G11 guiding help needed

[Exfso]

My G11 decided to have a guiding hissy fit at Snake Valley and as a result I got zero imaging done. So I have totally stripped the mount cleaned all the bearings, worm and gears and re lubed. Set up both worms and gear with feeler gauges and still it is carrying on. RA looks fine, but Dec is the pits. I have confirmed I have slight movement between worm and gear, as I thought it may have been too tight and binding. When I lubed the worm and gear, I gave the whole gear a complete turn each way and there was no binding at all. This has me stumped.

Have just parked the mount and CWD is spot on, but the scope instead of pointing South is pointing East. Something is seriously amiss with the dec.
Any ideas on the one chaps, I am tearing my hair out....

[gbeal]

Not really Pete sorry, but the undulating is too regular to be much else. I can never read the PHD graphs (I use Maxim), but the feeling is some form of "periodic error".
What is "CWD"? Your second to last sentence has me stumped as well, (not the hair tearing), why is the scope pointing east instead of south?
Gary

[multiweb]

Couple of questions Pete. What's the image scale on your guider set-up. I mean what are we looking at? +/- what? Regardless DEC has to be as tight as you can get it without binding. Too much backlash in DEC is not advisable. Your graph indicates a very rapid shift in DEC with PHD bumping the mount real hard on a periodic basis.

That can be a tight spot in the worm or a balancing issue or a bad alignment causing a shift too rapid in DEC, or as simple as a greasy clutch disc, but the drift would be random and continuous.

To diagnose these things the first thing you need to do is disable the guide output in PHD, do a basic drift alignment and see what happens without guiding then take it from there. There are too many variables to try to diagnose everything at once and you need to go through a process of elimination.

Forget what you did on the night thinking I've already checked that. You probably were tired, frustrated, wanted to start imaging asap and missed a lot of things. Been there done that. :)

[Exfso]

Thanks chaps. CWD= counterweight down. I know balance is not an issue as I spent quite a while getting that correct. My guidescope is an ED80, and the guide camera is the Orion Starshoot Autoguider.
Marc, not sure as the what you mean relating to the image scale +/-??
I know the clutches are dry and clean as I did them with the service. Drift alignment should be pretty good as I have registration marks on my pier/mount, so it is just a matter of plonking the mount back on the pier and aligning the registration marks. If it is out, it would only be a poofteenth, and should definitely be able to be corrected by guiding. Also the fact that the mount does not end up in the proper parked position has me stumped as well. :screwy:

[multiweb]

Ok - I guided on an Orion ED80 with a Q-guider so you have an image scale of approx. 1.8asp. Looking at your graph then the amplitude of the jumps is not excessive.


So what happens when you graph in PHD and let the mount track with the guide output disabled?


Different issue. You might have your limits or home position set wrong. I wouldn't worry about that right now. Are you using Gemini?

[Exfso]

Yeah Marc, using Gemini. I have not changed the limits at all and up until last week it used to park home position CW down pointing at SCP.
Re disabling the guide output, I will try that tonight after I re check drift alignment.

[multiweb]

No worries. That will give you a good indication if it's mechanical or software related. Get the mount to track as good as it can first then start guiding and see what happens. Might be good to do a cold start in the CWD position and erase any model so you start afresh as well.

[Exfso]

Thanks Marc, I have been only doing cold starts since I got back from camp. I reset the home position today from the hand controller, that should fix one problem, but if you start the mount cold from the CWD position and scope pointing at SCP, it should recognise that as the parked position.

[multiweb]

Indeed it should. But don't worry about that yet. That won't effect your tracking.

[Exfso]

I got the home position all sorted. Did a check on polar alignment tonight using the drift method, no star movement in 10 mins, so I reckon I am pretty well polar aligned.
The PHD graph is still shocking. I disabled the guide output and the dec and ra graph chased themselves off the scale.
Beginning to think it is either my Gemini guider port, dodgy starshoot autoguider, or a cable issue. I have a toucam which I will connect tomorrow night via gpusb and see if that will work ok. Beginning to clutch at straws now. :shrug::shrug::mad2::mad2:

[gbeal]

Pete,
look on the bright side, if you can track for 10 minutes, then at least on good nights you can image, just need shorter subs.
OK, take it one step at a time. Try the whole new setup for guiding (ToUcam, GPUSB, another cable) then slowly mix and match the existing parts.
Does the Gemini have an "optimum" guide speed, and if so was that set. I know that with my EM200 I use the guide speed, but for quick slewing or centring I use the H/S setting. Now if I forget to return to the guide setting it goes wild.
Gary

[multiweb]

When the PHD guide output was disabled you say the dec and ra graph chased themselves off the scale. Just oscillations? No drift correct? Because if you are polar aligned well enough to have no drift in 10min then you should have a fairly straight PHD graph.

