For MX/ME Users. Expectations re Guiding and T-Point

[PRejto]

I'm still fighting with some strange issues re declination whilst guiding. I've got a thread over at SB that has bogged down a bit but I'm still hopeful about some feedback.

In a nutshell guiding will start off quite well. I wil go perhaps several minutes with very tight guiding. Abruptly I will get excursions in declination that go uncorrected for perhaps a minute or more, then followed by good guiding. Then the problem may pop up again but now on the other side of the Y axis where things just seem to get stuck for a while. I've got the guide camera aligned so RA=X. Aggression is set to "4" which gives a very good result in RA. When I increase aggression guiding is not as good in RA but may improve in declination. I'm unsure if there is a way to increase aggression in just one axis. But, what seems more odd is that decination would even get stuck on the "other" side of "Y." Drift ought to only be in one direction.

I have adjusted the cam stop in declination.
I have excellent polar alignment (Ma=6.1, ME=84.1 or 2 arcsec from refracted pole).
I get same results with ProTrack on or off.
Balance is spot on, and I cannot detect anything loose on the mount or cameras.
PEC on (error is below 1 arcsec)

EDIT: I'm using the Camera Add On in TSX to guide with Direct Guide. Also, the double spike is because I'm guiding through an ONAG in the infra red. I'm assured the guide problem is not due to the double spike but is due to IR passing through a typical APO. As pointed out by Josh below if the problem was the ONAG I would be seeing the problem in RA as well.

Any ideas would be much appreciated!

With ProTrack off, given my polar alignment, how long should I be able to track in Y without significant drift? (guide camera is imaging at 3.12 arcsec- binning 2x2).

Thanks,

Peter

[rogerg]

I haven't seen this kind of problem with my ME.

What's the connection of your guider, are you using Direct Guide? What software are you using, CCDSoft?

I wonder if your guider calibration is incorrect somehow.

Do you see the same behaviour with guiding turned off or is it guiding which is introducing the problem?

I can track for easily over 3 minutes anywhere in the sky with no DEC drift @ bin 1x1. I autoguide for anything over 3 minutes. My autoguiding is quite steady, star snaps back to the centre instantly every time.

I use aggressiveness 10 and Direct Guide with CCDSoft doing the camera/guiding.

Not sure off the top of my head what my guide chip's pixel scale is. The ST8-XME is at ~0.86/pixel @ 1x1.

[Joshua Bunn]

What kind of ADU do you get on your guide star?

The profile of the star in your picture shows 2 spikes, maybe there is some confusion as to which "spike" should be followed? but then i guess this problem would also be on the RA axis.

Ive never tried to see how long i could go without Dec drift, but while doing my PEC log, the guide star doesnt move (except for PE), as i too have excellent PA, and with your PA you would be able to track for a long time (sorry about the subjectivity) without drift. Your issue isn't Dec drift IMO.

As Roger says, i would look at your Dec drift without guiding corrections to try and isolate things, weather its mechanical or a guiding related issue.

What does the Dec guiding graph look like as time goes on? Does it keep oscillating?

Josh

[PRejto]

Hi Roger,
Many thanks for your reply. I'm using Direct Guide in TSX Camera Add On.
I edited my first post to include this information.

I will need to investigate exactly what is happening with guiding turned off. Tonight looks good to do that. Recently I didn't want to disrupt data collection so just threw away frames where things went wrong in guiding. I appreciate your comment about going 3 min unguided without dec drift. Was that with ProTrack off? I have checked calibration numerous times but nothing about this behavior changes.

Thanks,
Peter

[PRejto]

Hi Josh,

I appreciate your comments.

I have long understood the need for good star focus and saturation. The exposures in the photo posted above were 4 seconds. The double spike is caused by infra red passing though my APO and then through the ONAG to the ST-i. As you say, if the double spike were causing this I'd see it also in RA. I don't.

The reason I was asking about declination drift is that a post at SB suggested that maybe my aggression setting was too low and the mount just couldn't keep up with the declination drift. As I mentioned it usually only happens after a few minutes of quite good guiding. The suddeness is surprising when it happens. Perhaps if I could increase aggression in declination only I could control this. But, getting stuck on both sides of "Y" makes little sense unless something mechanical is slipping.

Anyway, tonight I will devote time to seeing what is happening without guiding corrections.

Thanks,
Peter

[rogerg]

No, on. I always have it on except if I forget to turn it on after some sort of testing :lol: :screwy: Tracking is worse with it off, that's for sure.

[jase]

What happens when you calibrate the guider near or exactly on the target you're about the image? If it guides fine after this, it may be that declination compensation is not occurring. Not sure if TheSky does this by default (probably does), but its checkbox in MaximDL. MaximDL simply reads the scope dec to obtain the information. I've not investigated the algorithm it uses to compensate.

[Joshua Bunn]

Good point Jase, TSX does automatically compensate, but its worth a try to recalibrate on the target.

[Peter Ward]

You sure RA=X axis on your graph?

On first inspection, I'd say it looks like it's the Dec data.

[gregbradley]

Is this PMX or PME?

The only experience I have had that is somewhat similar but not the same was guiding PE would suddenly go bad for a few seconds wrecking the image.

SB sent me a new worm and that fixed it. In the process of changing it over it seemed there was a possibility of some gunk from the belt in the pulley. I forget the period for the worm - I think its something like 4 minutes. So if there were some junk on your pulley it would cause a big spike in PE repeating around every 4 minutes. This is what I experienced.

Also with the 3 way switch have you have the dreaded gear slip with a badly unbalanced mount? If you forget to turn it to lock it can slip and grind. The gears seem pretty tough but if you had a heavy scope it potentially could cause damage.

