PHD2 guiding log - interpreting and improving?

[tooth_dr]

Hi everyone.

I've just recently started to look at the figures for my guiding.

I'm guiding with a finderscope with a ZWO ASI120MM camera.  I'm imaging with an ED80, with 0.85x FF so about 520mm focal length.  On an EQ6-pro mount (2009), mounted on a pier.

 

Is it as bad as it looks, and if so what can I do to improve?

Thanks

Adam

 

 

 

 

PHD2_GuideLog_2019-02-05_203734.txt

[vlaiv]

Well, I think it can be better, or to be more precise - two times better?

Your total RMS is 1.55" and that is quite high - you want that to be around 0.7", peaks also need to be less than what graph shows (over 3") - you don't want them to go over 1.5" - 2.0".

First step would be to fiddle a bit with your mount if you have not done that already - maybe re grease it, and adjust everything (play, backlash, gear meshing and such) - and see what improvement that gives you.

[LightBucket]

10 minutes ago, tooth_dr said:

Hi everyone.

I've just recently started to look at the figures for my guiding.

I'm guiding with a finderscope with a ZWO ASI120MM camera.  I'm imaging with an ED80, with 0.85x FF so about 520mm focal length.  On an EQ6-pro mount (2009), mounted on a pier.

 

Is it as bad as it looks, and if so what can I do to improve?

Thanks

Adam

 

 

 

 

PHD2_GuideLog_2019-02-05_203734.txt

But your images are superb and speak for themselves, so if it aint broke.....

I think sometimes in this hobby we look for issues that are not really issues, if you know what I mean...

[tooth_dr]

4 minutes ago, vlaiv said:

Well, I think it can be better, or to be more precise - two times better?

Your total RMS is 1.55" and that is quite high - you want that to be around 0.7", peaks also need to be less than what graph shows (over 3") - you don't want them to go over 1.5" - 2.0".

First step would be to fiddle a bit with your mount if you have not done that already - maybe re grease it, and adjust everything (play, backlash, gear meshing and such) - and see what improvement that gives you.

Thanks vlaiv. I did a strip down, changed a few bearings and greased it last year.  I thought it was rightly adjusted. I do have an issue with my Dec axis making balancing hard. If I was to take it apart again would I be better doing the belt mod?

[tooth_dr]

4 minutes ago, LightBucket said:

But your images are superb and speak for themselves, so if it aint broke.....

I think sometimes in this hobby we look for issues that are not really issues, if you know what I mean...

I agree! I’m thinking that if I switch to my 10” newt then this level of guiding may not be good enough?

[Adreneline]

Hi Adam,

I've battled with PHD2 since I started guiding two years ago. I've used the Guiding Assistant and found it gave worse results! After lots of trial and error and experimentation I now typically  achieve this with essentially the default values. I use a belt-modified NEQ6 and an ED80 with a SW Guide Scope and ASI 120MM.

I also set the ASCOM PulseGuide Setting in EQMOD to x0.50 on both RA and DEC rate. I don't know why I do it but it seems to work better!

I would reiterate the fact that your images are amazing irrespective of the Guide Plot. The trouble is you can be haunted by that nagging doubt "could they be better". A tough one!

HTH's

Adrian

[vlaiv]

11 minutes ago, tooth_dr said:

I agree! I’m thinking that if I switch to my 10” newt then this level of guiding may not be good enough?

Just go by rule of thumb - guide RMS should be about half of imaging resolution. EQ6 does have lower limit and that would be about 0.5-0.6" RMS. You can't expect lower figures than that on regular basis.

I think that belt mod is worth the money and time to do it. Your tracking / guiding will benefit from it for sure.

[Stub Mandrel]

There is also a very good PDF on the PHD2 site that gives a lot of useful advice.

It's also worth experimenting to see which algorithms work best with your kit.

[almcl]

For a detailed analysis of your guiding performance, it may be worth posting your guide and debug logs over on the PHD2 Google group (here). (Instructions  for posting logs here: https://openphdguiding.org/getting-help/)

Bruce and Andy are usually pretty responsive to requests for help and can point to where problems, if any, may lie and how to address them.  

[david_taurus83]

Hi Adam,

 

I would say the belt modification would make a world of difference. Maybe a longer focal length guide scope? I use a 60/280mm guide scope, setup and strip down each time and polar align with Sharpcap. I never drift align, I regularly see my graphs below 0.7 arc second. Very rare it goes above 1". With a belt mod and some fine tuning to your PA i reckon you could halve that result you have there each night.

[spillage]

I would recommend running the guiding assistant and checking you PA. Also do you only guide one way in Dec. I normally turn off Dec guiding and if there is a drift north or south I just turn that on as needed. The belt mod will make a big difference and well worth the price. I know they are not cheap but I have found since using the polemaster has really improved my tracking.

