For MX/ME Users. Expectations re Guiding and T-Point
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).
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.
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?
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.
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.
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
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.
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.
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!!
On first inspection, I'd say it looks like it's the Dec data.
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.
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.
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!
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
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
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....
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.
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?
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.
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.
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
Tracking is worse with it off, that's for sure.