There have been other posts of elusive tracking/guiding problems that ended up being a disconnected lead etc. So its not necessarily stright forward. But there does seem to be a lot of these posts about guiding/tracking issues with SB mounts. They need to raise their QC game or they'll end up like Nikon!!

Greg.

[PRejto]

Hi Peter,

Well, I sure hope I've got this right. I've got my camera oriented exactly as I did collecting PE data with the X axis of the guide camera ccd aligned North. I also used the hand controller to move the RA axis of the scope and watched a star trail move across the X axis of the live view in focus mode.

Of course, if I've got this wrong I'll just be selling all my gear.

Peter

[PRejto]

Hi Greg,

I just have an MX, but thought since the software is the same for both mounts comments from ME users might be helpful to consider.

I'm not ready to blame SB for anything yet. My inexperience probably is to blame!

Thanks,
Peter

[SpaceNoob]

I have been having similar guiding issues with the Fw8g-STT. 10min unguided subs ok, then start guiding and after 5-15 minutes it's like the guider gets a mind of its own in one axis, with the graph error growing exponentially. The mount seems completely fine but I suspect it's software related with the guider or how theskyx handles relays. Sometimes I find during calibration, both x and y relay tests go the same direction lol, after trying again it works.... Go figure.

P.s, both relay or direct guide has similar issues

[Peter Ward]

Sorry, still not convinced.

While recording your PEC data, give the dive a blip in RA with the HC...or even switch the mount off....

I always prefer physical proof over software :)

[PRejto]

Last night proved a bit frustrating. It was windy and the seeing wasn't very steady so hardly ideal for studying guiding. I spent a lot of time rebalancing the mount - especially in declinaton - and did discover more bias than I originally saw. After that was corrected I did a 50 star T-Point recalibration and discovered that MA was somehow different than a previous measurement and is now at -57.9 whilst MA remained unchanged and is quite good at 63.2 (within .3 tics of refracted pole).

Posted is a plot of an 8 min unguided run, as well as two runs at aggression "5" and "4."

I did not see the issue that started this thread, but do see some large sudden deviations perhaps due to the wind. But I'm not sure. Are those sudden spikes normal?

One person at SB (Alph) has been giving me some information about the calibration data. It appears that one can make adjustments to the velocity (Pix/sec) after calibration. This would allow one to make individual adjustments to the aggressiveness of corrections in certain directions. I bumped up the Y corrections form .60 to .75. I thought perhaps the result was a bit better. When I decreased the values from .60 to .45 it was clearly worse. But by then it was quite windy and getting towards 1:30am. Enough.

Anybody see anything in these? To me it looks like I might be better off not guiding (if I wait one minute before starting), but maybe I'm missing something such as trying even lower aggression settings.

Peter

[Joshua Bunn]

Well, from your first graph it appears PEC is working on your "X err pix" so your camera is oriented with the x axis aligned with RA. Also, there appears to be some drift in Dec maybe due to slight polar misalignment.

There however is no evidence of the swings from positive to negative pixel errors in your dec graph that you saw when guiding. this probably indicates its not a mechanical issue and that guiding settings are the cause of you erratic Dec graphs you have seen. This is of course looking at the first graph.

Its a little hard to tell if those spikes in the second and 3rd graphs are significant because there is no scale. However, they don't look smooth enough to me.

Sounds like playing with those pix/sec settings after calibration may help, where are these settings?

Josh

[Paul Haese]

Not having dealt with my PMX yet this is how I would approach the problem.

First do an unguided run and see how things plot out. Without any wind.

Next use something like MaximDL or PHD to guide the mount with. Don't use the SB software at all.

The reasons you want to do this are as follows:

1. You want to establish whether this is a software or hardware problem.
If it is hardware it will show up in unguided mode. If everything looks right unguided then you can eliminate hardware. Spikes etc or bad PE will show up unguided.

2. You then want to establish if it is software; if this is some problem with the SB direct guide or the guiding part of the program. Using standard settings in MaximDL via normal calibration at one part of the sky (preferably near the zenith) will tell you want it going on. Try also guiding with and without a connection directly to the mount.

Like I said at the conference Pete. You need to be methodical about eliminating one problem over another. This is most likely several issues going on here.

The solution to the problem will present itself. PM me for my phone number if you like and we can talk more.

[gregbradley]

I am still using CCDsoft rather than the Sky X camera add on. It is a stable and mature software that is very predictable and reliable.

You could also try that out in case its a Sky X issue.

Greg.

[PRejto]

Thanks Josh, Paul, and Greg!

All great advice and much appreciated.

Josh, I think the scale is actually there on the log graphs. I'm pretty sure each tic mark = .2 pix. For some reason the graph displays differently when there are no guiding corrections.

Paul and Greg, Now that I know that I can graph CCDSoft logs in TSX I think I will use CCDSoft and compare results to see if it is software related.

I appreciate your offer to help Paul. If I get totally stuck sorting this out I may need to call you.

Now, a night with no wind, please!!!