[tooth_dr]

2 hours ago, Adreneline said:

Hi Adam,

I've battled with PHD2 since I started guiding two years ago. I've used the Guiding Assistant and found it gave worse results! After lots of trial and error and experimentation I now typically  achieve this with essentially the default values. I use a belt-modified NEQ6 and an ED80 with a SW Guide Scope and ASI 120MM.

I also set the ASCOM PulseGuide Setting in EQMOD to x0.50 on both RA and DEC rate. I don't know why I do it but it seems to work better!

I would reiterate the fact that your images are amazing irrespective of the Guide Plot. The trouble is you can be haunted by that nagging doubt "could they be better". A tough one!

HTH's

Adrian

Thanks Adrian. I’ve been playing with the eqmod rates too and around 50% seems ok for me too. We are using the same kit pretty much apart from the belt mod.

How is your guidescope mounted? 

[tooth_dr]

3 hours ago, vlaiv said:

Just go by rule of thumb - guide RMS should be about half of imaging resolution. EQ6 does have lower limit and that would be about 0.5-0.6" RMS. You can't expect lower figures than that on regular basis.

I think that belt mod is worth the money and time to do it. Your tracking / guiding will benefit from it for sure.

I think I might do the mod, but want to see if there is a simpler way to improve.

My current imaging resolution is 2.18”/pixel.  When I swop to my bigger scope it will be 0.93”/pixel.

 

[tooth_dr]

3 hours ago, Stub Mandrel said:

There is also a very good PDF on the PHD2 site that gives a lot of useful advice.

It's also worth experimenting to see which algorithms work best with your kit.

Thanks ? I’ve seen the different algorithms but haven’t tried them out. 

[LightBucket]

I have to be honest, until the last few weeks I have always used PhD version 1 as it’s simple with no bells and whistles and it just works.....

[tooth_dr]

4 minutes ago, LightBucket said:

I have to be honest, until the last few weeks I have always used PhD version 1 as it’s simple with no bells and whistles and it just works.....

I was using phd1 also until last year because it supported my guide cam DMK21 and phd2 didn’t.  But the ZWO camera is supported and I switched to phd2!

[Xiga]

Definitely do the belt mod Adam. I did it on my HEQ5-Pro and it helped my guiding (although i wouldn't say it was bad before). My typical RMS is usually around the 0.7-0.8 mark. Of course it can vary too, depending on where in the sky i am imaging. But if i'm getting over 1" then i'm not happy. 

Also, i use the new PPEC algorithm in PHD2. It needs a full worm rotation or 2 to settle, but the predictive nature of it should also help t lower your RMS a tad too. You can still image with it straight away (i usually do) but then after a while you might start to see the guiding settle and improve slightly over time. 

[tooth_dr]

5 minutes ago, Xiga said:

Definitely do the belt mod Adam. I did it on my HEQ5-Pro and it helped my guiding (although i wouldn't say it was bad before). My typical RMS is usually around the 0.7-0.8 mark. Of course it can vary too, depending on where in the sky i am imaging. But if i'm getting over 1" then i'm not happy. 

Also, i use the new PPEC algorithm in PHD2. It needs a full worm rotation or 2 to settle, but the predictive nature of it should also help t lower your RMS a tad too. You can still image with it straight away (i usually do) but then after a while you might start to see the guiding settle and improve slightly over time. 

Thanks Ciaran. You say yours wasn’t bad before, so I’m wondering should I try to improve things first.

When I turn off guiding the DEC line is better than when guiding, but the RA line follows a huge curve which goes off the range of the graph but comes back up again

[Adreneline]

40 minutes ago, tooth_dr said:

How is your guidescope mounted? 

Hi Adam,

Best if I attach a few photos:

When I'm feeling bold (or stupid!) I can piggy-back the guide scope on the ED80 so I can sit my ZS71 alongside and try a dual scope setup. Experience has shown I spend more time setting up than imaging! Oh for a permanent setup

HTH

Adrian

P.S. I use to spend ages trying to get my guide scope pointing in exactly the same direction as the imaging scope (I used to think of it as a finder scope!). Once I gave up on that idea life also got easier. As long as there are stars in the fov all is good!

[Xiga]

Hmm, if that's true then i would try turning off guiding in Dec and try just guiding in RA. It might help things a bit. But there's something else not quite right here. I'm setting up and tearing down each session, so with your permanent setup your guiding should be better, not worse. 

What's your PA routine at the moment? I highly recommend Sharpcap if you're not already using it. It usually only takes me 5 mins (10 at most) to dial mine in (although the very 1st thing i do when i set up is do the quick EQMod PA routine, which already gets me in the ballpark). 

I'm sure you've checked it, but what's your balance like? I have slight stiction on one side in RA so i have to balance in the other. I also had to add a bit of weight to the front of the OTA to help balance in Dec. 

Don't forget, after a meridian flip you need to re-balance. Have you been doing this? Something i haven't bothered with myself, but some people use a weight on a string trick to make sure their mount is always East-heavy. 

