PHD2 - Calibration Errors and Strange Guiding

[Toxophilus]

I hope someone can shed some light on this problem that I'm encountering. I currently have a Meade LX90 classic EQ mounted on a wedge with an Orion ST80 mounted as a guide scope. I have added an ADM balance kit and the balance of the setup looks pretty good. I have polar aligned my scope and got fairly good go to accuracy out of it, then drift aligned it (as best I can in RA (see later))  and more or less spot on for Dec. I have trained the scope etc. but I still keep getting failed calibrations (in fact I have never has a successful calibration) and an odd behavior when just accepting the calibration and letting it guide anyway.

Here is an example of the calibration error that I'm getting:

and this is what is happening when I let it guide:

I'm not sure that this run was particularly well set up, but I have had better Dec guiding that this. However its the RA figure that I can't get to be sensible.

Every time I run a guide it seems that the telescope is either running (I think) too slow by 15" or so. I have tried training for PE but that did not seem to help (although admittedly I need to re-try it). I have also tried various custom tracking rates which seems to have no real effect on the issue. I'm running the scope on a regulated mains adapter, so I cant see it being a power issue. It seems that PHD is having to drive the RA rather than correct for errors, which is leading obviously to frustratingly poor images. I have tried everything that I can think of to get my guiding better but have simply run out of Ideas other than removing the OTA and putting on a Skywatcher NEQ6 pro or similar. A route I just don't want to go down at the moment as I like the LX90 fork mounted and although the LX90 is not the perfect AP machine, I should at least be able to get 5 minute subs.

Any ideas/suggestions are welcome as I have run out of ideas.

[Astrosurf]

I'm no guiding expert, but I use the original PHD and it's great. So many people have issues with PHD2 that I hope never to have to use it!

Alexxx

[kalasinman]

Try RA agression to 100, min mov in RA to .05, hyst to 0

[Toxophilus]

I used PHD 1 originally and got the same issue. In fact that is why I moved to 2 as I thought that it may be an issue with it. But I'm convinced that it's an issue with the mount (I suspect a motor, clutch or gear issue  ) . I'm just hoping someone has seen this before and can confirm or direct me to a solution.

[Leveye]

In my case this kind of graph is almost always caused from the mount not being level, aligned and balanced properly before a calibration run and then drift alignment is done. I'd check all that first. Use the auto exposure setting when calibrating and a higher RA and DEC max duration. Personally I've had no issues with PHD2 or any of it's updates since it came out. Andy and co are really on top of the updates for it and listen and respond quickly to any issues.

[glowingturnip]

looks weird doesn't it, as you say as though PHD is actually having to do the driving of RA (in fact of both axes). 

If you just turn the guiding off and just watch the screen, does the star eventually drift away ? 

[Toxophilus]

In my case this kind of graph is almost always caused from the mount not being level, aligned and balanced properly before a calibration run and then drift alignment is done. I'd check all that first. Use the auto exposure setting when calibrating and a higher RA and DEC max duration. Personally I've had no issues with PHD2 or any of it's updates since it came out. Andy and co are really on top of the updates for it and listen and respond quickly to any issues.

I'm pretty sure that the scope is level, certainly to a reasonable degree. I will get a big spirit level out and double check next time. Which actually raises one thought. What is the best way of checking that an LX90 is level? I have used a level on the tripod base and then put the wedge and telescope on and also tried leveling once the telescope and wedge are in place, but when you do this there are so many bolts and uneven surfaces that you can't use a big level to check and have to rely on the little bubble that Meade supply on the wedge. 

[Toxophilus]

looks weird doesn't it, as you say as though PHD is actually having to do the driving of RA (in fact of both axes). 

If you just turn the guiding off and just watch the screen, does the star eventually drift away ? 

Yes is does, at quite a noticeable rate too.

[glowingturnip]

Yes is does, at quite a noticeable rate too.

it's got to be a telescope misalignment then, rather than a PHD problem, hasn't it ?

I've not got any experience with wedges, but are you sure it's polar aligned ?