Peter

[Terry B]

I don't have a PMX but have seen similar problems with Dec guiding with my tak mount.
If I turn dec guiding off and only guide on RA there will be a very slow dridt one way depending on how good the polar alignment is. I can go for ~20 mins with little drift evident. Superimposed on the drift will be almost random movements both directions due to seeing changes. If the Dec guiding is set too sensitive the guider will then bump the mount 1 direction. Sometimes it will overshoot and then try to bump it back. This will take time though due to the backlash in the dec system requiring more then 1 bump of the guider to move it back. This can set up the pattern you see.
I have also had occasions when a cosmic ray hit or interference has occurred on the guider and the mount has reacted wildly to this pushing the mount a long way and then it overshoots correcting it.
I mostly turn dec guiding off to overcome this problem.
Cheers

Terry

[PRejto]

Thanks Terry. That's very helpful input! I'd better tighten up my polar alignment. I'm finding that azi is quite difficult to nail when one is close. On the MX often I will move the required tics (from T-Point) and the mount actually hasn't moved. I might need to run 50 points in T-Point just to figure that out and then start over. I am able to chart moves photographically in altitude but when I tried the same trick in azi it failed big time. I'm not quite sure I understand why. Can anyone here provide a method for verifying say a 1 arcmin move in azi photographically?

Thanks,
Peter

[Joshua Bunn]

I would have thought do the same as what you did for Alt, but for Azi instead, this is probably what you tried?
A move in Azi would result in the scope moving in RA Depending on where in the sky you were pointing, if im not mistaken. I think this would apply if your scope was pointing at the meridian. So take your image then image link it. Jog your mount 1 arcmin in RA, then move your Azi knob the required amount to get back to the plate solve.
Does this sound right???

Josh

[PRejto]

Hi Josh,

I posted this very question at SB and received quite a response. You might want to read: http://www.bisque.com/sc/forums/t/19832.aspx

Peter

[Joshua Bunn]

Thanks Peter, Quite a response.

[PRejto]

Just a bit of an update.

Got under my deck yesterday and discovered to my horror that the bolts holding my pier down were only finger tight! Heat/cold cycles I guess?

So, spent most of last night just redoing T-Pointing and finally dervied a new model that looks pretty good. RMS=8.5 (200 points), MA= 23.5, and ME = 15 (from refracted pole). I managed to do this in two runs. The first was about 50 points that I took care to make sure included the extremes of what is visible from my location. I had never previously taken points that low down but I'm assured by Patrick Wallace that the MA term requires these for more accuracy. I then moved the mount according to the T-Point super model recommendations but I confirmed both moves photographically. Again, from Patrick Wallace I learned how to do this for MA: cos x altitude angle (on meridian pointing North) x arcsec move indicated from T-Point PA = actual move to make. Thus, if T-Point says move 1 arcmin in MA and the scope is pointing 40 degrees dec then: cos(40 degrees) x 1 arcmin = .766 arcmin (the amount you move the scope photographically). It will work anywhere in the sky but on the meridian it's easier because the declination control will move the scope in a way where it is easiest to measure the actual move (in a vertical line if camera has dec=Y).
I used my ST-i in focus mode and the jog controlls to do this.

After making the moves I ran a 200 point model and was pretty happy to see how close it ended up. For the 200 point model I started out by taking about 10 points manually again selecting the extreme points in the sky visible, but for the remainder of the 190 points I confined the run to about 35 degrees and higher.

Should I worry about the MA term, or is it close enough?

Peter

[Joshua Bunn]

Well thats good news Peter.



Personally i think your close enough.

Getting to the perfect zero in Alt and Azi may not be the best thing. You may have seen this over at SB. If you type in "Polax" to your command line in tpoint and execute, you will get ideal Azi ans Alt settings to minimize certain undesirable points.

hers mine:

Polar axis settings: ME MA
+82 +12 current setting
+84 +0 refracted pole
+48 +0 minimize field rotation
+76 +0 minimize unguided declination drift
+77 +36 minimize unguided total drift


The polar axis is currently 82 arcsec above and 12 arcsec
to the right of the true pole.


To reach the refracted pole, raise the polar axis by
2 arcsec and rotate the mount anticlockwise by 15 arcsec.


To minimize field rotation, lower the polar axis by
34 arcsec and rotate the mount anticlockwise by 15 arcsec.


To minimize unguided declination drift, lower the polar axis by
7 arcsec and rotate the mount anticlockwise by 14 arcsec.


To minimize unguided total drift, lower the polar axis by
6 arcsec and rotate the mount clockwise by 29 arcsec.


Quite a neat feature


Josh

[PRejto]

Josh,

Many thanks for that tip. I wasn't aware of it!!

Peter

[PRejto]

It looks like I perhaps should go one more step. It seems MA ought to be at least "0" or on the positive side rather than -23.

If I understand things correctly I can do this by making the recommended changes and then synching back into a "portable mount." I think if I did 50 points I might be able to save my 200 point model. Have I got that right?

Polar axis settings:

ME MA

+67 -23 current setting
+88 +0 refracted pole
+48 +0 minimize field rotation
+82 -0 minimize unguided declination drift
+82 +20 minimize unguided total drift


The polar axis is currently 67 arcsec above and 23 arcsec
to the left of the true pole.


To reach the refracted pole, raise the polar axis by
21 arcsec and rotate the mount clockwise by 28 arcsec.

To minimize field rotation, lower the polar axis by
19 arcsec and rotate the mount clockwise by 28 arcsec.

To minimize unguided declination drift, raise the polar axis by
15 arcsec and rotate the mount clockwise by 28 arcsec.

To minimize unguided total drift, raise the polar axis by
15 arcsec and rotate the mount clockwise by 53 arcsec.

Peter

[Joshua Bunn]

Yes, you need to use the portable recalibration option to save your large Tpoint model. And, i would agree that it would be better to be on the +ve side rather than -ve of the refracted pole in MA.

