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Old 02-01-2018, 11:43 PM
Jasp05 (Aaron)
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HEQ5 Pro and PHD2 Guiding

Hi guys,

I recently got the HEQ5 Pro mount and have been using a 50mm guidescope and asi 120mm guide camera.

I was wondering how much movement on the PHD graph is ok?

I can drift align for 5 min using the DARV method. and the guiding seems pretty good, (within 1" or 2" either side so within 4" total.) Sometimes will peak to 4 but it corrects itself back generally. Doesn't happen often.

However say i move to a different target. (I use stellarium for this). The guiding graph starts to go a bit haywire depending on the object I'm looking at. for reference I've been taking some widefield shots of orion and eta carinae with dslr and lens at 200mm.

It will start to make huge corrections in dec, or the RA is not moving around the 0 point but instead is averaging around the -1" mark.

Any ideas as to how I can fix this? I don't think its a huge problem as the shots have still been pretty good. (at least compared to what I got with my homemade tracker with no guiding..)

Will try to post an example PHD2 graph but its on my other laptop.

But any info on what limits an acceptable graph should move between would be nice. gives me a reference to aim for when I'm guiding. (although I guess if the pictures are good it's fine right )
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Old 03-01-2018, 12:50 AM
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RobF (Rob)
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Hi Aaron

Just to get yourself "in the ballpark" for allowable error, suggest:

- ensure you have FL and guidecam pixel sizes set ok
- put PHD2 into arcsec on the guiding graph (not pixels)
- calculate arcsec/pixel for your main imaging scope/lens and camera


Then make sure your worst guiding error isn't much over your main scope/camera arcsec value (well under is nice! )


As to how much is to be expected, can also depend on:
- wind
- balance of scope/mount (sometimes a bit overbalanced in DEC and RA is better)
- seeing (scintillation of guide star)
- flexure between main scope and guide scope


Just taking a stab from what you've described you should hopefully have most of your DEC and RA tracking error between plus/min 2 arcsec, although for lens imaging suspect 3 or even 4 arcsec may not affect your final image appreciably.


Hope this is a starting point,

Rob
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Old 03-01-2018, 08:38 AM
kens (Ken)
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In addition, you want your guiding pixel scale to be no more than about 4x the imaging pixel scale.
You didn't say if you are using ST4 guiding (PHD2 "On Camera" mount) or pulse guiding through ASCOM. If you are using ST4 guiding you need to calibrate PHD2 on each target. If pulse guiding you should first calibrate near the meridian at dec 0 and tick "Autorestore calibration" on the Guiding tab of the Brain.
Its better to post the guide log rather than screen shots. It sounds like something is not quite set up properly.
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Old 04-01-2018, 01:31 AM
Jasp05 (Aaron)
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So I'm currently using a Canon 1200D and 55-250mm efs lens.

The Arcsec/pixel of the dslr and lens at max FL is around 2.21"/pixel (I used FL of 400mm as my dslr is a crop sensor - 250mm x 1.6 crop factor)

my guide scope and guide camera combo comes up with 4.77"/pixel.

So I guess I'm within your guidelines of the imaging vs guiding pixel scale.

I've attached my guiding graph below. This is probably the best guiding i have got yet with the mount. (Is it good? Could it be better? If so how? )

I'll have a dig for the guide log of that night also.

I know I haven't touched any settings in PHD2 yet so I'll be sure to set that Auto restore option. I am using Ascom Pulse guiding btw.

And when you say calibrate at the meridian first? I start my first drift alignment from there yes? or is there some calibration function in PHD?
Attached Thumbnails
Click for full-size image (First nightguiding results - heq5pro.jpg)
122.8 KB69 views
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Old 04-01-2018, 01:45 AM
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That looks fine for a typical chinese mount Aaron. The ultimate test is that you're getting round stars on your longer exposure images?