[gbeal]

That's the part I couldn't understand. Slowly and surely off the graph perhaps, but not chasing/oscillating.
Gary

[multiweb]

Well I assume that if you have no star movement in 10min after drift alignment that would show as a very minimal drift in PHD over a significant period of time.

When you disable the guide output all you're left with is the worm noise. I have had instances in bad seeing when by disabling the PHD output my RA and DEC flat lined because the mount was tracking better than chasing the seeing while guiding.

If there are still problems in DEC and RA with the guide output disabled then it is a mechanical problem. Meshing, balance. Could be anything. A G11 well polar aligned should give you a very narrow graph in PHD with a small amplitude over 1 min at least at this image scale.

[Exfso]

Marc, I tried so many things last night, you are correct, the dec line was dead flat along the centre, but the ra was still jumping about. (from memory)

[multiweb]

Ok. Now we're getting somewhere. Double check your clutch discs to make sure they're not greasy. Check your meshing in RA to make sure it's not too tight and check your balance as well until you got smooth RA. Is your RA motor hot when you touch it? Change the RA cable as well to make sure it's not the cable. (swap with the DEC cable). Then you can start guiding again and see what happens. I'm pretty sure it'll be all good.

[Octane]

Marc,

John and Doug pulled Pete's mount apart at Snake Valley. Everything was cleaned and regreased.

Pete, I still think you should remove one/all of your finderscopes and retry. Humour me. :)

H

[multiweb]

Hi H, yeah I saw that. If it tracks badly on its own in RA it can be only a number of things and they're all mostly mechanical. Unless the cable's bad ( I had that) or the motor has overheated and is misbehaving now. I haven't seen a picture of the rig so hard to tell what's on it too.

[JohnG]

I have spoken to Pete this morning and I am getting him to remove everything bar the OTA and to attach his guider to that and do another test, also as he has another guider I have asked him to put that on and do an identical test as well, pending the results of this test it should eliminate whether it is mechanical/hardware or software related.

My original thoughts were a balance problem but that was eliminated at SV with a very careful rebalance of everything.

Cheers

[gbeal]

Good move John, back to a single simple refractor and guider. Get it proven from there and the rest should be simple.
Gary

[Octane]

Yay.

Look forward to seeing the results.

H

[Exfso]

I have set up the GPusb guider for tonight with the current scope setup to see what happens. If result is same, I at least know the Starshoot is ok. If all is now ok, it is the starshoot, which incidentally is less than one month out of warranty, that would be typical. Just a matter of being patient and using the process of elimination. I know for a fact balance is fine, motors were cold last night. As John said we stripped it almost completely at SV and that is not an issue. Used another set of RA and DEC cables, that is not an issue. I have a brand new Gemini battery to put in tonight, but this is just as a precaution. Not too many things left to try. Anyone want to lend me their Gemini so I can check that out...LOL.....:sadeyes:

[gbeal]

Go for it mate. Not conversant with the Gemini stuff, but why, why, would it park differently, that has me beat?
Gary

[multiweb]

If it comes to worse I can lend you my hammer ;) Works for me. Just show it to the mount and it starts tracking.

[tlgerdes]

How is your power feed?

I had my G11 do something strange a few weeks back, Goto Star 1 OK, Goto Star 2 OK, Goto Star 3 pointed to ground. Power off Cold start, Star 1 OK, Star 2 OK, Star 3 Ground.

Pulled the power cords out, re-seated them, Star 1 OK, Star 2 OK, Star 3 OK.

Bad power, makes bad Gemini :mad2:

[Exfso]

Checked with another autoguider tonight, still the same problem. Tomorrow night will strip everything off the scope except the Tak and I will use it as a guidescope this should tell if it is a balance problem. Currently I have the side by side losmandy plate with a Tak TGM guiding mount on it is an ED80 as the guidescope. If this is the problem and I doubt it is, looks like I will be doing a piggyback setup. Have had the side by side for a couple of years with no guiding issues. Got a horrible feeling it may be the Gemini guiding port, but need to get a lend of another Gemini to confirm this. It could be the RA and DEC leads, but if they were a problem, it would not slew and do all the other stuff that it is doing correctly, like pointing etc. Certainly a strange one that is for sure.:shrug::shrug::shrug::shrug::s hrug:

[multiweb]

Could you track with PHD guide output disabled? What was your graph like?