Josh

[PRejto]

Josh,
I've got another question for you about the recalibrating into a portable mount option. I've remembered doing this in the past and not being too happy with the result. Let's say you do a lot of points to recalibrate back. At the end, though, the RMS is certainly not even close to what it was with the original super model, and, you cannot run the super model again (unless I'm doing something wrong to start with). In fact, the PA reports are quite different between a non-super T-Point run and Super model T-Point run, so for example if the main purpose was to re-establish ME and MA you seem to end up with numbers that cannot be compared to the numbers you were trying to modify. I've noticed that MA doesn't change so much between a super/non-super PA report, but that ME varies quite a lot. Is there a way out of ths situation or is the only answer to start over from scratch with a new model?

I'm imagining that somehow you could reverse the super model and continue to add points to the original model, and then run the super model again. I suppose that just isn't possible.
Peter

[Joshua Bunn]

You cant do this. Once the supermodel/model is finished you cant add points to it.

I hear what your saying about the RMS values not being as good. Is that the only issue, is it just that the RMS values are not as good or is the mount not pointing how you want it to? Ive wondered about this too and posted about it on the Sb forum some time ago. I was asured my mount was using the larger 2,3,4,500+ original model i initially made and not the short 20 point model. I guess the not so good RMS results you see for the recalibration are just for reestablishing the terms for the large model which is doing the work. In short, all is good and the larger model is working as it should.

I wouldn't use the 20 point recalibration data to gauge your PA, this needs to be done using a 50 point model (see the last post on this (http://www.bisque.com/sc/forums/p/17832/74924.aspx#74924) page). But if you do end up doing another larger tpoint model, you will get a better approximation of the PA and can make the recommended adjustments with more confidence as there are more samples to work from.

After you have done the 20 point recalibration, does the scope point how you want it to?

Does this answer your question?

Josh

[Bassnut]

You guys sound like you know what yr talking about, so here's a question.

The super model corrects on the fly, so does PEC, looks like potential conflict to me. What gets priority?, can't have both correcting at the same time, or do they talk to each other and behave?.

[Joshua Bunn]

Well, they are suppose to work together, I use them together and it works for me. What do others think?

here (http://www.bisque.com/sc/forums/p/12609/47565.aspx#47565) is a post that describes it.


Josh

[Bassnut]

Access to this Resource is Denied

mmm, must be secret, thought as much.

[Joshua Bunn]

Yeah, you need to be registered.

here is a snippet, hope im not violating anything:

This is the best link for an explanation as to what PrecisionPEC is and does versus Protrack,
http://www.bisque.com/sc/forums/p/9710/35396.aspx#35396
From the link the following is per Patrick Wallace and I quote.
"ProTrack and PrecisionPEC are complementary, each specializing in different parts of the same job.
PrecisionPEC eliminates the all-important high-frequency irregularities in tracking rate that are caused by the tiny residual imperfections in the RA worm drive. Protrack applies the TPoint all-sky pointing model to mop up the much slower drifts caused by such things as flexure.
Although Protrack could be made to do at least part of what PrecisionPEC does, it would require an inconveniently dense TPoint mapping run, and the diagnostic displays and tools offered by PrecisionPEC would be lacking."
There are also 2 additional links to provide examples showing how Protrack improves un-guided tracking by eliminating errors like polar miss alignment, refraction, and flexure. One is here from a customer,
http://www.bisque.com/sc/forums/p/8034/28616.aspx#28616

It should be noted that by not compensating for refraction and or tube flexure you can't expect pixel level tracking for extended periods without guiding. Extended being in many cases longer then about 1 minute with any appreciable focal length. Often times the sagging OTA will cause several arcseconds of error in only a few minutes.

Another more drastic example of what Protrack can do was posted here by me. By showing images before and after Protrack was enabled and after introducing a 30 arcminute polar alignment error to demonstrate, actually 28.5 arcminutes off the pole before and after ProTrack using 67 points and Super Model.

http://www.bisque.com/sc/forums/p/12309/46280.aspx#46280
By employing both of these even while guiding you will compliment the overall tracking performance.
And I almost forgot What is Protrack??
http://www.bisque.com/help/paramountme/paramount_me.htm#what_is_protrack.h tm

[Bassnut]

Excellent, thanks for that Joshua.

[PRejto]

Hi Josh,

you have been busy fielding all sorts of questions!!

Thanks for the clarificationn. I'm not really so concerned with pointing, but if the aim is to improve PA perhaps doing a recalibration (with 50 points) will work just fine. But, the real issue for me in doing that is that you end up with recommendations that cannot be super-modeled. Given that the original data was super-modeled, and one is trying to refine those numbers, after a recalibration you end up with numbers that really don't tell you if your adjutment moves actually helped. Am I making any sense here? So, it seems that if you want to compare super model numbers before with super model numbers after the only way is to start a new model from scratch.

The only way I can imagine out of this situation might be to save the original super model of many hundreds of points. Start over with a 50 point run and run the super model. That would tell you if the adjustment was correct and PA actually better. If so, discard that new model model and re-load the original super model and do a 50 point recalibration into that model. The PA report wouldn't necessarily show an improvement but you would know that it was actually better. Can you think of another way?:)

Peter

[gregbradley]

I don't quite understand this thread. I am not sure why you would need to know about converting arc minute errors into how much you adjust your mounts PA? Super Model or PA report does that automatically and tellls you how many ticks to adjust. Is this for those whose mount is not an SB so they have a way of knowing how much they need to adjust their mount?

I also have a question as I have only just started using ProTrack to help with guiding.

I did a full new callibration run the other night. I adjusted the PA just the small amount it said to. I ran another large model this time 330 points. It took about 3 hours to do (perhaps my 10 second exposure length at 3x3 binning is too long).

