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  #81  
Old 24-04-2011, 11:56 PM
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Tandum (Robin)
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I don't think guiding has anything to do with syncing of the mount. I'm sure I can guide the tak mount without having a PC/The Sky controlling the mount. Is your sidereal rate adjustable? Is it stable? It's not flicking to solar or lunar rate is it? If the rate is too high plus movement between downloads?

And here's a late night after thought, don't you have a tv guider? That doesn't use a pc so guiding wouldn't be blocked while images are downloading. That should pull image drift during download out of the equation or inversely prove that it's drifting when guiding is paused.

If you connect maxim to your scope via the observatory window, maxim will put RA/DEC, Alt/Az, FL etc etc into the fits header, then you can then analyze/pinpoint a new or old image and sync or slew the scope to the center of the image as reported by pinpoint. You need to have the scope data entered correctly under file/settings/optics and have the GSC 1.1 (corrected) installed, for it all to work well. And your mount driver should be a hub, or you could use POTH, to connect multiple tools to the mount. You could also connect it to the lesve dome controller and run a motorised roof as a shutter

I only managed to get 4 subs through a sucker hole tonight, phd is guiding though a second PC and I see no drift, but it's only 4 x 2minute subs. I'd prefer to get 10 x 10minutes worth as a direct comparison to what I have already seen before saying it's definately usb traffic causing my drift, but it sure looks like it.
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  #82  
Old 25-04-2011, 07:06 AM
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Robin,

I don't get the usb traffic theory as I would have thought this would imply that the guiding software would have to forget the original guide star position.

If the original guide position was retained and the pc simply stopped guiding during the image download wouldn't you expect to see a large guide correction after the download was complete?

Peter
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  #83  
Old 25-04-2011, 07:20 AM
gbeal
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I agree with Peter, if the guiding stopped, and assuming Herr Ponders' drift alignment was woeful, then the star should reacquire, but with the obvious consequences, of trailing while it does the reacquisition. Hmm, maybe.
"Observatory Window" as in Maxim, like Robin said. This effectively means you can calibrate where you want, and then shift to other areas without having to recalibrate again.
Gary
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  #84  
Old 25-04-2011, 07:41 AM
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If it was trailing during re-aquisition then you wouldn't see the steady shift in image position from frame to frame - just elongated stars.

Last edited by peter_4059; 25-04-2011 at 08:15 AM.
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  #85  
Old 25-04-2011, 08:27 AM
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Paul,

I'm coming into this discussion a bit late - have been away on holidays.

Can I clarify - are you guiding with PHD or Maxim?

I would expect shift between subs when using Maxim as it suspends guiding whilst downloading from the imaging camera. Unless your polar alignment was 100.00000% and no PE, there would always be some shift between subs. I do have dithering turned on and notice some large corrections in guiding as it resumes guiding after the download. It then settles back down to normal corrections. I hope it's not correcting out the dithering, otherwise what is the point of dithering?

As far as I'm aware, there shouldn't be any issues with the AP controller firmware. They don't have any modelling, so shouldn't be trying to do anything differently in various regions across the sky.

I'm wondering if you have a problem with the mount shifting depending on where you are pointing in the sky. It's well aligned when the weight is hanging in one way, and then moves ever so slightly when the weight shifts. How have you attached the 900 to your pier?

DT
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  #86  
Old 25-04-2011, 10:04 AM
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[1ponders] (Paul)
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Thanks for all the input guys.

My connections to the scope is like this.
Laptop USB>GPUSB>AP900 guideport
Laptop USB>USB hub>SXVF-H9 (connected to SX EXview autoguider via direct serial connection), DMK21
Laptop USB> Keyspan 4 port USB - serial Hub>AP900

Image aquisition> Maxim
Guiding> Phd or Maxim (via guider relays or GPUSB for the SX autoguider, or GPUSB if using DMK via Maxim. (swapping guider relay cable and GPUSB cable over as required, checked each time))

No ascom being used.

My drift alignment is very very good. >0.3 pixel/min drift (both alt and az) using DMK & VC200L via K3CCDTools. Easily achieve 3 min unguided shots with negligible Dec drift.

Standard AP PEC is on, thought over 3 min there is noticeable PE movement. Mount will need to be retrained.

The mount is well balanced and has been checked a number of times.

