Yet Another Newbe - with an LX200

[Jack Thewlis]

I recently got my twentyfive year old LX200 mounted onto a heavy duty wedge and am seeking any advice you guys can provide on how things are progressing. It's early days and I'm barely on the first rung of the ladder. The first hurdle I have is that there's only a southerly view from the mount. It's located near a high wall which blocks out the pole and everything else to the east and west of it  It's a very poor location, but I live with it. Anyway after a guesstimated polar alignment using a shadow from the noon sun, a spirit level and a protractor, I adjusted the mount to within a degree or two of the pole. These old Meades won't accept pulse guiding, so I use the ST4 connection from the camera and Aux Mount with the ASCOM driver. Using PHD2 with the default values for everything, I did a first calibration just to confirm the axes actually would drive and to enable me to do a Drift Alignment. The calibration popped up a backlash warning that I ignored at this stage. I needed to make some basic adjustment of the wedge.

From my naive perspective, the Drift Alignment went pretty well and I managed to set it to within five arc minutes of the pole. That done I decided to reitterate the calibration and Drift Alignment on the following night. Both seemed to go better than previously and the Guiding Assistant made several recommendations, which I acted on. The alignment now seems to be within two or three arc minutes. So, I've uploaded the logs from my latest session in the hope that you'll have some encouraging comment. The visualisation tool confirms a colossal backlash issue in the Dec drive which I might be able to tackle by adjusting the worm tension. However, I fear it's more likely within the primitive plastic gearbox that turns it. To my eye, the guiding looks quite atrocious and I've no idea if anything can be done to improve it. I should read the manual completely, but right now I could use some encouragement.

My rig consists of
Meade 10" LX200 (f10) with an f6.3 reducer/field flattener and an Ha, Hb, Oiii narrowband filter.
ZWO ASI 224 colour camera for imaging.
60mm guide scope focal length 280mm
ZWO ASI 120 mono camera for guiding
Meade fork mount on heavy wedge/pier

I saved the logs to a flash drive so it was convenient to upload them to the cloud.

Guide Log

Debug Log

Many thanks,

Jack Thewlis

[Michael 8554]

Hi Jack

Both the logs you posted are DEBUG logs, no GUIDE log that I can see.

I have a LX200GPS, which I have had permanently pier mounted for nearly 5 years.

I have adjusted PA down to 5 arcmins, which is as good as you need to be for guiding, according to the developers.

But if you have the standard Meade wedge on your 10", you will find it is not rigid enough, so PA will mysteriously change on its own.

I could fine-tune my PA but just slightly loosening or tightening the adjustment bolts, even with the lock bolts tightened, that's how much the wedge bends.

I have a replacement wedge made from 20mm steel.plate.

It has Dec Backlash which I have been unable to get good enough. 

On the LX200 Classic that you have, there was a diy mod to adjust the Dec worm tension on the fly, with an adjusting screw protruding through a hole in the arm containing the dec motor.

On my GPS, which is different, I adjusted the tension until the motor started to labour on slow slews, then backed off a tad.

You will need a 2D (or is it 3D ?) balance system mounted on a rail under the OTA.

You point the OTA horizontally with the Dec lock off (careful it doesn't nosedive) and adjust the weight along the bar until it's balanced.

Then point at the zenith and move the weight outwards or inwards relative to the rail until it's balanced.

Then attach lead fishing weights on either arm to get balance when pointing east and west.

But ultimately you will have to Dec guide in one direction only - tricky if you Dither in Dec too.

So with PHD2 running, check the Trend line and see which way Dec is heading due to PA error.

Then balance the scope to be slightly heavy in that direction.

Then set Dec guiding to correct in the opposite direction.

Hopefully Dec will not need correction in the other direction, which will take a long time to correct due to the backlash.

Always before Calibration, apply some North pulses with the handset, until you see the guidestar move, which shows the backlash has been taken up.

Also worth Training Periodic Error.

Don.t have the Dec Backlash Comp set on the mount, it conflicts with the PHD2 Dec Backlash Comp.

That's enough for now, I could go on and on........

Michael

Wiltshire UK 

[Jack Thewlis]

Hello Michael,

Doh, sorry, I'll try that again.

Guide Log

Debug Log

Cheers,

Jack

[steve]

Hi

Pixel scale wrong. 120mm = 3.75.

I think to stand a better chance, maybe try an off axis guider.

Good luck, clear nights and stay safe.

Cheers and HTH.

Steve

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[steve]

** correction. Pixel scale OK. Pixel size 3.8 is near enough.

Sorry

[Michael 8554]

Hopefully the developers will chip in.