It came up with the same adjustments needed to the dec and RA axes but also said they were good enough.

I did a 5 minute unguided exposure with Protrack turned on and it had stars duplicated 3 times like a correction was applied at 3 points.

But then when I did my normal PEC autoguided image there was a noticeable improvement in the roundness of the already quite good stars. Everything was tighter and the final image will show better resolution and sharpness because of it.

Do you find you can do a 5 minute sub with sharp round stars with just ProTrack?

Martin Pugh at AAIC said you had to experiment and see what combination works, Protrack on PEC on, PEC off Protrack on, Protrack on PEC on. He said for his mount Protrack with PEC gave a worse result. My limited test here seems to show an improvement (although I have not done a 15minute sub with PEC on and Protrack off yet). Per that thread they are complementary and work on different aspects off error. Its nice to have a tool that sophisticated to take the tracking to the next level.

As far as adding to an existing model when you try to do an automated callibration tpoint run it gives you several options. Can't you just use the sync function or short mapping run if something has been adjusted manually to bring the model back to reflect the current state of the mount after physical adjustments?

Greg.

ps. RMS f 8.5 is very low. Mine is 21.1 after 330 points at 3 metre focal length.

[PRejto]

Hi Greg,

I cannot answer all of your questions, but I can attempt it with a few.

1. The initial point of this thread is probably lost somewhat in the current discussion, though it is all ultimately about getting better guiding in the end. When I discovered that the bolts on my pier to the concrete base were loose I needed to start my model over and that has led to the current discussion.

2. I think the problem you experienced is exactly the main point under discussion. That is, you spend many hours doing a long T-Point run, apply the super model and then discover that the mount requires 1 or more smallish physical adjustments. Yes, our paramounts have tics to make this easier, but as you can see in your own application, moving the mount a small amount seems not to have resulted in a change in your new T-Point model. Small moves may actually not really move the mount no matter what the tics say! So, many of us verify the change photographically so that we know without question that very small changes have actually taken place. There was a recent statement at SB about this. Namely that if you make a physical move, and use the same points to compare the before and after results, that the change WILL be refected in the PA report (as long as there are enough points collected). Therefore I would hazzard a guess that when you thought you had moved the mount a little bit it actually didn't change.

I'm sorry if I'm being pedantic and have not understood your message!!!!

3. My issue is that you and I may run a very lengthy T-Point that we then super model, correct? If you look at the PA reports before and after running the super model they are frequently quite different values, especially the ME term (elevation). The point I was making in my last post is that if you have a large T-Point model that you wish to save and continue to use, but you need to refine the PA as well, is can this be done?. The answer is yes...you can make the adjustments recommended by T-Point (probably best to photographically confirm those adjustments) and then pick the option to "recalibrate into a portable mount." That option will supposedly figure out the new ME and MA terms but preserve all the other terms in the original super model. This sounds great until you actually try it. I'm not saying it doesn't work. I'm sure that it does. However, what you see (after say doing a 50 point recalibration) is not the original super model refined. What you see are just the non-super model results of the 50 point run. The super model runs behind the scene (I guess) and you still get great results. However, if the reason that you recalibrated was to check on the final results of the recalibration by reading the new PA report the numbers reported for polar alignment cannot be directly compared to the numbers in the initial super model report. So, it appears that in the end (if you recalibrate) you have to take it on faith that the numbers for PA actually improved. The only way out of this situation would be to do a full T-Point run starting from scratch every time you make physical adjustment to the mount because this would allow one to make direct comparisons between each run as to PA accuracy.

I'm sure if I've got this wrong somebody will jump in. I'm actually hoping there is a different answer! And I hope I have not confused this even more!! It reflects my current understanding of this.

PS. I would think that your RMS value might be a bit better. Are you running the super model? The reason I ask is that prior to running the super model (and accepting the result) my RMS was around 60. After super model it went to 8.5 If you have been skipping the super model (and I kind of doubt you are) be sure to look at the before and after values in the polar alignment report. I did my last run at ca 1750 mm, but I've got no mirrors to move at all.

PSS. My memory of what Martin said was just a tad different. I'm not remembering him making any comments about PEC being turned of to use ProTrack. I think ProTrack requires PEC to be working. I think he said to experiment with guiding having ProTrack on or off. I know of several people that have more trouble with guiding with ProTrack on. I cannot comment for myself about this because I have made a decision a while back to "uncomplicate" things re guiding by doing my experiments with Protrack off (but PEC on for sure).

Peter

[Joshua Bunn]

If your aim is to improve PA, and you want to preserve your 200 point model, yo will need to save / export your model, i think as a dat file, then start a new pointing run which will clear everything (it wont delete your save data). Run your 50 modeling points, make the recomended adjustments until your happy with it. Its not an iterative approach but you may want to run 2 maybe 3 runs. Make sure you get pointing samples low down.

Once your happy with your PA, clear the model then import your saved 200 point model and super model it. Now you need to do a recalibration run using the portable mount option. Choose about 20 points from the SCP area up to Dec 0, over to the west and to the east, and scater some down near the horizon. once the points are captured, press finish, no super modeling required. Your Done, and although the scatter plot and RMS values may not look like or as good as your 200 point data, the mount will be using your 200 point data.



Thats it, although 50 points for recalibration is not necessary, 20 is fine. 6 is what the manual says i think, but 20 has been mentioned on the forum.

Josh.

[Joshua Bunn]

I would say you can significantly reduce this time. Personally i use 9x9 binning (STL11000) with about 2 sec exposure for about 240 odd points an hr. You could easily do this with you gear Greg with bigger aperture and a more sensitive camera. maybe you need to tweek your image link parameters.