FWIW - the other week i had guiding issues too which ended in my 1st ever streaked image when trying Markarian's Chain. The scope was on the West side pointing lowish to the East (and now that i think about it, i almost never get to image in this position). I think my problem was balance-related, as i didn't re-position the CW. 

[tooth_dr]

6 minutes ago, Adreneline said:

Hi Adam,

Best if I attach a few photos:

When I'm feeling bold (or stupid!) I can piggy-back the guide scope on the ED80 so I can sit my ZS71 alongside and try a dual scope setup. Experience has shown I spend more time setting up than imaging! Oh for a permanent setup

HTH

Adrian

P.S. I use to spend ages trying to get my guide scope pointing in exactly the same direction as the imaging scope (I used to think of it as a finder scope!). Once I gave up on that idea life also got easier. As long as there are stars in the fov all is good!

Thanks Adrian. That looks solid. I’m also using a geoptik bar and have my finderscope held by six bolts.

Photo of mine - I’m not averse to changing holders etc if look to be potential problem.

 

 

 

[vlaiv]

Dec performing poorly when guiding as opposed when not guiding is indicative of one of these problems:

1. You are chasing the seeing. Longer guide exposures help here - don't be afraid to try out 3-4s guide exposures - you'll have more guide stars to choose from and better SNR on your guide stars.

2. There is "shake" in the mount / some parts are not as tight as they should be. Each time guide software issues a correction - even in RA, there is small - jolt to the mount that causes vibrations. If things are loose this can transfer to DEC axis as well. RA is more likely to get correction.

There is simple rule really - DEC should be getting very few corrections. Even average PA error will not require constant corrections - every 10-20s there should be small correction. If it's more than this - it can mean couple of things - wind or other kinds of shakes, or self induced shakes if parts are loose, or chasing the seeing of course.

You could try to lower guide speed. I think that one should use lower value than default of x0.5 sidereal. Go for x0.3 sidereal for example. This will lower jolts when pulse guiding.

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.

Here is drift rate calculator:

http://celestialwonders.com/tools/driftRateCalc.html

If your PA error is something like 20' - and that is a third of a degree - that is serious PA error, your drift rate is still something like 5" per minute, or 1" every 12 seconds - so if your guide period is 3-4 seconds, expected error would be about 0.3" - that should be easily corrected and would not produce more DEC RMS than about 0.2-0.3" - and this is for serious PA error of a third of a degree!

 

[tooth_dr]

13 minutes ago, Xiga said:

Hmm, if that's true then i would try turning off guiding in Dec and try just guiding in RA. It might help things a bit. But there's something else not quite right here. I'm setting up and tearing down each session, so with your permanent setup your guiding should be better, not worse. 

What's your PA routine at the moment? I highly recommend Sharpcap if you're not already using it. It usually only takes me 5 mins (10 at most) to dial mine in (although the very 1st thing i do when i set up is do the quick EQMod PA routine, which already gets me in the ballpark). 

I'm sure you've checked it, but what's your balance like? I have slight stiction on one side in RA so i have to balance in the other. I also had to add a bit of weight to the front of the OTA to help balance in Dec. 

Don't forget, after a meridian flip you need to re-balance. Have you been doing this? Something i haven't bothered with myself, but some people use a weight on a string trick to make sure their mount is always East-heavy. 

FWIW - the other week i had guiding issues too which ended in my 1st ever streaked image when trying Markarian's Chain. The scope was on the West side pointing lowish to the East (and now that i think about it, i almost never get to image in this position). I think my problem was balance-related, as i didn't re-position the CW. 

 

Im using a paid version of sharpcap. I check it if I move something or change scopes.  I’m not convinced it’s accurate, here is my results below.

Balance - I have stiction in my Dec axis making balancing difficult. RA balance is ok. I have tried perfectly balanced and east heavy.  Doesn’t get better then the graph.  I balance in 3 axis due to my dual rig setup  

 

[Xiga]

Hmm, i think you've got all the obvious bases covered. I'm not an expert in PHD myself, so perhaps others can offer more advice on how to improve performance from a software-perspective, but i think you might just have to do the belt mod and see how much of an improvement it gives you. 

You say you've already done a full strip down of your mount. How did it go? Where you confident that it all went ok, or were you a bit dubious on any part of it? 

[tooth_dr]

28 minutes ago, Xiga said:

Hmm, i think you've got all the obvious bases covered. I'm not an expert in PHD myself, so perhaps others can offer more advice on how to improve performance from a software-perspective, but i think you might just have to do the belt mod and see how much of an improvement it gives you. 

You say you've already done a full strip down of your mount. How did it go? Where you confident that it all went ok, or were you a bit dubious on any part of it? 

Its been apart 3 times in my 10 years of ownership. Each time I swear it’s the last lol.

The dec housing doesn’t turn freely when clutches are disengaged, this doesn’t affect it when engaged, but makes balancing difficult.  If I did try to fix this I’d just do the belt mod when I’m at it.

I might adjust the settings for now, maybe try guiding with one of the ED80s to see if that helps, then do the mod over the summer.