Looks like Periodic Error needs taming.

Only about 10 minutes of unbroken guiding to go on.

Improve guidescope focus using the HFD  reading on the Star Profile window, aim for values of 3 to 4.

Michael

Wiltshire UK

[Jack Thewlis]

Hi Steve,

The 3.8 is the result of PHD2 rounding up the detected 3.75microns from the camera.

I presume this is what it does?

Cheers,

Jack

[Jack Thewlis]

Hi Michael,

OK will look at the focussing. The HFD seems to vary with each exposure. Sometimes it's below 4 then above 4 at each refresh. I suppose bad seeing plays a part here?

The RA worm period is 9 minutes. Does the 10 minute log implicate that or some other periodic effect?

I'll run a longer test guide tonight hopefully and see if this sheds more light.

Cheers,

Jack

[Jack Thewlis]

I managed to get a couple of hours or so of guide log tonight which will hopefully provide a better picture of where things are standing. The logs show two or three short sessions during which I experimented with the RA aggression with a final run of a couple of hours at default values plus the adjustments recommended by the GA. What I failed to achieve tonight was a better focus. No matter what, I couldn't get the HFD below 4 and it persistantly varied between 4 & 5. I guess this has an impact on the guiding efficiency. I didn't attend throughout the final run and there some unexpected scattered cloud events leading to momentary star loss. These recovered automatically until the final event at which I terminated the run. Here's what I got:

Guide Log

Debug Log

Any advice will be most appreciated.

Cheers,

Jack

[Michael 8554]

While I think of it...

Do NOT run the mount with an 18 volt supply, which Meade switched to from 12 volts.

The capacitors on the boards were not rated high enough and shorted with age.

Worth replacing yours anyway before they go and wreck the boards, very expensive problem.

Plenty of online detail Meade LX200 Classic Capacitor Replacement.

Michael
Wiltshire UK

[Jack Thewlis]

The scope has a 12v switching power supply and the usual suspects have been replaced.

Do you see any hope in my latest logs?

Cheers,

Jack

[Michael 8554]

Hi Jack

Where are you based ?

I can only comment on obvious errors, so I should leave the finer details to Andy, Bruce and Co.

Your final guide session - you can see Dec yoyo-ing back and forth about +/-5arcsecs. To me this means your balance was too good. If the scope was slightly heavy one way it wouldn't wobble between the limits of the Dec Backlash.

RA on the last session is moving +/- over 2arcsecs. PHD2 corrects, but it takes a lot of pulses, suggesting Aggression is too low. But it then overshoots, which suggests too much Aggression. So could be due to fast blips in your Periodic Error, which are difficult for PHD2 to follow,  really I'm guessing here so hope Andy and Co take over :->

Michael

Wiltshire UK

[Jack Thewlis]

Hello Michael,

I'm currently under Covid-19 lockdown, North Yorkshire where a few more clear nights would make it more tolerable. Yes, I noticed the way the drives are performing and wondered about aggression. (which I assume behaves like it sounds). I raised it tentatively a couple of nights ago, but after a few minutes thought better of it. With only a rudimentary understanding of PHD2 settings, I thought it best to stick with defaults and any suggestions from the GA. I'll look at that again I think. The clue seems to be let it run for an hour or so before making any conclusions on a parameter change.

I'll be somewhat surprised if the dec balance is anywhere near perfect, but perhaps so. The scope is pretty weighty anyway, so landing on the desirable sweet spot seems to be more good luck than good management. I've managed the RA axis to be east heavy, perhaps too much so, but I await any observations that might confirm that. As far as guiding goes, both the scope and myself are straight out the box, '95 and '43 vintage respectively.

I think the seeing has thus far been very average. The last run was done at HFD well above 4 sometimes up to 5, so that will imact the precision no doubt. In fact the stars actually had a very thin halo around them, quite some distace from the centre, so I've now added an IR block filter to the camera in case.

As for periodic errors, I've never looked at it I'm afraid I read Meade's manual back in the day and decided I'd rather stick to visual use than spending hours trying to teach the PEC controller manually. What PEC training apps do you recommend?

I'll certainly welcome any further comments from the gurus whenever they're around.

The weather here is due to worsen I think ,so maybe a few days before I can fire it up again.

Cheers,

Jack

[Brian Valente]

Hi Jack

>>> What PEC training apps do you recommend?