Well it seams Protrack, autoguiding and PEC are working well together for you Greg. With protrack on and i thing PEC was on, ive done 15 min unguided at 2.5m FL with round stars. This was after using a 550 - 600 point model, not a re-calibrated model. the original models have given me more success than recalibration runs in terms of Protrack unguided tracking. Pointing is spot on.



When you start up one night and you find the mount points, say, 1/2 to 1 FOV away from where it says its pointing, then you can sync back into the existing model by image linking the photograph then synching the mount to it. that's fine. This wont work if you make ANY adjustments to the mount weather it be PA or loosening or changing the scope / dovetail position on the mount. In this case you need to choose the recalibrate for portable telescope and recalibration permanently mounted telescope respectively. You select the appropriate option then do your 20 or so point recalibration run as described in the manual and this thread. It doesn't need to be super modeled.

Josh

PS, I havent yet read Peters reply to you Greg, so sorry Peter if ive repeated what you have said.

[PRejto]

Josh,

Thanks for your answer about how to save my existing model. You confirmed what I suspected and I appreciate that very much!

Peter

[Joshua Bunn]

As far as my understanding of Tpoint goes Peter, I think you understand it well. I will say that after you have donr the 200 point tpoint run, this should give you an excelent representation of your PA and from there, any adjustments made to the PA should be made in confidence. Apart from that, as you say above, if you make an adjustment to your PA, then do a full 50 point polar alignment tpoint run to verify before and after PA reports with supermodel. 50 points is all you need realy. DOnt read off the recalibration PA report.

In reallity, we have seen that there is no perfect PA position and that aiming directly at the refracted pole may not be the best option. So in practice, when the PA report says its excelent an no further adjustments are needed, then you OK.

Do you think your Dec drift was because of the loose pier mounting bolts? Have hou tried another guiding run with the tight bolts?

Josh
Josh

[PRejto]

I sure hope so! Especially given that my original PA report was evidently in error given the loose bolts. But, I've yet had no opportunity to test properly. I'm also hopeful that some of the unexplained spikes might have been due to wind impacting on the mount. I think I will make one more move of the mount and hopefully be done with PA for a while.

Thanks for all,

Peter

[gregbradley]

Wind definitely causes PE spikes. You can watch the guiding, hear the gusts and see the errors spike up straight afterwards. Also depends on the type of scope. A closed tube CDK would be like a sailboat. It would have no hope in the wind. Even mild winds will affect those large closed tubes. Not ideal as a design but probably easy to build.

Hopefully its simply loose bolts. Kind of humorous in a way. Searching for obscure software/firmware glitches and hitech explanations to do with T-point models, backlash settings and its just loose bolts!

Kind of matches my experience though. Often problems are simple ones and often in your face type obvious ones rather than abstruse hidden in software issues.

Greg.

[PRejto]

No kidding!! I kind of feel like an idiot. Tonight looks to be clear so the verdict awaits!

Peter

[Joshua Bunn]

No problem Peter, it can happen to anyone. We wouldnt give advice if we didnt want to.

[frolinmod]

Imagine those poor Bisque boys sweating beads in frustration trying to figure this one (mount problem? software problem?) and it turns out to be wind gusts? Oops. :D

[PRejto]

Yes, it must be frustrating. I agree!

Unfortunately, though, tightenting down the mount, and running brand new T-Point models, have produced strange unguided results which I simply do not understand.

The resuls shown below were taken after midnight in good seeing at dec=+3, HA=0, close to the meridian with X=RA. Analysis of the 15+ min tracking log (this was with PEC on and Protrack off but unguided tracking) shows corrected PEC of .7 arcsec. But the graph looks pretty terrible! Almost immediately there is a large rise of nearly 6 arcsec (I imaged at 1.56 arcsec/pix) followed by several bumps. Only around 850 sec-1,000 sec does the tracking drift down to the X axis. And there is steady drift in Y as well. More than I believe should be seen at HA=0 where any declination drift should be quite minimal. To me it looks like both axis are drifting. But how could that be if polar alignment is supposedly so good? My T-Point PA report (based on nearly 200 points) is -23 arcsec azi and -15 in ME from refracted pole.

I asked the question at SB as to whether not seeing the whole sky could cause an error in PA using T-Point. I only see from overhead to the West and not very low to South and North. The answer I received was that it ought not to make a difference, but that T-Point is a statistical model and more points are better. I guess that leaves the door open.

To say I am frustrated is a gross understatement.

Peter

[frolinmod]

Please turn ProTrack off, pretend you've never even heard of Tpoint and ignore its polar alignment suggestions, spend some time drift aligning your mount, then repeat your test a few more times. Any difference?

[PRejto]

That will certainly be my next step! I was thinking about using Pempro to do this which I believe is a drift align using a camera. I've never done one before so I'm sure I will mess it up before I get it!

BTW, Protrack was off for the guiding graph posted above. Does it look right to you?

Thanks,

Peter

[Joshua Bunn]

Ill second the suggestion for a ccd drift align polar alignment check. The results will be interesting to see.

[PRejto]

Josh,

I've been thinking that I might try one thing first that shouldn't take too long. If the problem is that my pointing samples are skewed so much to the West, I wonder what result I would get if I confined my samples so there was no bias in any direction?

You can see my horizon line compared to what I propose. It wouldn't take too long to run this and then compare the polar reports for the two models. If they are the same or very close then I will drift align, but if not hopefully the new model would be better.

Peter

[Joshua Bunn]

I appreciate what your saying, but i think samples low on the horizon are a significant contributor to the accuracy of the model. Maybe a question for Patrick W...?