Either that, or as you say your tracking rates are off

[Toxophilus]

Yes is does, at quite a noticeable rate too.

The one thing that I have not been able to completely work out is: is the mount driving too fast or too slow. It is consistent in one direction by about the same amount though.

[Toxophilus]

it's got to be a telescope misalignment then, rather than a PHD problem, hasn't it ?

I've not got any experience with wedges, but are you sure it's polar aligned ?

Either that, or as you say your tracking rates are off

I use the kochab clock method of initially aligning (I usually get the autostar report that I'm with in 5' of pole (its minimum accuracy report message) or only slightly off) and then try to drift align, however the drive rate issue that I seem to have makes it almost impossible to align for RA.

[glowingturnip]

The one thing that I have not been able to completely work out is: is the mount driving too fast or too slow. It is consistent in one direction by about the same amount though.

i guess you could experiment - if you gave the top of the tube a gentle nudge westwards, then if the star is displaced in the same direction as the drift then the motors are driving too fast, but if it's in the other direction, they're driving too slow.

Just for a sanity check, it is driving in sidereal tracking rate isn't it ?  Not solar rate (slightly slower I think) or lunar (definitely slower)

[Toxophilus]

i guess you could experiment - if you gave the top of the tube a gentle nudge westwards, then if the star is displaced in the same direction as the drift then the motors are driving too fast, but if it's in the other direction, they're driving too slow.

Just for a sanity check, it is driving in sidereal tracking rate isn't it ?  Not solar rate (slightly slower I think) or lunar (definitely slower)

I definitely have it on Sidereal tracking. In fact I have even tried using custom tracking rates to see if that helped and it made little or no difference.

[Xplode]

I'm no guiding expert, but I use the original PHD and it's great. So many people have issues with PHD2 that I hope never to have to use it!

Alexxx

The problem seems to be the settings in most cases and many just stop using it because their graphs doesn't look as nice as they did in PHD.

PHD2 can be set to give graphs from pixels and arcsecs, if set to arcsecs it usually looks much worse than if set to pixels and i think many don't notice this and think their guiding is worse.

PHD usually works ok right after installing, but PHD2 need a little setup which the wizard takes care of if all settings are input correctly.

One setting where it's easy to miss is the calibration step size, many seem to go for the wrong setting for guide speed so the calibration step is calculated wrong which usually result in too short calibration step and calibration taking very long time or doesn't finish.

[michael8554]

First of all, not set to Southern Hemisphere is it?

As an indication of your tracking speed, how long does a star stay in the FOV of a longish eyepiece - without guiding of course?

Alternatively, set any hour mark on your RA scale against a mark on the scope base and  leave the scope tracking for an hour. The next hour mark on your RA scale should then be opposite the mark you made on your base if your tracking rate is correct. 

Michael

[Toxophilus]

First of all, not set to Southern Hemisphere is it?

As an indication of your tracking speed, how long does a star stay in the FOV of a longish eyepiece - without guiding of course?

Alternatively, set any hour mark on your RA scale against a mark on the scope base and  leave the scope tracking for an hour. The next hour mark on your RA scale should then be opposite the mark you made on your base if your tracking rate is correct. 

Michael

Cheers Michael. I cant see a southern/northern hemisphere in the autostar controlled but you have to enter longitude and latitude for a site so I think it works it out from there. However I'm running your experiment over 4 hrs just to confirm if the tracking rate is out and if so in what direction.

[lensman57]

This is a polar alignment issue. Check your PA.

A.G

[Leveye]

I'm pretty sure that the scope is level, certainly to a reasonable degree. I will get a big spirit level out and double check next time. Which actually raises one thought. What is the best way of checking that an LX90 is level? I have used a level on the tripod base and then put the wedge and telescope on and also tried leveling once the telescope and wedge are in place, but when you do this there are so many bolts and uneven surfaces that you can't use a big level to check and have to rely on the little bubble that Meade supply on the wedge. 

