Guiding on HEQ5Pro - PHD2, PEC, or axis need adjusting?

Jasp05 (Aaron) · #1 05-06-2018, 02:23 PM

Hi guys, this is probably going to be a long post as I have a few questions, and I feel I have to explain my process so someone out there might be able to tell me where I am going wrong.

First my Setup:

Mount: HEQ5Pro (with belt mod)
50mm guidescope and ZWO Asi 120mm guide camera.
Canon 1200D (no mod) and 50-250mm Lens.

Software:
PHD2
Stellarium
Astrophotography Tool

I've only had the mount about 6 months, and have got my setup to a point where I can be setup and shooting in around 30min with polar alignment that's "good enough" for my current setup. (around 1.5-2.5 arc/sec/pixel. I believe my image scale is around 3-4 arc/sec/pixel with camera and lens setup). at either rate I don't see star trailing in my images so I'm content with that for now.

However I'm looking to get this tracking down to consistently under 1.5 arc sec as I want to upgrade to an ED80 or similar refractor. (I believe the image scale with this kind of scope and dslr will be in the 1-2 arcsec range )

Problem 1:

I polar align using the drift align in PHD2. However I find it quite difficult some nights to sneak up on a good polar alignment. And I'm not sure if it's due to the seeing conditions or some other issue.

So when doing polar alignment I pick a star near the celestial equator up high in the sky. do the drift align and make adjustments to the azimuth of the mount. Now at the start of the drift align, the PHD2 graph is generally 30arc/sec or more of error and will even out to a lower number. Once I know its still not close enough I make adjustment. Now an example of my problem is this. say PHD2 tells me I'm off by 6 arc/sec. I make a small adjustment (in the right direction

). then run the drift align. Now it says I'm 10 arc/sec out in the complete opposite direction! And if i run the drift again without making changes it could be different again.

Why do I get such variation when trying to drift align? I understand it takes very small adjustments once your down around 5 arc sec. (like just tightening the thumb screw can be enough to change things).

But is this zig zagging of being close to alignment make a minor adjustment and being wildly out, just a function of the seeing conditions? focus on the guide camera? (I believe focus is good on it and everything is mounted very tightly) or some other factor?

Problem 2:

When guiding, my mount will sometimes encounter (more so in the dec axis than RA) large blips in the accuracy of the guiding. I can run at say 3 arc/sec guiding (peak to peak) but then get areas where I could go to 5-6 arc/sec peak to peak. Some times there can be minutes of wildly fluctuating in both axis. (big spikes in both directions on the graph on both RA and DEC). Is this due to some issues with belt tension on the motors? misalignment on the worm gears? seeing conditions? I feel like it could be an issue with misalignment on the worm gears as after a few minutes things generally settle down and guiding returns to acceptable levels again.

I also have a problem where PHD2 will stop tracking. It just starts throwing full strength pulses on the RA axis but the graph doesn't respond and the guide star starts to drift in the frame from the guide camera. After I reset the guide camera pick a star again, sometimes it will work fine again. other times I basically have to disconnect all software and reopen to get it working again. (This is killing me once I'm setup guiding and leave it to run a set of shots only to come out and see it stopped guiding 10min after I left).

Problem 3:

Do I need to calibrate PHD2? I have read about the calibration process for PHD2. but haven't tried to sit down and complete it. Is it necessary? what is its function in the guiding system? And is periodic error correction worth using with PHD2?

Problem 4:

There are 2 sets of arc/sec guiding values PHD2 gives you. one is the RMS and one is the peak to peak error.

as mentioned above my peak to peak error is somewhere between 2 & 4 arc/sec depending on the night. However my RMS is generally well withing 1.25 arc/sec. and Total RMS is always under 1 arc/sec with an oscillation around 0.3-0.5.

I thought I read that RMS number around what I have is perfectly acceptable for my kind of mount. However I believe my peak to peak error can be alot better. Any information on what these values "tell you" and how they relate to the guiding is appreciated. Just so I understand whats going on a bit better. (my understanding is if the RMS is accurate that most of the light of the star will be collected towards the centre point of the star. and the peak to peak identify's the outer boundaries of the star. ie how bloated it is).

