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  #41  
Old 02-03-2011, 07:08 PM
gbeal
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Aw, heck Ken, keep it simple for the old fella.
Gary
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  #42  
Old 02-03-2011, 07:42 PM
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[1ponders] (Paul)
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I intend to do a sweep of the whole sky Ken from about 15 deg up all the way to zenith north to south in about roughly 20deg increments . I can get the rough azimuth readings from the Dec readings in the fits header.
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  #43  
Old 20-04-2011, 09:49 PM
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Update:

Not so slowly pulling my hair out here.

I've attached a number of images over a few different nights. I've been attempting to get some imaging done since I first described this problem.

I've been through and removed anything I think can be causing flexure. I've tried to guide with phd and with maxim DL 5 using DMK21 and GPUSB

The first image is a single 5 min image of M83 (you all know where it is in the sky atm in the evening) taken on the 13th of April. Then next is a straight addition of the following 4 images.

The next 8 images were taken on the 15th of and shooting all over the sky. All are 3 min images and the only one that shows any sort of trailing is Omega Cent

(cont)
Attached Thumbnails
Click for full-size image (M83_001.jpg)
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Click for full-size image (M83_003.jpg)
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Click for full-size image (IC539 (Medium).jpg)
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Click for full-size image (M4 (Medium).jpg)
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Click for full-size image (M5 (Medium).jpg)
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Click for full-size image (NGC2658 (Medium).jpg)
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Click for full-size image (NGC3372 (Medium).jpg)
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Click for full-size image (NGC5139 (Medium).jpg)
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  #44  
Old 20-04-2011, 09:54 PM
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[1ponders] (Paul)
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(last 2 images incl here)

The last three images were taken tonight. Each is a stack of 3 min subs except for M46 which is 5 min subs. NGC3621 was high almost due east and M46 is 45 deg ish almost due west.

First NGC3621 was guided using PHD and the second using Maxim as was M46.

M 46 did not move a pixel. All stacking done in PS to add them directly.

I'm really totally lost as to what can be going on here
Attached Thumbnails
Click for full-size image (NGC6067 (Medium).jpg)
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Click for full-size image (NGC6584 (Medium).jpg)
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Click for full-size image (NGC3621_PhD_guided (Medium).jpg)
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Click for full-size image (NGC3621_Maxim_Guided (Medium).jpg)
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Click for full-size image (M46_Maxim_Guided (Medium).jpg)
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  #45  
Old 20-04-2011, 10:20 PM
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h0ughy (David)
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to me it looks like it is binding on an axis then releasing, or its pushing too much in one way like the calibration is out. move your cables away from electrical interference or sit in the lotus position and meditate on the fact that you are not the only one. it occasionally does it with me - and some times it just has a massive leap like the tectonic plates releasing a heap of energy.
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  #46  
Old 20-04-2011, 10:32 PM
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Merlin66 (Ken)
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Paul,
can you check for me...
If I use CdC to monitor the direction of movement it seems to be in elevation?
(Would need more precise time etc)
If this is the case then it could infer than gravity plays a part - something sagging?
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  #47  
Old 20-04-2011, 10:42 PM
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mithrandir (Andrew)
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Paul,

H0ughy's cable theory is good.

Is there any correlation between the declination and tracking error? The closer to the pole, the worse the tracking?

With that theory, NGC3372 should be worst and the Messiers best. The RA balance or a cable pulling tight might be part of it which could mean if NGC5139 is bad, anything else being shot at a similar alt/az should be too.

On another couple of groups, the discussion seems to agree that as long as your polar align is good (not necessarily perfect), for high dec targets you can guide on just about any part of the sky within about 30 deg of there. With more available pixel movement the guider can be more stable.

Andrew
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  #48  
Old 20-04-2011, 10:57 PM
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Moon (James)
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Paul
I hope you fix this soon.
Can you remind me what scope this is?
James
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  #49  
Old 21-04-2011, 09:01 AM
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[1ponders] (Paul)
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Quote:
Originally Posted by Moon View Post
Paul
I hope you fix this soon.
Can you remind me what scope this is?
James
The whole setup is VC200L with SXVF-H9 on Losmandy SBS with WO72 FD and DMK21 for guidescope. The DMK is held by a star diagonal (used to be meade 1.25" flip mirror. swapping it out to the star diagonal didn't make any difference). All sitting on the AP900. I swapped guide rings the other day. Rebalanced and checked all connections. Everything is snug with no snagging or slop that i can detect.

Quote:
Originally Posted by mithrandir View Post
Paul,

H0ughy's cable theory is good.