You might reduce the noise a little with mount tweaks (cleaning, adjusting, bearing, belt mods) and twiddling PHD settings, but you have very little DEC corrections on that graph (good!), and almost all the RA corrections are in the same direction (consistent with typical periodic error curve over part of a worm cycle).

Not helpful, but the best sure way to get even better tracking (if you ever need it) is to buy a mount that is 5-10 times more expensive!
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Old 06-01-2018, 10:38 PM
Jasp05 (Aaron)
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Hi again guys. I'm out with my mount again and having some issues

My dec axis seems to be making some really wild corrections. (more than 3").
I think that may be due to some stiffness in that axis. so will have a go at playing with the worm gear meshing on the dec gear later.

But the main question i have tonight is, If i track on something far from the pole like pleiades, it tracks pretty good. However If i go for something nearer the pole, (the LMC) the RA axis is trying to make big corrections. (on the order of 12").

I have drift aligned for 5 min at 400mm FL. I used the star Menkar for the meridian point. and Procyon for my eastern drift for altitude.

Any ideas as to what may be happening??

Edit: I slewed away to another object and back and the tracking seems to be under control again. Why does guiding have to be so finnicky??

Last edited by Jasp05; 06-01-2018 at 11:06 PM.
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Old 07-01-2018, 12:04 AM
kens (Ken)
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Can you post the guide log? Its under Documents\PHD2 and contains a wealth of information that can help with diagnosis
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Old 07-01-2018, 11:32 AM
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Quote:
Originally Posted by Jasp05 View Post
Why does guiding have to be so finnicky??
Alas, this is a fact of life for many chinese mounts. Just when you think you've got it conquered an amalgamation of wind, worm/gear/bearings, seeing or balance combines in some new diabolical way to confound.

I find myself often tweaking PHD2 settings after an hour or two each night to try and best fit the conditions you're dealing with. Even within a night seeing can change rapidly.

As a general rule, guiding closer to the celestial poles does become more of a challenge.
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Old 07-01-2018, 11:37 AM
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Merlin66 (Ken)
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Aaron,
If you've managed to get the polar alignment set close, then there should be no (or very little) corrections in Dec.
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Old 08-01-2018, 03:59 PM
Jasp05 (Aaron)
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Declination is where the biggest adjustments are made on my mount Ken.

And if I've drift aligned for 5 min at 400mm FL that should be reasonably close to decent PA?

Or should I drift align for 10min +? I only do 60sec to 3 min subs generally so figured 5 min drift should be fine for my purposes? (shorter alignment time also).

I know the Dec axis was binding in a spot or 2 whilst being used with the hand controller at high speed. But haven't seen any issues since I've started guiding. (No I haven't tinkered with the drive gears yet, as its a new mount and kind of wanted to get a base line for tracking accuracy before I go tinkering. )

I'm considering building a pier to mount it on at home and save myself the dramas of all these finicky problems that arise with each setup and tear down. But then I deprive myself of the nights out at a dark site with the mount.

Should I do a full run over the entire worm drive to let the PEC be able to do some work and alleviate some issues?


I know last night, my guiding was terrible for some unknown reason for the first hour or 2. Then I changed to a smaller FL lens and my guiding suddenly was under 1" arcsec +/- in RA while dec was still dancing around.
(I don't think it had anything to do with the smaller lens as there was very little breeze/ weather effects to bother the setup. )

So I assumed it must of been a bad part of the drive cycle that I was in and suddenly came across a nice spot. thoughts?
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Old 08-01-2018, 04:51 PM
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Aaron,
You're already using PHD2 - use the PA alignment feature built into PHD2.
Honestly, you shouldn't even be aware of the Dec axis during guiding.

Double check that your mount balance is good; a slight out of balance towards the East in RA and similar on the Dec towards the South.
This should help suppress random movements.....
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Old 08-01-2018, 10:55 PM
Jasp05 (Aaron)
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Didn't know phd had a polar alignment tool. I can't see the stars at the scp to use anything but drift alignment.