I think if anyone can help me with the above it will make my nights out observing so much more pleasant

I don't have any guide graphs to post here at the office but I will try and upload some tonight when I get home.

Thanks in advance.

Imme (Jon) · #2 05-06-2018, 02:31 PM

I use the exact same guide setup as you but on an eq6

I'd suggest dropping drift align.....I used it and it ended up being nothing but a timewaster for me. I now use Sharpcap to polar align and can easily get an almost spot on alignment in minutes.....I actually 'de-align' a little once aligned because I feel it is too close to the pole for PHD2 to work effectively.

Calibration - I calibrate everytime I move the mount during an image session....I believe the 60 seconds it take to do a calibration makes a massive difference to guiding accuracy.

Jasp05 (Aaron) · #3 05-06-2018, 03:11 PM

Thanks Jon,

I can't use the sharpcap align as I don't have Line of Sight to the SCP. (Got a big tree in the way).

Or does it not require line of sight to the SCP these days?

Imme (Jon) · #4 05-06-2018, 03:48 PM

Quote:

Originally Posted by Jasp05

Thanks Jon,

I can't use the sharpcap align as I don't have Line of Sight to the SCP. (Got a big tree in the way).

Or does it not require line of sight to the SCP these days?

That buggers that idea then....line of sight is needed

kosborn (Kevin) · #5 05-06-2018, 06:33 PM

Quote:

Originally Posted by Jasp05

I also have a problem where PHD2 will stop tracking. It just starts throwing full strength pulses on the RA axis but the graph doesn't respond and the guide star starts to drift in the frame from the guide camera. After I reset the guide camera pick a star again, sometimes it will work fine again. other times I basically have to disconnect all software and reopen to get it working again. (This is killing me once I'm setup guiding and leave it to run a set of shots only to come out and see it stopped guiding 10min after I left).

It sounds like your ASI120mm is a USB2 version? This is notorious for split frames and dropped frames and is basically unusable for guiding. I have heard that it is ok on Windows7 but my experience is that it is useless on Windows10. Check how many times PHD reports lost star.

Jasp05 (Aaron) · #6 05-06-2018, 10:36 PM

Here's a few pics from the guide logs last time I was out.

the first image is at 12.15am and was tracking like that until around 12:27 am (2nd pic) where you can see things got a bit messy. then it settles and goes erratic again a few min later. by the 12:40am mark it was all over the shop and settles for a few min before going crazy again.

So I think the mount can track well but need to find the cause of these large fluctuations.

third pic is the whole guiding graph for the night. Not my best night of guiding but unfortunately, not my worst either...

Added the guide log in a zip folder in case anyone wants a closer look. Also found a log to show an example of when the guiding is throwing out pulses but the mount is not responding.

kens (Ken) · #7 06-06-2018, 12:31 AM

Next session do a calibration near the meridian and celestial pole. Do this both before and after our drift alignment. The run the Guiding Assistant tool and follow its recommendations. Make sure you do the backlash check as there are signs of backlash in your log.
If the short runs in the log are your drift alignments they look too short for the trend line to settle. In the end you got it reasonably good at 6'. 5' is better but 6 is near enough for most purposes.

Jasp05 (Aaron) · #8 06-06-2018, 08:57 AM

I will try those steps next time I'm out Ken.

Can you explain or point out how you can tell that it may be a backlash issue from my graphs? What are the signs that make you think backlash? And if it is backlash is it worth tinkering with the worm gear meshing or belt tension to see if I can fix/ tighten it up that way ? I will wait till I've had a chance to at least run the guiding assistant and see if I can resolve any issues there before stripping the mount down (never pulled the mount apart before..)

Knowing what to look for with problems like that should help me resolve any issues in the future. (ie. I remember reading somewhere that if the graph is see-sawing up and down, that it's generally because of the seeing conditions, or trying to correct too often/ strongly).

Imme (Jon) · #9 06-06-2018, 11:28 AM

How balanced is the mount?

Looks like a flop side to side with backlash issue to me.

If it is balanced try unbalancing it a little(that's what I would try)

East and camera sides heavy is what I do.

kens (Ken) · #10 06-06-2018, 09:14 PM

Quote:

Originally Posted by Jasp05

I will try those steps next time I'm out Ken.