[spearo]

Trevor could be onto something
is the mount powered at 13.8 volts?
I once had weird performance
did the "reboot thing" fine since.
frank

[Phoenix]

Hey Pete - I'm not far from you as you know. I can drop round with my Gemini to test if you like. Let me know.

Cheers, nix

[Exfso]

Steve, you are a gentleman and a scholar. This really is getting to me mate.

[Exfso]

The mount is powered by a 13.8 regulated supply. Been down that road before got caught, now it is always powered by this method.:thumbsup:

[Phoenix]

Hi Peter

I'm busy tomorrow but free Friday evening where we can try out my Gemini if needed. I can bring DEC/RA motor cables, etc as well as a brand new Orion StarShoot Autoguide - never been used. If you are busy Friday, I'm happy to make another time.

We can PM with details

Cheers

[Exfso]

Sounds great to me mate.:thumbsup:

[Exfso]

Well Steve came over last night and we swapped his gemini and all cables. Problem still exists, so it has to be either polar alignment or balance, nothing else could really be the culprit. Thanks Steve, very much appreciated.

[multiweb]

Could you track with PHD guide output disabled? Can you post your graph?

[Octane]

Did you remove your finderscopes? ; )

H

[JohnH]

Wierd G11G guiding - I have had odd behaviour on occasion if the guideport on the camera (mine is a QHY5) is not initialised before it is connected to the guideport on the mount. It seems safest to always start the Gemini with the autoguider disconnected, then start your guidecam/software and then connect the guide port. If I do not do that I have seen the guideport start up with a continuous signal which the guide software will fight to correct...you can tell if this is happening as the tracking returns to normal simply by unplugging the guide cable.

Another thing that drove me almost nuts was random autoguider error messages on the Gemini display - this I tracked down to the dew heater power cable - swapped to coax and no more issues.

Just thought I would share in case it might help, I realise you have tried an alternate camera and cables already but perhaps it is the guide port - that is on the motor contol board not the handset - or did you swap that also? You could try ASCOM guiding to eliminate the guideport from the setup...

[allan gould]

As mentioned in the post above you could try ascom guiding and plug into the RS232 port. This will eliminate the guide port. The other thing I would do is to give away PhDguiding. I used to use it then as I added programs to my laptop found its performance dropped way off. I then went over to guidemaster and it worked perfectly. Went back to PhD and no go.
Got a new laptop and can use both programs to guide with no problems - go figure.

[Hagar]

Peter, Just a thought, do you get the same graph aberations on both sides of the meridian? don't change the balance or weight positions.

It could be an endplay movement on the dec worm, Checking it on both sides of the meridian sould show up if it is an endplay problem.

[Exfso]

All discussed with Doug and John G tonight. A few more things left to try. Gemini and all cables fine. Possible that I might have the wrong guiding speed set in Gemini, but it started at default when I changed the Eprom yesterday, so that should not be an issue. Going to swap the RA and DEC worms with their wormblocks, just in case one of the worms is at fault. I checked the polar alignment and it appears to be pretty well spot on. A and E numbers are a bit of a worry though...the hair tearing continues....:screwy:

[Hagar]

May be worth working through a process of elimination. It now looks like it is a mechanical issue. Swap worms and blocks around, next step would be to check gearboxes and motors, clutch thrust races and backing/tensioning plates. Pay particular attention to the endplay and float of the worms in the worm blocks. Last thing has to be a bearing replacement all round and just check every screw on the mount for tension. You could also try measuring the output voltage from your power supply, a small change in output voltage can make a big difference, particularly if it is getting down into the 12 to 13 volt range.

Good luck matey. Keep in touch.

[cfranks]

Peter, I have only just seen this thread. I live in Plympton and if you want to bring your setup here, we can compare directly with my G11/Gemini. We can even swap out various elements to do a direct comparison. I am off work until 12/4 so, if necessary, we can test during the daylight for general setup etc. PM me if you are interested.
Charles

[Exfso]

Thanks Charles, Steve came around the other night and we eliminated the Gemini and leads as being the culprits. However, I might take you up on the offer so we can do a direct comparison.:thumbsup:

[Bassnut]

Peter, Marc has repeatedly asked you for the Guide cam image scale and what the graph looks like just tracking. These factors are critical for analysis. Without this info, its just random guessing.