And how do you ensure your guidescope is aligned with the mounts axis of rotation? I'm using a custom dovetail bar to mount a 50mm finder scope and dslr.
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Old 08-01-2018, 11:51 PM
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Aaron,
PHD2 uses the drift method...
See under the PHD2 Help tab, "Tools and Utilities"/"Drift Align" for details.
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Old 08-01-2018, 11:57 PM
kens (Ken)
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The main PHD2 PA tool uses drift alignment.
You don't need to align the guidescope to the axis of rotation. Even the new Static PA tool (which requires the SCP to be visible) does not require that as it can calculate it from the movement of the guide star as the mount is rotated.
When you say you can't see the star at the SCP I assume its due to trees or buildings. If its just because they are faint to the naked eye that's not a problem for a camera.
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Old 09-01-2018, 10:48 AM
Jasp05 (Aaron)
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Yeah I have got some big trees right in the way of my view south.

I might try the PHD2 drift align tool then. I have been using the D.A.R.V tool inside APT for drift aligning with my dslr.

Which method would be more accurate? I'm assuming PHD using your guidescope and camera to drift align? or is it using my imaging camera and lens? (didnt think PHD could connect to dslrs?)

My guidescope FL is only 162mm compared to 250mm on my DSLR Lens. So I would have thought drift aligning at 250mm would be more accurate?
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Old 09-01-2018, 11:08 AM
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Merlin66 (Ken)
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Using PHD for drift alignment would be as accurate as the PHD guiding...
Should do the job for you.
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Old 10-01-2018, 12:39 PM
Jasp05 (Aaron)
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I tried out the PHD2 alignment tool last night. Works quite well. Allows for fast basic alignment.

However the one problem I did have was that it would average down to a nice low number, stay there for a while then jump back out again. Is this meant to happen?

I never took any screen shots and can't remember numbers off hand. But closest I got the azimuth to was around 1', where it sat after a 1 min or so.

The altitude though was all over the place. couldn't get it to stay stable. got it with 2-5' and then it would start spiking to 20'+. this is after a min or so. The first 30 sec were all over the place then it settled down to that 2-5' then another 30sec would pass and it would spike again.

I gave up and thought I'd try guiding with the best I could get and it was the best guiding in RA I've had since I got the mount. However the DEC has some big periodic issues. ( I believe they are periodic as they occurred at roughly the same time interval and to the same peak. looked like a pattern repeating). The Dec was making corrections every sec to try and keep it under control.

The Ra was good for most of the night but after an hour or so it started to peak in a bit of a pattern also. (was only making a correction every 5-10 sec though so I thought a small adjustment here and there is an improvement compared to my previous nights).

Is it possible that there are parts of the drive where things are butter smooth and then bits that are rough? As in the worm drive engages nice and smooth on some portion of the drive gear and not others? Or is it generally bad all around if there's a problem?

So I think I need to set aside some time and play with the belt tension and worm drive meshing on both Dec & RA.

But all the same I was taking some 60 sec subs of orion and they came out pretty good still. Pic attached. About 20min worth of 60sec exposures at 800 iso. Few darks taken and stacked. Touched lightly in Lightroom & Cropped (The lens has bad distortion at the edge of the frame. and the stars seem a bit out of focus. Really struggle to have this lens hold focus. It likes to keep a small tail/ flare on the stars)
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Click for full-size image (Orion Nebula.jpg)
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Last edited by Jasp05; 10-01-2018 at 12:50 PM.
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Old 10-01-2018, 12:44 PM
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Merlin66 (Ken)
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Hmmm,
Next try with the Dec corrections switched off - see what happens.
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Old 10-01-2018, 03:56 PM
Jasp05 (Aaron)
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I assume you mean while guiding?
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Old 10-01-2018, 03:56 PM
Jasp05 (Aaron)
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And how do you calibrate PHD2? is that something I should be doing every time I setup? or is just a once off thing?
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