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.
What sort of statement is this? .... Comments like that above do nothing but frustrate Pete further than he already is.
Take it easy Doug. No need to stir the pot when there's nothing to stir.
Quote:
Originally Posted by Exfso
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....
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.
Last edited by multiweb; 06-04-2010 at 07:56 AM.
Reason: spelling
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.
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.
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:
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?
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.
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.
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/s...ad.php?t=53901 (this is done from my back yard).
John's G11 is even better than my EQ6.
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.
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).
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.
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
Exactly right Peter, nice to see the penny has droped ..
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 )
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 .
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 .
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.
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. 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.
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:
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.
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.
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.
. 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. 
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