Take everything in steps...You need to concentrate on the tripod with the base for the mount being as basically level and polar aligned as possible first. Remember to point it to your "true' position and not magnetic! That can be over 15-20 degrees off right there. Then level perfect with the mount on. Then put the scopes on and balance it. (in my case i go just east heavy to mesh the gears proper). Using your lightest rig will make it easier to adjust the mount's az and alt knobs. Then you do a basic slewing for either az or alt. I did mine at about 25-35 degrees on each and for az I was just ahead of the meridian. Calibrate using PHD2 and then DA.

[davedownsouth]

Are there any rules for what guide rate to use for a given mount / scope?

Sent from my iPhone using Tapatalk

[Toxophilus]

Cheers Michael. I cant see a southern/northern hemisphere in the autostar controlled but you have to enter longitude and latitude for a site so I think it works it out from there. However I'm running your experiment over 4 hrs just to confirm if the tracking rate is out and if so in what direction.

Well, I did a little test over the weekend. I left my scope running for 10 hours, having zeroed it on one of the RA marks and loaded it up with cables, cameras, etc. After 10 hours it had gained about 1.5 minutes, which if my maths is right means that per second I'm running about 0.0375" too fast, something that would probably not even show up on a 30 second guide and on a 5 minute guide would only amount to 22.5". Something that autoguiding should easily take out. No where near the 15" or so that was being reported by PHD, so I'm happy that the mounts guide rate is OK.

So I'ts back to basics and re-check my polar alignment and try to come up with a methodology that allows me to get it consistently right. I actually suspect my level is the culprit so I'm going to get a new spirit level and see if that makes a difference and my current ones are a bit old and if the bubble has shifted then that could be the root of my problems. 

[glowingturnip]

how are you getting the initial polar alignment btw, are you using a polarscope and can see Polaris ?

Had a total numbskull moment when we were trying to align my sons' school's EQ8 which doesn't have a polar scope - had a miserable time trying to drift align it, and then eventually realised that I'd initially set the Alt of the mount to 90-latitude, so that it was about 22 degrees out, and hadn't noticed - sheepish or what.  Of course it went much quicker once I'd spotted that.

[Toxophilus]

how are you getting the initial polar alignment btw, are you using a polarscope and can see Polaris ?

Had a total numbskull moment when we were trying to align my sons' school's EQ8 which doesn't have a polar scope - had a miserable time trying to drift align it, and then eventually realised that I'd initially set the Alt of the mount to 90-latitude, so that it was about 22 degrees out, and hadn't noticed - sheepish or what.  Of course it went much quicker once I'd spotted that.

Unfortunately I don't have a polar scope. So I'm using Kochab's clock to get polar alignment. Unfortunately it can be a bit hit and miss getting it right. Although As I have my finder, guide scope and main scope all aligned very accurately, So the trick that I'm planning on trying out is using an illuminated reticle on my ST80 that will give me a FOV that should put Polaris about 1/5 from the edge of the FOV. If I then rotate the scope and it rotates around the FOV evenly then I'm guessing that I should be somewhere near pole. I'm suspect that I will be forced into buying one eventually. Do you know of any that work well with the LX90 all of the ones that I have seen have been designed for GEM mounts.

[glowingturnip]

ahh, it's an alt-az on a wedge isn't it - I wouldn't be able to advise I'm afraid.  The idea of rotating with Polaris in the fov sounds like a good one though, to get an initial align.

[Toxophilus]

ahh, it's an alt-az on a wedge isn't it - I wouldn't be able to advise I'm afraid.  The idea of rotating with Polaris in the fov sounds like a good one though, to get an initial align.

Yes, I'm afraid that its on a wedge. I have found the polarmate but that requires you to mount the telescope onto the wedge, whereas I prefer to keep my scope on the wedge and put the wedge and scope onto the tripod. I feel safer doing things that way. However if all else fails I will get a polarmate and change the way I set up. It will make storage of me scope a little easier.

[Freddie]

Putting it on a wedge in effect makes it an EQ mount so being level or not doesn't matter.