[Exfso]

Fred, havent been able to do a thing for nearly a week as the weather has been crud (too windy). As far as image scale goes, not really sure what you mean? I am using just the Tak at F7.7 as the guiding scope, star shoot autoguider, and absolutely nothing else connected. I was not aware that you could get the graph to work with just tracking, so I obviously have not done this one, however, just using the bullseye when not tracking, the star virtually does not move from the centre of the target. I am really beginning to get thoroughly fed up with this, makes one feel like throwing in the towel.

[multiweb]

:lol: I rest my case. :thumbsup:

[Bassnut]

OK, well you originally said the guidescope was an ED80, and Marc then guessed you had a guide scale of 1.8 asp. If the graph is in arc/secs then you certainly dont have a problem, even DEC is only 2 arc secs P/P odd and RA is very good. If its in pixels, then DEC is 3.6 arcsecs P/P, which isnt bad either. The RMS shown Im guessing is RA at 0.21 (and looks like about 1 P/P), which is friggin awesome. I dont know what 0.48 "osc index" means.

Another guess, is the graph is the wrong way round, (RA-DEC are transposed), that would make more sense, the RA as shown is suspiciously low.

The red line looks like the axis is constantly drifting (alignment?) and being periodically corrected with minimum move set to high (not attempting a correction untill its gone too far), and then the correction is too agressive, causeing an overshoot (this could also be backlash).

The "mn mo", which I guess is min move, seems to be a low number, but then I dont know what scale its on. Does "mx dec" mean dec max move?, if so, try lowering that. I cant see a DEC agr setting. Asuming the graph axis are correct, thats a worry, you definitely should be able to set DEC agressivness (or does that come up clicking the RA/DEC button?).

The graph doesnt show what the horizontal timescale is, the oscillation on the 1st graph could even be PE .

All this is based entirely on the graph you have shown (which anyway seems to show no big problem if the scale is as Marc suggested). If you visually get a bad result, then the guide image scale is nothing like 1.8asp.

You can graph whist tracking (I think), just by starting guiding (and the graph) and then pull the guide plug out.

[Octane]

Fred,

PHD Guiding allows you to graph a tracked star. You simply tick the Disable Guide Output checkbox in the settings.

H

[Exfso]

H, when I have disabled the guide output, I assume it stops the DEC, I end up with a straight line in DEC and the RA does its dance. Will see if I can get an example if the bloody cloud will nick off.
Fred, I originally used the ED 80 as the guide scope which is the normal config, however in an attempt to get rid of any possible flexure, I removed it, the Tak guiding mount, the side by side and just left the Tak stand alone to test the guiding with.
Oh yeah, H, I did remove the finder just as a joke, it did nothing...LOL

[desler]

Although, Let me start this with my thoughts for you Pete and hope a solution is found quickly.

Now my learning. H, by graphing he star in PHD without guiding, I take it your getting shown all of the mount, polar align and balance issues and trying to get the graph as small as you can in this format, will only assist in Guiding?

And Fred, guide scale of 1.8asp?? As I'm using a ed80 guide scope and qhy5, I'd like to know a little more on how you figure out the guide scale and how you use this number to improve your system or reduce guiding errors.

I know I'm a relative newbie at all this, but having travelled an amazing learning curve in the two years since I first looked through a 8 inch Dob, it's amazing how many terms are used on this site that I have no idea what people are talking about.

I have never worked in a field or had a hobby/interest where so many people are willing to give their time and share the experience. Must be we we all get so sucked in..... Oh, and by the way, Good Luck Pete!


Darren

[Exfso]

Thanks Darren, yep it is great people are interested in helping, I really do appreciate it. Attached is a graph using Steve's Gemini and as you can see it it a real crappy graph. Balance was perfect, polar alignment was good.

[multiweb]

Darren knowing your image scale on your guider is important because it is the only thing that allows you to quantify your deviation in RA or DEC by looking at your PHD graph. The lines over and under the central lines are pixels on your guider's image. If you use an ED80 (FL 600mm) with a QHY5 (5.2um pixel size) at prime focus your image scale is: 206.265/600mm * 5.2um = 1.78763asp. Now you know what 1 pixel deviation means so you know your guiding is +/- 1.8 arcsec if you stay within the top and bottom line.