For the past few weeks when I have been able to get out to image my standard startup routine is:
  1. Start Laptop
  2. Hook up USB cables
  3. turn mount on
  4. select location 1 and goto (as per manual)
  5. Resume from Park
  6. Select Object;star; usually a star to the east and south (as that is where I'm likely to be imaging)
  7. goto
  8. start Maxim and/or not phd> center star in Maxim (and phd, guiderings are good and tight and 1 sec exposures will always allow me to find a good guide star when I need one)
  9. sync on star
Now normally at this point I would goto a star near the object I want to image and refine my alignment and check focus and then goto the object I want. In recent weeks I've only been shooting stuff from the E the S SE corner and at least 45 deg in elevation, 5128, 3372, 3621 etc.
  1. Image acquisition procedure:
  2. Center object
  3. Calibrate for guiding using either Phd stand alone with DMK21, or using Maxim via GPUSB for DMK 21 or SX, or maxim via guider relays using SX. Never had a calibration fail.
  4. Set image exposure times and quantities.
  5. Start guiding, start capture

My SXVF-H9 is attached to the VC200 via 2"+ diameter threaded extensions directly to the focuser and the focuser lock bolt is tight. Up until 2 nights ago my guidescope was WO72 using either a Meade flip mirror or star diagonal on SBS mount, now I'm using 50mm Stellarvue finder in over under with Losmandy guiderings tight. All have been rock solid and I was not able to find any movement in the system even giving it a good hard wobble by holding the WO or the SV. Guide Camera mountings have been and still are good and solid. Checked and double checked and checked again.

Now the pattern of movement appears to be strongly as though the initial mount movement is in equal amount south and west showing a strong movement. As the night progresses and the mount is pointing more vertically the star movement reduces gradually until it is only moving slightly as though the mount is moving southerly, but only minimally. This is what convinced me it was flexure. Now however I am not so sure.

2 nights ago I shot 5128 for 5 min and got strong SW movement as per 'normal'. Cloud came in and i slewed across the meridian to M46 (around the same elevation). I took 2 x 5 min shots and there was no sign of any pronounced flexure. When the sky cleared I slewed back to 5128 and did another 5 min shot. No movement, yet if i had stayed there, going by previous experience, it should have continued to show flexure.

Going by this experience, last night I did my normal alignment procedure and aligned on a star to the eastish but then slewed across the meridian, re synced on Sirius and then shot M46 again. No movement. I immediately slewed back to 5128 and shot 20+ x 5 min shots with no movement (barely a pixel movement between shots in Dec south) and then 17 shots of M83 again with no movement (except pixel movement in Dec south)

So by doing a calibration run on the guiding in the west first and then coming back to the east has somehow removed (?) the problem.

Oh and btw all my guiding graphs prior to 2 nights ago have always been tight and clean whether using PHD or Maxim.

Got me
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  #87  
Old 25-04-2011, 10:57 AM
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Bassnut (Fred)
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OK, just a few things in case. You must have the reverse guiding direction on flip checked or the guideing would not work on flip. Yes DL pauses guideing on image download, but you can pause imaging to allow guiding to settle after download before imaging recommences. If you dont have this delay set, stars can look not round due to the 1st few seconds of erratic guide settling of an otherwise good guide graph.

Are you useing auto darks on the guide cam?. If not, and the guide cam image is noisy, even though you slew back to a previously well guided object, it may now lock onto a hot pixel or a different dimmer guide star. Is the reslew coming back to the same guide star?.

If guiding is correct in every way and in every case, then think about this. The guide cam is the only thing the mount/DL guiding knows about, the OTA is outside the control loop altogether, its just extra weight on the mount. Any image defect in the OTA image (assuming good, no problem guiding) can only be a mechanical problem, nothing to do with the mount or DL at all.

So your left with mechanical flex/movement in scope mounting, focusers, draw tubes, mirrors, cameras (all either with the guide or OTA).

Is the guide cam solid on the back of the guide tube?. Movement of the guide cam on its scope/draw tube/focuser alone can cause OTA image problems. Remember ONLY the guide cam itself is in the guiding control loop.

Im banging on about the guide setup particularly, because I spent a long time sorting drift which ended up me bolting the guidecam to the mounting rail, that made the biggest improvement (at long FLs.) Even though your images are OK most of the time, and the inconsistancy is puzzling, there should not be the slightest dought about the whole guide set up stiffness.

Last edited by Bassnut; 25-04-2011 at 11:20 AM.
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  #88  
Old 25-04-2011, 11:08 AM
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Tandum (Robin)
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Guys, as Fred and the maxim guiding help says, guiding is paused and the guide star reaquired after download. Same for phd, the imaging camera driver will block usb so no commands are sent out. How it reaquires is the question, we all see some drift and no big corrections in PHD. Beside, if you don't know what the problem is, you find out what it isn't.

Paul, if you used the mounts ascom driver you could remove the gpusb etc and use pulse guiding for all cameras. Also I've read that button 8 on the handset adjusts tracking rate, make sure it's not sticky like Rick's handset.
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  #89  
Old 25-04-2011, 11:35 AM
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peter_4059 (Peter)
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Quote:
Originally Posted by Tandum View Post
Same for phd, the imaging camera driver will block usb so no commands are sent out. How it reaquires is the question, we all see some drift and no big corrections in PHD.
Robin,

I'm struggling to see this pause in guiding with PHD. On my mount PHD appears to carry on with 1 sec guide exposures and corrections while the QHY8 downloads (usually takes 5-10 seconds to download an image).