Can you explain or point out how you can tell that it may be a backlash issue from my graphs? What are the signs that make you think backlash? And if it is backlash is it worth tinkering with the worm gear meshing or belt tension to see if I can fix/ tighten it up that way ? I will wait till I've had a chance to at least run the guiding assistant and see if I can resolve any issues there before stripping the mount down (never pulled the mount apart before..)

Knowing what to look for with problems like that should help me resolve any issues in the future. (ie. I remember reading somewhere that if the graph is see-sawing up and down, that it's generally because of the seeing conditions, or trying to correct too often/ strongly).

Two tools that you should look at. PHDLogViewer https://openphdguiding.org/phd2-log-viewer/ and PemproLogViewer. http://www.siriusimaging.com/PEMProV...up_1.2.1.0.exe
Using PHD Log Viewer you can the sawtooth shape on the Dec graph that is characteristic of backlash and stiction. PHD2 issues guide pulses but the mount does not at first respond then flips to the other side and you start over. Without backlash and 90% aggression one pulse should take you back near the centre

Jasp05 (Aaron) · #11 06-06-2018, 09:50 PM

So I went out tonight and did the calibration at the meridian but realised I did it at the north end and not close to the pole. (clouds had rolled in and finished my night by the time I realised)

anyway attached is the calibration log / data. I'm assuming looking at it those 2 lines are meant to track back on exactly the same path which means I got problems.

However after doing the calibration and then just let it guide after the calibration the next image was the result. Before I was polar aligned mind you. (tbh that's better guiding than I was getting AFTER I was aligned previously

)

Anyway as mentioned above clouds stepped in and ruined my night before I could re calibrate or polar align. So will try again soon. but based on tonight's messing around I think a proper calibration and new alignment, along with some tinkering with balance of things, I might just end up where I need to be without opening the mount up.

Jasp05 (Aaron) · #12 06-06-2018, 09:53 PM

Quote:

Originally Posted by kens

Two tools that you should look at. PHDLogViewer https://openphdguiding.org/phd2-log-viewer/ and PemproLogViewer. http://www.siriusimaging.com/PEMProV...up_1.2.1.0.exe
Using PHD Log Viewer you can the sawtooth shape on the Dec graph that is characteristic of backlash and stiction. PHD2 issues guide pulses but the mount does not at first respond then flips to the other side and you start over. Without backlash and 90% aggression one pulse should take you back near the centre

Hi Ken,

To remove the backlash or stiction is that something that requires tinkering with the worm gear meshing and lubrication in the mount? Or can this be resolved with just altering the balance of the load on the mount?

luka · #13 06-06-2018, 10:03 PM

Removing the backlash requires messing with the gear meshing. It is not too difficult and there should be guides on the net.

But you should use the guiding assistant to measure the DEC backlash first and see how big it is. Even with larger backlash you can guide in one direction only, that is what lots of us with this class mounts (HEQ5 and NEQ6) are doing.

Basically have the DEC polar alignment slightly off so that the corrections always need to be carried one way. Then instead of Auto you only correct North or South. It is also important to keep the DEC axis slightly off-balance.
And you should keep your RA axis always East heavy so that the gears are always slightly loaded. That would avoid the backlash problems.

kens (Ken) · #14 06-06-2018, 10:46 PM

Quote:

Originally Posted by Jasp05

So I went out tonight and did the calibration at the meridian but realised I did it at the north end and not close to the pole. (clouds had rolled in and finished my night by the time I realised)

anyway attached is the calibration log / data. I'm assuming looking at it those 2 lines are meant to track back on exactly the same path which means I got problems.

However after doing the calibration and then just let it guide after the calibration the next image was the result. Before I was polar aligned mind you. (tbh that's better guiding than I was getting AFTER I was aligned previously

)

Anyway as mentioned above clouds stepped in and ruined my night before I could re calibrate or polar align. So will try again soon. but based on tonight's messing around I think a proper calibration and new alignment, along with some tinkering with balance of things, I might just end up where I need to be without opening the mount up.

That calibration issue could be the result of poor polar alignment. Make sure you use the calculator on the Guiding tab of the brain to calculate a suitable calibration step size. You've got few too many there so the steps are too small.
You were correct to calibrate nearer the equator (to the north). You cannot calibrate at the pole.