[gbeal]

Pete,
while no expert in PHD, don't have one, LOL, is that graph so bad? I mean, has it produced images that are substandard? Why I ask is that the little time I have spent with PHD (and going Mac completely means I am likely to spend a LOT more soon), most of my graphs have looked similar, perhaps not quite so wavy, but similar.
"Perfect" balance worries me too, I tend to be east heavy where possible.
Gary

[multiweb]

Is this graphed with the same guider on your Tak? What's your Tak FL?
You have a major problem in DEC regardless and that's a clutch/balance issue (side by side). Your RA's not too bad though but DEC should be much less than RA.

There is one thing that didn't make sense by reading all the post in this thread. You are describing a major drift problem during guiding but as Fred mentioned looking at the graph it doesn't show any problem. That's why you need to graph this problem by disabling the guide output in PHD. Forget Gemini or any software for now. What you need to do is get this DEC and RA as close as possible without guiding so you need to polar align very well, pick a star close to the south pole for a start, then get it right. When done pick another star up the meridian and better your balance in RA.

Then you can take it from there.

[desler]

Thanks Marc, well explained!


I happen to agree with you Gary, compared to my graph, it doesn't look to bad. Although I spent a few hours last week just refining my polar alignment and getting the balance east heavy and just right, The change in the graph was quite impressive!

At the moment I'm pretty happy getting 10 minute subs with close to round stars but in the future with a better camera, I'd like to push the times out a bit, thus the search for improvement continues!!!!!!

Darren

[Bassnut]

Although I dont know what the graph time scale is, differential flex wont be a problem at such short timescales, with the FL of your refractor, thats not the problem. Flex becomes a problem over say 1500mm at 15min or more, assuming the guide scope is well mounted and the guide cam is not waving in the breeze way out on the end of a dodgy ED80 focuser without being clamped.



Just plug the scope and cam into Ron Wodaskies CCD calculator (free) and it tells you the scale , get its very easy and fast to use.
The scale helps by knowing how just how big a problem is. A graph by itself is meaningless (to see how big the problem is anyway). If Peters graph has graduations at 1 arcsec then theres pretty much no problem, if its in pixels then you need to know the scale in arc/secs/pixel. If say the scale was 4 asp then there is a problem.

Watching how the graph proceeds is also very useful, you can tell PE, backlash, stiction, alignment, seeing, balance, and how stable guide control is (control settings). From my experience, Peters 1 st graph (and it may not be the case here) DEC curve is typical of iether DEC out of alignment with wrong correction settings (slow drift, and wrong/over correction), or a perfectly balanced DEC axis with backlash.



Perfect balance is not good generally, especially if you have backlash, both axis should be slightly out of balance so they always drive one way, this eliminates back lash.

[cfranks]

I can't see a reference in the thread but is it a completely standard G11 or has it been fitted with the McLennan gearbox(es)?
Charles

[Exfso]

I meant to say re perfect balance, that I am just slightly CW heavy and slightly focuser heavy on the scope. I realise if one is perfectly balanced you would get "slop" with the worm and gear meshing, there always has to be a slight load on the worm.

[Hagar]

What sort of statement is this?


The outcome of all this regardless of the ASP scale and all the dithering about error size is that with this amount of error Pete is ending up with significantly oval stars from a mount and guiding system which didn't suffer the same problem a few weeks ago.

By removing the electronics of the gemini and guider from the list of possibilities, it leaves either, polar alignment ormechanical problems which might well include such things as Motor/encoders, worn bearings, damaged or miss aligned worms or gears or balance.
When it comes down to the mechanical list it is usually a matter of elimination to proove a piece of equipment good or bad.

Comments like that above do nothing but frustrate Pete further than he already is.

[Exfso]

Charles, the mount is totally standard except for the latest eprom upgrade for the Gemini.
Marc, not too sure why you responded as you did, I replied to Fred in the thread just prior to yours explaining why I had not supplied the enformation. I am still trying to get my head around this problem and some of the statements being raised are somewhat foreign to me and I need time to work out what you are after. I am after all an old fart and not a guru at this particular stage of fault finding. This is a bit of a long an involved process and a lot of what is being asked has been covered whilst at the SV camp when John, Doug and myself gutted the mount. I do appreciate your input, but please hold back on the sarcasm, OK....