How can you tell that the imaging camera driver is blocking USB coms for the guiding?

If this is what is happening it is strange that the drift continues in a line - ie if the drift is caused by the guider picking up some random hot pixel or another star when it re-aquires wouldn't you expect the drift to be more random?

Peter
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  #90  
Old 25-04-2011, 01:50 PM
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[1ponders] (Paul)
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Fred, I recalibrate the autoguider each time I move to a different area and autoguider settle is on. Yes i'm using autodarks. I do hear what you're saying Fred and I'm really listening hard, true. I'm just having a hard time working out why on one night I can get 35 clean shots in one area (eg ngc3621), come back the next night to an area just south of that (NGC5128) and get 35 useless shot. Add to that if I flip the meridian, calibrate and guide over there for a few minutes, flip back to the original side I can guide all night without a problem. However I am taking your advice and looking at how i can fix the guidescope hard to the imaging OTA and looking very closely at how I can make sure the guide camera is a immobile as I can make it.

Robin I have very very little misalignment and running a 5 min unguided shot shows only a few pixels drift in dec and only PE in RA, I don't think it is likely that the problem is in reacquiring the star as in that short a period it won't have moved. Of that I am confident. I have taken the GPUSB out of the equation a couple of times by guiding directly from the guider relays straight to the mount. It didn't make a great deal off difference so in that respect I'm confident of using the gpusb. I have also used it via Maxim and Phd, and while phd still has a few question marks hanging over it I'm fairly happy with the GPUSB. I could try ASCOM but I've not used it before in any significant way and I'd rather not try to lean something new while I'm sorting this out. Maybe one day.

I've also checked the guide rate and it is set to 1x sid. Once I've finished processing them I'll upload some shots from over the past couple of weeks with their details on equipment/hardware/software combos. I must say that I was very happy with last nights efforts after the initial swap from one side to the other.
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  #91  
Old 25-04-2011, 02:02 PM
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Is the 1x sidereal what you would use? I use something like .5x.
Gary
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  #92  
Old 25-04-2011, 02:54 PM
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Seems to work fine everywhere else Gary. I'd normally use 0.5 with the G11
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  #93  
Old 25-04-2011, 03:23 PM
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Well, suppose if it works....... Just seemed high that was all, and given a to and fro motion, high isn't really what we are after.
Good luck.
Gary
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  #94  
Old 25-04-2011, 03:39 PM
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0.5 is a default standard. 1.0 can be a bit aggresive and harder to tune with long FLs. Once you pick a value stick with it, because PEC must be done with the same value. If you change it, you have to redo PEC.
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  #95  
Old 25-04-2011, 11:33 PM
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I got 15 x 10minute subs tonight with phd on a second PC and I still see drift here, so my usb blocking concept is shot down in flames. In almost 2.5 hours it has moved 23 pixels right and 51 pixels up at 1623mm FL, yet the phd log says the guide star hasn't moved at all. It's guiding at around 350mm. It not a problem but I'd like to know why it is so?
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  #96  
Old 25-04-2011, 11:37 PM
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Yep its a real head scratcher Robin. At least your getting round stars.
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  #97  
Old 25-04-2011, 11:55 PM
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Quote:
Originally Posted by Tandum View Post
I got 15 x 10minute subs tonight with phd on a second PC and I still see drift here, so my usb blocking concept is shot down in flames. In almost 2.5 hours it has moved 23 pixels right and 51 pixels up at 1623mm FL, yet the phd log says the guide star hasn't moved at all. It's guiding at around 350mm. It not a problem but I'd like to know why it is so?
Differential flexure
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  #98  
Old 26-04-2011, 12:01 AM
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Quote:
Originally Posted by [1ponders] View Post
Yep its a real head scratcher Robin. At least your getting round stars.
Not all the time Paul, check this one out I've pretty well sorted this eq6 as a travel mount, the tak will go back in next week.

Quote:
Originally Posted by Bassnut View Post
Differential flexure
So if I track it down to the west the movement should be in the opposite direction? Won't happen tonight, it's overcast now and has already rained straight into the dome while I wasn't looking
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  #99  
Old 26-04-2011, 12:14 AM
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Gee that looks familiar
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  #100  
Old 26-04-2011, 03:47 AM
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Fred was right. The clouds cleared and I tracked it west and it drifts the other way. So it's flex. You can see in that last animation, as the scope approaches zenith (I think it went from 40 to 80 degrees before it clouded over and rained ) the drift changes from left/right to straight up. This animation runs from about 50 down to 20 degrees West so the vertical movement is missing, and a few may be out of sequence but still ..... Very Interesting ....

And if this is flex then it must be happening all the time and it must be making the stars bigger than they should be. Hmmmm.
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Last edited by Tandum; 26-04-2011 at 03:58 AM.
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