

4 hours ago, vlaiv said:

You are right - it should cause drift in both RA and DEC, but I think RA component will be many times smaller than DEC

Probably exaggerated by a poor setup. This is from when I was learning using the 130P-DS so guiding was atrocious, but you can see the peaks in RA are also dips in DEC. Looking at better sessions, the relationship is not obvious.

[vlaiv]

45 minutes ago, Stub Mandrel said:

Probably exaggerated by a poor setup. This is from when I was learning using the 130P-DS so guiding was atrocious, but you can see the peaks in RA are also dips in DEC. Looking at better sessions, the relationship is not obvious.

There are two more things that can happen so that error graph looks in sync (apart from vibration issue).

First is of course wind - wind will act on OTA from the direction it's blowing from, and if OTA happens to be at particular angle - this can cause problems with RA, DEC or combined (most of the time) - this will cause "sync" between errors.

Similar thing can happen with seeing caused by local thermals - here I think ground level seeing close to observing site - couple of hundred of meters - not tube currents nor high altitude seeing (like jetstream). Thermals are always in upward direction and cause larger disturbance in position in vertical direction - as observed by human from observing site - "skyward". OTA on EQ can be oriented with respect to this direction so it affects only RA (East / West facing), only DEC (South/North facing), or combination of the two - anything in between really - this will also cause "sync" in graph.

[tooth_dr]

My PA is close so I've sort of eliminated this!

Bruce and Ken on the PHD forum gave me some advice so if it's clear enough tonight I'll try it out.

I'll report back with the advice and the results if it's clear.  They have then said they will look at my graph and see if anything can be done to improve it via software.  Otherwise I'll wait until the summer and do the belt mod (or buy a Mesu).

[Jkulin]

With my Fracs Adam I use an ST80, it works fine and I do get excellent guiding.

@ollypenrice suggested sometime ago as did Vlaiv to extend your guide durations to 4 secs, I run with 5 secs and noticed an immense difference as I was no longer chasing the seeing.

For your Newtonian forget using a guide scope, use an OAG, far more accurate and it will make the balance far easier, I used to use an ST80 with my smaller 8" RC and I noticed a tremendous difference when I switched over to an OAG.

If you do switch then don't panic about the shape of your guide stars in phd, I chose the Celestron OAG on good advice from my mate as it really is a solid piece of kit.

[tooth_dr]

On 18/02/2019 at 10:01, Jkulin said:

With my Fracs Adam I use an ST80, it works fine and I do get excellent guiding.

@ollypenrice suggested sometime ago as did Vlaiv to extend your guide durations to 4 secs, I run with 5 secs and noticed an immense difference as I was no longer chasing the seeing.

For your Newtonian forget using a guide scope, use an OAG, far more accurate and it will make the balance far easier, I used to use an ST80 with my smaller 8" RC and I noticed a tremendous difference when I switched over to an OAG.

If you do switch then don't panic about the shape of your guide stars in phd, I chose the Celestron OAG on good advice from my mate as it really is a solid piece of kit.

Thanks John.  I have an ST80 that I could use, would mean a bit of rejigging things.  I briefly tried an OAG before with my newtonian with my DSLR, but sold it when I changed to CCD as it was only Canon.  I'll need to measure up my spacing to see if it's possible with my kit.

[Jkulin]

Yes Adam with a frac the back focus can be a problem, but with your Newtonian it should be fine.

As for the ST80 I have found it to be perfect for a guide scope.

[tooth_dr]

Hi guys. Here is my log from last night

The last run is the longest.

https://openphdguiding.org/logs/dl/PHD2_logs_X5Yl.zip

Dec is ok, RA I can’t seem to get smooth  any ideas?

 

Thanks

Adam  

 

[Stub Mandrel]

1 hour ago, tooth_dr said:

Dec is ok, RA I can’t seem to get smooth  any ideas?

Aggression is too high and it's overshooting?

Plus the backlash compensation seems too high.

[tooth_dr]

4 hours ago, Stub Mandrel said:

Aggression is too high and it's overshooting?

Plus the backlash compensation seems too high.

Thanks for replying!

Those are the default settings, and other settings were adjusted as a result of a 20 minute run of the guiding assistant!

Does the backlash affect RA or just DEC?

[Stub Mandrel]

40 minutes ago, tooth_dr said:

Thanks for replying!

Those are the default settings, and other settings were adjusted as a result of a 20 minute run of the guiding assistant!

Does the backlash affect RA or just DEC?

Hmm.. it's definitly over -correcting. BUT it seems to 'slip back' almost straight away. I wonder if the RA axis is too tight?

[michael8554]

The Guide Assistant will supply MinMove settings based on the "seeing" during the 20 minute run.

Once you apply those and get Guiding, you set Aggro and Hyst to give smooth guiding.

5 hours ago, Stub Mandrel said:

I wonder if the RA axis is too tight?

Go for the easy solution, RA is yoyo-ing, so reduce the Aggression !!

Michael

[tooth_dr]

Thanks Michael. Next night it’s clear I’ll try  that. I did change a few things but the immediate response to my graph was worsening so I reverted back. 