[danielsun]

Well Pete if it makes you feel any better I have just spent the last 5 hours trying to figure out why my mount suddenly won't guide in Dec.
All of a sudden the Dec dropped off the PHD graph so I re calibrated and got an message from PHD that dec failed and will turn off, so I re meshed the gears over and over then pulled the whole Dec axis apart, checked all, reassembled so figured it must be the PHD so went back to previous version and all still the same then the last was remeshed the steppermotor gear with worm gear incase it was too tight but the clouds rolled in.
So I was hoping that I may have a breakthrough to possibly help but at this stage I am also stumped.

[multiweb]

Take it easy Doug. No need to stir the pot when there's nothing to stir. :thumbsup:


No Sarcasm Pete. Only trying to help. I'm still here aren't I? It was so bloody obvious to me that it is a simple mechanical problem that needed to be resolved from the beginning of this thread. I just asked a simple question twice and Fred picked up on it straight away because that was the very first thing that should have been checked from the word go. Reading on about swapping geminis, cables etc... was sooo painful. All it did was just confusing you even more and probably frustrated you even more. I thought that was funny what Fred posted at the time, that's all because I nearly gave up on this thread ;). I thought at the time is he the only one actually reading all the posts because it's like I'm talking to a wall? Now I'm no guru either and I've pulled my hair over tracking problems with the G11 and gemini so I can empathise with you, believe me and I have now some experience to share so I'll state a few things, feel free to grill me.

1_ When it comes to PHD guiding I have found it extremely reliable. If you can move sucessfuly the mount via GPUSB, Serial, whatever you're using from A to B, PHD WILL guide. That's a fact.

2_ If PHD doesn't guide properly and 1_ works then you have a mechanical issue, whether it's balance (too much of it or not enough of it) or clutch slippage, or (very) poor polar alignment.

Graphing you mount behaviour in PHD will tell you straight away what's wrong. Don't look at your camera viewport and think the star is not drifting, because visually you can't tell until it has moved a couple of pixels which at your image scale would be only a couple of arc seconds.

I guarantee you that if you get the DEC and RA tighter by only tracking and graphing in PHD then guiding will only be the icing on the cake. It'll work. As Doug said, you need a process of elimination. One step at a time and good enough tracking is the first step.

So if you could please post your Guider FL, camera pixel size and PHD tracking (not guiding) graph here we can have a look and work it out. :thumbsup:

[multiweb]

PHD will disable DEC guiding if the star doesn't move enough during calibration. It is likely you need to increase the Calibration step (ms) that defaults to 500 or 750ms I believe with a new installation. This needs to be increased if you're calibrating close to the pole or modify your guiders FL.

[Exfso]

I searched around and found an image scale calculator. Here are the results for the current setup using the Orion SSAG

[Exfso]

Got a bit of a sucker hole tonight to test. My interpretation is that the guiding is +/- 1 arc sec per pixel for the Tak as the guidescope, given that the image scale as per the previous calculation is 1.07 arc secs/pixel. What happens when the guide output is disconnected, is something I cant decipher. Will leave it up to you guys.
Here are a couple of graphs:

[Bassnut]

Well, Ill stick my neck out ;-).

I assume the 1st graph is guided and the last 2 arnt and all graphs are arc/secs or pixels, which doesnt matter as your scale is 1:1.

Since there is no horizontal time scale, ill also assume the guide exposures are 1 to 3 seconds odd.

The 1st graph shows 2 arc/secs P/P 0.45 RMS. The variation you see is probably seeing. This graph my friend, is pretty much the best you will see on a well tuned G11 in average urban skies, there is absolutely nothing wrong with the guiding as shown.

If you have elongated stars with that guiding, then the guiding aint the problem. It may not always be like that though, you may have an intermittent problem that did not occur during the 1st graph.

The 2nd graph (tracking only?) is also fairly normal, with drift due to off polar alignment. I cant tell how off the alignment is, because I dont know the graph time scale. The short variations there is seeing, and is almost the same as with guiding, so the guiding is fine.

The 3rd graph (tracking only?) hints at a possible intermittent problem when the RA levels off then shoots off near the end. This could be a bunch of mechanical things Marc has mentioned. IMO the drive/tracking is fine, and its an intermittent mechanical issue that out of all your graphs, is only really hinted at in the last graph.

I think Marc had it nailed all along, its a simple mechanical problem. Binding worm?, slipping clutch?