Having said that, I would be interested in the results.

Josh

[PRejto]

Well, now that you ask.... I did ask him in the thread at SB. He did say to collect points very low down to the West. So I've done that in my current model considerably more than I ever have before. I have a terrific pointing model but I think my PA is further off than ever before no matter what the PA report indicates. My guess is that there are no "compensating" points low in the East and something is going off. I specifically asked Patrick if my particular horizon could be a problem. He didn't think so but did say more points are better statistically. I think there is a possibility that T-Point is not working properly when there is 50% of a horizon missing. Anyway I'm going to run the experient as soon as the weather breaks. I'm really curious.

Peter

[cfranks]

I was going to recommend Pempro! My last PA was using Pempro just once. I then did a ~ 180 point TPoint and got a RMS (on my MX) of 4.3as. I eventually messed it all up by removing the mount for maintenance but plan to do it again tonight, the moon's not conducive even for NB, being just where I don't want it!

Charles

[PRejto]

So, Charles, you used Pempro to align the MX and your T-Point was just for pointing? Or, did you further adjust the mount based on T-Point's PA report? I guess I'm curious as to how close T-Point said you were after running Pempro first. Of course you probably are not so restricted in viewing as I am!

Peter

[gregbradley]

I recently purchased Pempro on the basis from a few threads here that it gives superior results. There was a long thread recently about PEC in Sky X and PMX mount being out of whack.

My PEC on both PME and PMX improve the stars in my images. But I am looking for that extra tweak as per Ron Wodaski's talk at AAIC about software being the cheapest component of your system. And to tweak your existing system to get the biggest gain for buck compared to constantly upgrading gear.

For the record I recently did a 330 poin t-point model and turned Protrack on. I noticed sharper stars and tighter guiding with Protrack and PEC on with my PME.

Greg.

[PRejto]

Yes, and wouldn't you guess that I started that thread on PEC at SB. Maybe I should get a prize for "longest threads or something" since I obviously cannot do any imaging!!! You know there was a PEC bug in TSX just in the Southern Hemisphere that is now fixed, but it took ages for SB to recognise what so many users here were reporting. Anyway, I'm still using the model for PEC I got using Pempro. I'm sure that T-Point normally works fine for most people in terms of Polar Alignment. I think my horizon is messing with the logic of that program because I now believe I have never been properly aligned no matter what T-Point has said. It has caused me a lot of grief for too long, but when a person is just getting started with imaging it takes a bit of time before one has the confidence to say "I don't think this is my fault."

Peter

[cfranks]

After the alignment with Pempro, I ran the 180 ish image TPoint and the RMS was 4.3. The Model said 'excellent' for both axis and therefore I didn't touch anything. I'm currently re-doing the exercise as I recently removed the mount from the pier for maintenance and would have lost the fine adjustment.

Charles

[kimrichards]

Hi Peter et al,

I read in your last post that you use the PEC from PemPro and not from SkyX.

My uncorrected PE is only about +/- 0.8 arc secs so smaller than the seeing noise. Although the recorded error curve looks good, when it is applied the PE sometimes stays about the same or more often gets worse, it never improves. I had put this down to seeing noise and some inventive interpolation by the SkyX and as I usually guide I just left PEC off.

However, I have recently tried some unguided runs and have found that ProTrack definitely makes things worse, presumably because no PEC is being applied, so I now question my previous assumption and looking at the PEC curves I am again questioning the phase of the correction.

So has anyone actually made a good PEC using SkyX for an MX mount in the Southern Hemisphere. The software fix earlier this year corrected the rotation error for the SH but I am wondering if it fixed the phase issues?

Regards

Kim

[Logieberra]

Kim, as they say, are you measuring PE with the latest build? A few months back I tried to measure it in Windows, after the apparent 'southern fix', but couldn't get it working (n.b. don't rule out user error, I often get this stuff wrong) so I resorted to Mac, which did work for me. MX corrected under 1 arcsec p to p.

Also, there is talk of a new 'Automated PEC Routine', expected in the next build. It may already be here? I sure like the sound of that. I do love TheSkyX, but there is no denying that the PEC calibration routine in Pempro is (was?) far simpler. Let's see how Auto PEC fares :)

[PRejto]

Thanks Charles! It's good to know that both methods did agree in your case. My horizon is so odd that I suspect they will not agree. I just need a clear night.
Peter



Hi Kim,

Well, I have not actually tried TSX for PEC since I have such a good result from Pempro. I assume it works now but someone else will need to chime in. It is interesting that seeing seems to influence the amount of correction that either program reports from night to night. If seeing is average both will say my PEC is under 1 arcsec. But on an exceptional night a 15 minute test said my PEC was .2 arcsec. Perhaps that is unbelievable...but, from night to night the reports do vary.

I've always understood that to get good unguided tracking with Protrack one needed PEC, but I'm sure that is only because without it there would be too much error. On the other hand if your uncorrected error is so low it doesn't logically follow that Protrack would require PEC to be turned on. It just shouldn't need it. Of course I am speculating on this without proof. But say you had some sort of mount without any PE. It wouldn't stand to reason that Protrack would require PEC. Perhaps your T-Point model isn't as good as you think? Also, you might try waiting for 2-3 min before starting imaging after a slew. Some have reported that it improves things. Not at all sure why that should be so but might be worth trying.