PEMPro is the gold standard for periodic error software

Brian

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Brian 

Brian Valente

portfolio brianvalentephotography.com 

[bw_msgboard]

Hi Jack.  It’s hard to identify the real source of the problem here.  I’m sure you know these scopes were never designed for the kind of imaging we do now and I think you should have modest expectations about how well yours will perform.  It seems to me you’ve done a lot of good things and have handled the basics.  Let’s take a look at a section of the Dec behavior in one of the GA runs you did:

 

 

Look at all the fast, frame to frame movement of the guide star, keeping in mind the Dec motor is not running.  You can see there are many times when you get 3 arc-sec movements on a rapid basis.  This is much too quick to be able to guide out.  So it’s not surprising that your guided sessions would show a Dec guiding RMS of 2.6 arc-sec, it would be very hard for it to be smaller.  So where does this come from?  The likely answer is seeing conditions, keeping in mind that conditions right around the scope can contribute more than the high-altitude effects discussed in web-based seeing forecasts.  It could conceivably also come from vibration anywhere from the ground up to the guiding assembly but I think it’s probably seeing.   Long focal-length imaging like what you’re trying to do is hard and you are particularly vulnerable to bad seeing conditions  - and my understanding is that  the UK is well-known for having poor seeing.

 

In the meantime, you really need to stop flogging the guiding parameters because guiding isn’t going to deal with any of this.  But if you have the settings goofed up, you may not be able to take advantage of better conditions when they do arrive.  I recommend resetting all the guiding parameters to their default values.

 

With regard to the uncorrected RA periodic error in your mount, I’d be surprised if the pre-GPS Meade mounts supported permanent periodic error correction.  I really think you are bumping up against the limits of trying to use a 25-year old mount that was never well-suited for imaging even when it was new.  No offense intended, that’s just my 2-cents worth as an owner of a 2003 LX200GPS.

 

Cheers,

Bruce

 

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[Michael 8554]

It has been very windy here in the UK, so I should have suspected seeing was the cause of the spiky graphs.

So Brian, wait until the winds die down, reset PHD2 to the presets, do a new Calibration after nudging North, do a 5 minute Guide Assistant run and accept the changes, then Guide for 20 minutes without further changes to the settings, and post the logs. 1.5 to 2 sec exposures perhaps.

I seem to remember that the Classic has stored PEC that could be learned and updated, and a search confirmed.

This large site was the pinnacle of LX200 Classic facts and figures, and Doc G particularly employed very precise scientic methods in his research and implementation. His methods of beating Diff Flex were legend.

Another suggestion for long FL guiding is Off Axis Guiding, I found the ZWO ASI 120MM was not sensitive enough to immediately find a star when on target.

http://www.skymtn.com/mapug-astronomy/MAPUG/SmartDrv.htm

Michael
Wiltshire UK

[Jack Thewlis]

Hello Bruce,

Thank you for your input and advice.

For the run in question, everything was set at default (maybe a tweek to min move as recommended by the GA).The scope stands on a heavy wedge bolted to a concrete pier some 13 inches in diameter 3 feet tall and weighting more than you and me combined. This stands on a concrete platform 4 x 8 feet and 5-8 inches thick set into the ground. The base wasn't made for this purpose but I had to use it for the pier and the roll-off shed.. So, your suggested poor seeing is almost certainly what's amiss here. I did note unusual halos around the guide star/s and have put this down to very high mist/vapour causing a refraction pattern. I hadn't seen this previously. The conditions here are pretty poor these days. When we first moved in, you could see the Milky Way no problem. Now I can't. The sky glow is bad due a nearby power station and street lighting. Local Bortle is Class 5.

Not withstanding, I accept the mount's age and limitations, though it's wear and tear over my 25 years ownership has been pretty minimal. By today's standards, it is primitive. I'm therefore hoping to simply improve on the quality of images I've manged thus far using unguided altaz. If I can only achieve that, I'll be very satisfied. The earlier stuff, though limited, was acceptably good, even at f10. It is very challenging, which I enjoy.

The LX200 Classic does indeed have a PEC training system, though I never got into that. In fact I only brought the scope out of a decade's hibernation last year. Unfortunately, I never had enough time to do the thing any justice. So, I'm hoping to get my feet wet again. It seems PEMpro has a specific facility for Meade Classics, so I need to look into that.

Again, many thanks for your insight, I appreciate it.

Jack

[Jack Thewlis]

Hi Michael,

Yes, it's been breezy of late, though I didn't sense any wind issues that evening nor during this particular run. Having listened to comments so far, I do think bad seeing is the most likely culprit.

I've read a lot of Doc G's stuff and the MUPAG archives and both have helped in work I've done over the years.

Regarding your long fl guiding suggestion. The main scope is operating at f6.3 (1575mm) and the guide scope is 280mm. Do you think this combination is incompatible with good guiding? (discounting the LX200 issues).