[Octane]

Fred,

That graph is atypical of a good performing G-11.

John Glossop's is often flat and doesn't deviate to even the first line (which represents 1 pixel of movement). Mine, also, when well-balanced and well drift aligned, also shows very minimal movement.

H

[Bassnut]

H

So we are clear, are you telling me 2arc/secs P/P 0.45RMS guiding with say 2-4 arc/sec seeing is 1. Shocking atypical 2.Very bad atypical or 3.Just bad atypical ?.

Even at 3000mm FL I found that guiding to be more than acceptable image wise, and was more than happy with it on my G11.

Are you sure your not talking about a flat line in perfect still dark conditions in the field?.

I think youll find 99% of astroimagers would be extatic with 0.45 RMS error H, not sure how or why you could dissagree frankly.

[mill]

Fred even my EQ6 has a way better graph than this G11 and many people have seen my phd graph while guiding.
There is definitely something wrong.
I normally get 0.20 RMS error and at SV camp i had 0.04 RMS error.
My OSC index was mostly 0.25.
Look at post #29 http://www.iceinspace.com.au/forum/showthread.php?t=53901 (this is done from my back yard).
John's G11 is even better than my EQ6.

[Bassnut]

Well, OK, im amazed you all can get near flat lines then (less than 0.2 RMS,wow)(and we are talking arc/secs right?, not pixels) on G11s/EQ6s, was way out of my league on my G11 ;-). What is your P/P?

Are your guide exposures longer than say 3 secs then?, or youd be close to chasing seeing which itself is rarely less than 2-3 arc/secs.

[mill]

Guide exposures are normally 1 or 2 seconds. (the seeing up my way is normally pretty good :) ).
If you tweak phd for your scope good enough it will almost flat line (It will take a while to get the settings just right).

[Exfso]

Fred, I was using 2 second exposures, and each of those graphs is a couple of minutes duration.

[Paul Haese]

I am gonna stick my neck out too.

The graph you see below is that of an average graph I get. In fact I don't trust this graphing at all. What matters is the round stars. Statements saying that people get flat lines is certainly inconsistent with what I see most of the time. I own a mount that has 3" from peak to peak on PE. My polar alignment is pretty good but could be better still.

I have had flat graphing and not so flat like below and each time the the stars remain the same. Personally I think too much credit is being paid to the idea of the graph.

What are your stars showing now Pete?

[Exfso]

Paul, I didn't get a chance to do any exposures tonight as the cloud started rolling in. Just enough time to check the guiding.
Martin, if you were using the same guide cam as I am on your guidescope, which I believe is a finderscope, say 150mm FL, then your image scale from the calculator I use would be around 7.4 arc secs/pixel. I would say that you should nearly have a straight line graph because if it was peaking 1 pixel above and below that would be 15 arc secs P/P. I think I am right in my assumptions here. Those more in the know can correct me if I am wrong.
This is the link to the calculator: http://celestialwonders.com/tools/imageScaleCalc.html

[Bassnut]

Exactly right Peter, nice to see the penny has droped :D..

It suddenly dawned on me after my last post ,all you guys are just comparing raw numbers off unscaled graphs (in pixels) with no regard to image scale at all. 0.2 RMS on a EQ6 makes no sense (seeing alone with 1-2 sec exposures would make this impossible) at all untill you realise its actually 1.4 arc/secs RMS (which is very good BTW :thumbsup:)

Its a bit like comparing the top speed of 3 cars useing just the raw numbers off speedos that are calbrated in Km/hr, inches per second and leagues per fortnight :P.

I can also see now why Doug, Paul and others dont put much faith in analysing guiding PHD graphs, they pretty basic as presented, without any scaling. Maxim DL has the option of scaleing in Arc/secs, which makes a hell of a difference going by the confusion this thread has generated.

H, a DSI on an ED80 has an image scale of 3asp, so multiply the numbers you get by 3, and you Martin, as Peter says, have to multiply your readings by 7.4 ;).

Once you know the scale and read your graphs in arc/secs, analysing graphs does become very usefull, as Marc is also vainly tring to drill into you lot :lol:.

So again Peter, the 1st graph in the last set of 3 (at a 1 arc/sec scale)shows more than adequate guiding.

Pauls guiding at 3-4 pixels P/P (at at guess at 1.7 asp is some 5 arcs/secs P/P and less than 1 RMS), going by the pics he posts, is also more than fine too. In fact with a refractor, guiding at anything less than 5 arc/secs error P/P is workable IMO.