[tooth_dr]

Here are my logs from last night, if anyone can have a look.  I tightened the bracket holding the finder scope in place.  There was just a little movement when I pressed it, but this is now gone.   I also turned off dithering.

 

PHD2_DebugLog_2019-02-25_210248.txt

PHD2_GuideLog_2019-02-25_210248.txt

[tooth_dr]

Screen shots of runs last night, short and then longer run.  What can be deduced from this?

 

Thanks!

 

[michael8554]

I can't look at the logs on my tablet, and the horizontal scale on your second grab is too small to see whats happening from second to second - can you post a grab with the horiz + button hit enough to give a minute of the worst section?

Were the min moves as requested by the GA ?

Michael 

[tooth_dr]

41 minutes ago, michael8554 said:

I can't look at the logs on my tablet, and the horizontal scale on your second grab is too small to see whats happening from second to second - can you post a grab with the horiz + button hit enough to give a minute of the worst section?

Were the min moves as requested by the GA ?

Michael 

 

Thanks Michael, yes i ran GA twice over the course of the evening, and the same values were given both times.  Does that indicate poor seeing?

 

Here is a close up.  I dont seem to correct in DEC very much, and RA if always correcting the same way

 

 

 

[michael8554]

PA looks good, and RA is being corrected with a little overshoot.

Do you have to adjust the tracking rate after the belt mod ?

Minimum Dec drift and steady RA drift in one direction suggests incorrect tracking rate.

PE would drift in one direction  but come back to zero and maybe drift in the other direction after a worm period.

Might be worth doing Guide Assistant for 10 mins or so and watch what the unguided RA does over that period.

Michael 

[michael8554]

I've looked at your logs with Log Viewer.

The GA session Log 2 at 21:13 shows your RA drift quite clearly.

It starts heading off at 21:18 and levels off just as you stopped.

If you had run another 6 mins or so you could see if it climbs back, which would be PE, or if it continued dropping, which would be Tracking Rate.

The rest of the logs show a lot or RA yoyo-ing, you could try running less aggression as an experiment, after you've sorted the PE or Tracking Rate.

But I'm getting out of my depth on these results, so try sending your logs to the google "Open PHD2 Guiding" Forum, the guys who developed PHD2 run it, so they will set you straight.

How to send the logs is in help menu-> upload log files

Michael

[tooth_dr]

1 hour ago, michael8554 said:

I've looked at your logs with Log Viewer.

The GA session Log 2 at 21:13 shows your RA drift quite clearly.

It starts heading off at 21:18 and levels off just as you stopped.

If you had run another 6 mins or so you could see if it climbs back, which would be PE, or if it continued dropping, which would be Tracking Rate.

The rest of the logs show a lot or RA yoyo-ing, you could try running less aggression as an experiment, after you've sorted the PE or Tracking Rate.

But I'm getting out of my depth on these results, so try sending your logs to the google "Open PHD2 Guiding" Forum, the guys who developed PHD2 run it, so they will set you straight.

How to send the logs is in help menu-> upload log files

Michael

It continues dropping see below:

 

 

 

[tooth_dr]

Thanks Michael. I really appreciate all your help on this. 

[michael8554]

9 hours ago, tooth_dr said:

It continues dropping see below

Oh dear, I really hope for you that I'm not misinterpreting this as wrong Tracking Rate.

I could hazzard a guess that the ripple on the straight dip is the PE.

Is Tracking Rate a setting in EQMOD if you're using that?

Or have they given you the wrong ratio pulleys?

Best get those logs over to Open PHD Guiding.

Michael 

[tooth_dr]

1 hour ago, michael8554 said:

Oh dear, I really hope for you that I'm not misinterpreting this as wrong Tracking Rate.

I could hazzard a guess that the ripple on the straight dip is the PE.

Is Tracking Rate a setting in EQMOD if you're using that?

Or have they given you the wrong ratio pulleys?

Best get those logs over to Open PHD Guiding.

Michael 

Thanks Michael

I dont have the belt mod done, my mount is a stock EQ6-pro (white model 2009), but it's been 'serviced' a couple of times, including new SKF bearings and grease.

The tracking rate is set in EQMOD, I cant remember what it's at maybe 0.5x.  Does it need to go up or down do you think?

I've posted these on the PHD forum, and Bruce has replied suggesting that the RA issue is maybe due to sagging in the guiding setup (something physically pulling or hanging down), not due to rate.  I feel my guidecam and rig is pretty solid with no loose or hanging wires, everything is clipped in placed, and I only have 2 wires coming down from the scopes - 12v and 1xUSB.

[michael8554]

So not really a solution, but good news, not Tracking Rate.

Tracking Rate is the unguided RA rate, usually Sidereal.

Guiding Rate is a fraction of Tracking Rate that PHD2 applies to the Tracking Rate to guide, plus to move west, minus to move east.

0.5x is good, you can try up to say 0.9x to chase backlash if you had it.

Belt mod was someone else on sgl.

Can't see your post on Open Phd so can only say that sub-pixel guiding involves micrometre moves, so a hairs breadth sag in your guidescope setup will show on your guiding

Michael