Peter

[PRejto]

The long story is here but you need to be registered at SB to read:
http://www.bisque.com/sc/forums/p/19914/86165.aspx#86165

Briefly, I ran a new super model where I restricted points to be eqidistant from the meridian E and West to minimize any potential bias due to my inability to see very far East. The super model differed from the the all sky super model substantially in altitude indicating that I should raise the mount 1.2 tics. This is 1 arc min different from the all sky super model of some 200 points. There was essentially no diffeence in the MA recommendation comparing the reports.

Before doing anything to the mount I ran Pempro. Pempro showed perfect alignment over 15 min of tracking in MA. ME, however, was off by .7 arc min also ndicating that I should raise the mount. I did in several moves and now have substantially better unguided correction than I've ever had since owning my MX.

Unfortnately I have very strange excursons in RA that may or may not be PE. Analysis of one guiding log says my PE = .7 arcsec (corrected). Then after I adjusted ME, the next log said my PE error was 1.8 arcsec. Maybe it's seeing or that I collected data at 1.56 arcsec, or that PEC isn't working as well as I thought. I attach the two guiding graphs for comparison. Obviously drift in both axis has improved quite a lot (Protrack was off!), but the huge excursions in RA don't make sense to me with PEC on (and previously verified numerous times to be working). Any ideas?

I ran out of time and enery at 2 am so this must wait. But, I'm happy to finally understand where T-Point has led me astray.

Peter

[gregbradley]

Sounds like PEC is making things worse. Is it the same result with PEC turned off? If PEC curve is upside down it worsens tracking.

There was a long thread recently about PEC in PMX and it was not working properly and it seemed to boil down to it was out of sync with the mount somehow. Perhaps that is what you are colliding with.

I got Pempro myself last week with the intent of replacing my SB PEC curves with a Pempro generated one. As I recall someone else did this several months ago and got improved results.

Its quite possible SB PEC is bugged or bugged for southern hemisphere.

Try a straight no PEC, Protrack off, 10 minute exposure and post the image. Then another with PEC on of the same scene.

Greg.

[Joshua Bunn]

Are you referring to Peter's mount or generally speaking? Im sure there are lots of users who use these 3 in combo without issues, me included.

Peter, I would strip back to the essentials here and just measure the PE without protrack and with the best polar alignment you can get with your choice of software or try the ccd drift method with the continuous exposure and getting the lines to run back on themselves. We can precede from there with confidence that there is no software influences.

Josh

[gregbradley]

That's right Josh. There was a thread posted here a little while ago with Thomas Bisque talking about this point.

PEC corrects for high frequency gear/worm errors and Protrack corrects for slower errors like flexure and refraction.

It seems to me its like the SBIG differential autoguiding where you have rapid corrections for the gear errors and then a slower one for flexure - same thing.

I definitely see a gain using a 330 point Protrack model in tightening up images with PEC on. Martin Pugh though mentioned in his talk to test the combos and for him he found Protrack on worsened. YMMV.

Greg.

[Bassnut]

I put that wrong. Anyway, I suspect I'm wrong altogether so that post is gone.

[PRejto]

I thought I'd best update the post earlier where I compared the two T-Point models and came to the conclusion that one of the models was incorrect, then used Pempro to drift align and finally got better polar adjustment, etc. Anyway, that post at SB generated several large responses from Patrick Wallace and he comes to a very different conclusion than I did. I certainly bow to the master here and feel well in over my head. Patrick has said that using Pempro to drift align just hides the flexure that is there. Yes, I might have a better result but the problem does remain.

Edit: I have deleted most of what I wrote because (again) Patrick has corrected my interpretation of what he wrote. He concludes that I do not have abnormal flexure and there is nothing to fix. The question seems to be about why Protrack doesn't give me the results I want, and why I have trouble guiding. These probably have little to do with polar alignment so I might have been looking in the wrong place for answers.

To be continued...

Peter

PS. Last night I redid my PEC with Pempro. From 2.4 PTP to .9PTP. Hopefully I can refine this even more. Seeing wasn't too great to be collecting data at .63 arcsec. The night before I tried using TSX to correct PEC. I couldn't get it to give a correction but I may have been too hasty and seeing wasn't as good as last night and my data was at 1.5 arcsec. Too many variables to draw any conclusion about TSX.

[Joshua Bunn]

Hi Peter,

Haha, yeah, the original reason for this thread. thats a good point that Patrick makes - one that i overlooked. In that case, do you know if its the scope or mount? do you have another smaller scope you can mount and do some tests with that?

Josh

[Joshua Bunn]

hang in there mate - its character building :P. You will reap the rewards after this. Ive been trying to sort out some issues to, hopefully the fix i have in plan will fix it.

Josh

[PRejto]

Hi Josh,

Patrick added more clarification worth reading. Seems I don't have a declination problem to fix. The question seems to be about my inability to guide properly and why Protrack doesn't give me the results I want and others seem to get.

I think I will leave my Polar Axis where it is, run one more large model (and ignore the PA report) and try more experiments with Protrack on.

Peter

[Joshua Bunn]

Yes, i read that. Sounds like a plan, then see what protrack does for your tracking with out guiding. did you find out if you PEC is good?

[Logieberra]

Peter, to eliminate a few variables, have you considered going portable for a night? Rip your gear off your home/permanent setup, head out to a dark site with good seeing and appropriate footing and do a large all sky calibration run with a few hundred points from there. It would certainly rule out any issues with your home setup.

Not sure if you have a solid MX tripod, I know that Phil sold his recently. You're welcome to borrow my modified AP portable pier to test. It's built like a tank.

[PRejto]

Hi Logan,

Thanks for the offer. I've got a good tripod for the MX and just might do that. I'd need to figure out a power source first, then where and when. Lots of work but probably worth the effort!

Peter