[desler]

Boy, \and I thought I know what I was looking at !!!!!!!!!


Please, Using the calculator supplied by pete, using a qhy5 and ed80, I get an image scale of 1.788 app.

So therefore my graph is multiplied by that number?

So each dotted line off the centre line equates to 1 arc second, and if I spend a fair bit of time getting my drift alignment and balance just right, ie: a little heavy E, I can keep the graph within 2 arc seconds.

I have noticed a recurring bump in Dec, but it is still within this range, So, I'm starting to think that at the present time, I don't have a lot to worry about?

I don't know about you Pete, but I've got a headache just reading this stuff? and I can still take pics at the moment. Good luck Mate!

Darren

[Bassnut]

Darren. No, each line is 1 pixel, which is mutiplied by 1.78 to give the graph scale in arc/secs, which is universal in assesing guide performance, because then "the numbers" apply to anyones set up.

2 arcsec P/P (although RMS is also important) for anything under 2m F/L imaging is fine IMO. Random bumps much higher than this are not good though, can make stars elongated, even though other imaged objects such as nebula are not affected as much.

[multiweb]

Thanks for that Peter. As discussed guiding looks very good, DEC drift looks very good, RA not so good. Could you please post a couple of 4min unguided runs (full worm cycle) so we can rule out periodic error or clutch slippage/balance in RA. Then we'll know for sure and take it from there. Don't worry about DEC.

[JohnG]

I wan't going to get involved with this discussion as I have been talking to Pete on a personal basis.

This is exactly what Pete's problem was/is, this random jump, in DEC. At SV the jump was in the order of +/- 5 pixels on a time scale of 30-40 seconds with the occassional jump going off the scale, intitial conclusion was balance and that was the case and the whole mount was carefully rebalanced but the problem persisted. Everything that has been mentioned here has been tried but this random jump still remains and this is the problem. This is what is causing the elongated stars in Pete's images.

As far as PHD is concerned, every possible setting has been tried and more, the mount will settle for a short period then start the random jumps again, it has nothing to do with the worm period or the infamous 76 error problem.

The RA graph has always been well within what I would call quite acceptable, the DEC is and always has been the problem area. I, like some others here only use the graph as a quide, so long as the stars are round is what I am interested in and in the respect, my error is usually around 0.35.

These latest guiding graphs show a huge improvement over what I saw originally and are beginning to show what a normal G-11 graph should be.

Cheers

[Exfso]

It looks as though the problem has somewhat disappeared. I did 15x7mins of M20 tonight, no darks, flats or bias and very minimal PS, it appears as though the stars are nice and round and sharp.

[Paul Haese]

Looks pretty good to me. Mind you I would like to see a larger version Pete.

[Exfso]

Yeah unfortunately I cant post a larger one here.

[wasyoungonce]

Just jumping on this thread for advice guiding advice, G11/PHD.

My G11 is really behaving & guiding nicely in RA but DEC guiding starts off with an awful error~14 to 11 arc sec's. I noticed some slight elongation in my stars and I'm attributing this to my DEC.

I noticed that the error is large at the start of guiding but smooths down quickly to acceptable level. I only wait a few seconds between PHD "starts guiding" before starting exposures...maybe 5 seconds at best. Should I wait longer? :shrug:

Anyway any ideas on cause of the DEC issue?

All graphs on 05/06 Jul and I changed from 3.0s guiding iterations to 3.5 sec's on the 06 jul. RA graphs are corrected for declination angle.

[multiweb]

I usually bump the mount to dither then give it 20s minimum to settle down. The way I look at it is what's 20s more in your imaging session when you do 10min subs or more anyway.

[wasyoungonce]

Thanks Mark...This is what I'm thinking...I'm not allowing guiding to settle before starting subs?

It appears DEC does settle by itself...just takes awhile.

I like the idea of dithering subs...on my to try list.

[multiweb]

When I first calibrate PHD and it starts guiding my DEC usually goes its merry way. I then go for a cuppa come back when the backlash is gone and the worm is loaded and guiding then I check the direction of the drift, sets the guide against it and set the max dec duration to 500ms and that's it. When Neb downloads the pic it pauses guiding so DEC will go one way or the other. When PHD's back it will pick up the DEC back then start guiding again within those 20s and I get another sub started. Works quite well. Don't loose too much sleep over DEC. :)