Cheers,

Jack

[Jack Thewlis]

An update on my LX200 odyssey. I've adjusted the dec worm contact/tension and trained the RA PEC using Meade's tedious eight minute stare and press routine. Whether it has improved things remains to be seen. In that context, I've uploaded my latest Guide Log at the link below.

During all this, I redid the drift alignment and got it virtually spot on. The GA said it's now somewhere between 0.0 and 0.1 arcminutes in error.

The calibration (of which I ran several between various tweeks of the hardware) confirmed a significant Dec backlash,creating an equally significant orthogonality.error. One of the calibrations showed crazy RA steps and no Dec steps at all. .I believe this was a cable issue, which was followed by a repeat of the earlier one. Not withstanding, I finally settled with a guideing run showing a rediculously impressive 0.2 arc second RMS. Surely this is not possible from a twentyfive year old LX200...? Was I really tracking a hot pixel? I don't thnk so, the star mass trace should confirm it.

Am I getting somewhere on this path?

Guide Log

Cheers,

Jack Thewlis

[Brian Valente]

hi Jack

i think something is unfortunately amiss in your 1 hour guiding session. the 0.22" total RMS shows literally zero corrections, so i find it hard to believe that was guiding on an actual star. 

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[Jack Thewlis]

Hi Brian,

Yes it all looks too good to be true, but I can't yet see where the fallacy is. The 1hr session used the same settings as the shorter guiding tests before it. All earlier checks showed both RA and Dec pulses or just RA pulses. Would the target star mass and SNR graphs not simply flatline if I was tracking a hot pixel? I had the Darks in use but not a bad pixel map, would that be the fallacy factor?

In the last session, starting at 22:04 the exposure was 1s and the traces exhibone or two RA pulses only. At 22:09 I changed exposure to 1.5s and these pulses stopped. Nothing else was changed. I assumed there were no pulses because the 1.5s shifts were below the MinMo settings. At the very end of that session, I ran the GA again and it recommended going to even lower MinMo, which is logical - unless there's a fallacy in play.

I'll run the whole show again at the next opportunity and post more results that will hopefully explain what's amiss.

Cheers,

Jack

On Thursday, April 16, 2020 at 12:09:18 AM UTC+1, Brian Valente wrote:

hi Jack

i think something is unfortunately amiss in your 1 hour guiding session. the 0.22" total RMS shows literally zero corrections, so i find it hard to believe that was guiding on an actual star. 

On Wed, Apr 15, 2020 at 4:04 PM 'Jack Thewlis' via Open PHD Guiding <open-phd...@googlegroups.com> wrote:

An update on my LX200 odyssey. I've adjusted the dec worm contact/tension and trained the RA PEC using Meade's tedious eight minute stare and press routine. Whether it has improved things remains to be seen. In that context, I've uploaded my latest Guide Log at the link below.

During all this, I redid the drift alignment and got it virtually spot on. The GA said it's now somewhere between 0.0 and 0.1 arcminutes in error.

The calibration (of which I ran several between various tweeks of the hardware) confirmed a significant Dec backlash,creating an equally significant orthogonality.error. One of the calibrations showed crazy RA steps and no Dec steps at all. .I believe this was a cable issue, which was followed by a repeat of the earlier one. Not withstanding, I finally settled with a guideing run showing a rediculously impressive 0.2 arc second RMS. Surely this is not possible from a twentyfive year old LX200...? Was I really tracking a hot pixel? I don't thnk so, the star mass trace should confirm it.

Am I getting somewhere on this path?

Guide Log

Cheers,

Jack Thewlis

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[bw_msgboard]

Hi Jack.  You’re not guiding on a real star, it’s just some random clump of non-black pixels on the sensor.  To avoid this, you should use the settings in PHD2 to define what is going to be an acceptable guide star for your system.  You do that here:

 

 

You should use the Star Profile tool to look at typical half-flux-diameter (HFD) values when you know for sure you’re guiding on a reasonable star.  From looking at your log, I’d suggest setting this value to 2.0 and see how things go.  When you’re getting this “perfect guiding”, the HFD values are more like 0.1 to 0.2px.  

 

That will help you avoid this particular problem.  Then you will need to figure out why you aren’t getting more choices with better stars – maybe you’re in a star-poor region of the sky, maybe the guide camera isn’t critically focused, etc.  You should go back to 2-sec exposures for now while you are getting this sorted out.

 

Hope this helps,

Bruce

 

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From: 'Jack Thewlis' via Open PHD Guiding [mailto:open-phd...@googlegroups.com]

Sent: Thursday, April 16, 2020 4:20 AM
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