Is there any correlation between the declination and tracking error? The closer to the pole, the worse the tracking?

With that theory, NGC3372 should be worst and the Messiers best. The RA balance or a cable pulling tight might be part of it which could mean if NGC5139 is bad, anything else being shot at a similar alt/az should be too.

On another couple of groups, the discussion seems to agree that as long as your polar align is good (not necessarily perfect), for high dec targets you can guide on just about any part of the sky within about 30 deg of there. With more available pixel movement the guider can be more stable.

Andrew
It does seem to be worse the closer I get to the pole but not always. Generally though its when pointing east to south. Yet if you look at M4 its spot on and even omega doesn't look too bad. But NGC3621 (spiral from last night) is not that far away. Polar alignment is excellent with 2-3 min unguided through the VC.

Quote:
Originally Posted by Merlin66 View Post
Paul,
can you check for me...
If I use CdC to monitor the direction of movement it seems to be in elevation?
(Would need more precise time etc)
If this is the case then it could infer than gravity plays a part - something sagging?
No nothing snagging in the cables at all. I've checked and triple checked that.

I can shoot almost anywhere in the sky and it seems to work fine, with the exception of E to S. The direction of the drift always seems to be down and left which corresponds to moving the mount W and S (well they are the buttons I push to get same movement). And there doesn't seem to be much variation in direction or slope of drift.

Quote:
Originally Posted by h0ughy
to me it looks like it is binding on an axis then releasing, or its pushing too much in one way like the calibration is out. move your cables away from electrical interference or sit in the lotus position and meditate on the fact that you are not the only one. it occasionally does it with me - and some times it just has a massive leap like the tectonic plates releasing a heap of energy.
I'm really sure its not cables Dave, and I'm confident in the balance. But for you I'll check them again

Initially I started using phd last night and then swapped over to Maxim. The initial movement was huge in the subs and then seemed to settle down. I guess its time to start changing stuff around. Put just the VC on with a self guide SBIG. If that works try over and under with the WO and DMK. I can hear Gary screaming in the background OAG, OAG, ....but I don't have one atm so I'll just have to use what I have.
Thanks for the help guys. Fingers crossed for a clear night so I can keep on trying
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  #50  
Old 21-04-2011, 10:28 AM
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Moon (James)
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Did you keep the Maxim DL guide log file? I think it's called track.log.
It would be interesting to see it.
James
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  #51  
Old 21-04-2011, 12:35 PM
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Yep I've included a screen shot of phd as well from early in the night. I thought I did one of the graph for maxim but it doesn't look like it
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Click for full-size image (phd Graph.JPG)
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File Type: txt Guide Log_Maxim2.txt (42.4 KB, 7 views)
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  #52  
Old 22-04-2011, 03:42 AM
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Visionoz (Bill)
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Paul

If you are using the VC200L perhaps you should look carefully at the drawtube end where you insert the 2" nosepiece which has the 60mm-to-50.8mm diameter black ring with the 2 thumb screws - This I think is the weakest part of the Vixen focuser and is very dickey!!

When I first got started into imaging I was frustrated over the many failures with my many attempts which was caused by movement in the manner you described - even after checking for flexure and everything else including changing the mount which didn't solve my issue.

I had by chance handled the 5D one night whilst it was already set up and it wiggled slightly; mind you ever so slightly and I thought that it might be worth looking into because no matter how tight the 2 screws were the camera still wiggled slightly - had machined out a replacement ring out of brass with a tapered wall surface and a mating split ring that slipped over in the middle and was locked into position by a threaded cap-like cover ring which when tightened applied pressure onto the split-ring which closed tighter and tighter around the nosepiece because of the tapered surfaces (sort of like an olive locking principle used in plumbing joints) - and my troubles disappeared - I'll have to look for the pixs to give you an idea of what I'm talking about if you think that this might be the likely cause, can't remember where I saved them but I can take new pixs, np!

The flip-mirror 2" nosepiece with the very slight "safety" undercut is not very stable either when locked on that black ring and you can imagine that as the scope pans the sky over the period of imaging the transitional changes with the weight hanging off the end will shift along and it would definitely result in issues

I don't have the wiggling issue when using the focal reducer because I use the original Vixen Canon Wide Adapter and as you know that black ring is taken off because the focal reducer is screwed in its place instead and then the CWA which has 3 thumb screws and very solidly holds the camera - don't know whether when using CCD (as I haven't yet used one on the VC200L) is different experience or all the preceding I've posted is OT (and I do apologise if it is)

HTH
Cheers
Bill
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  #53  
Old 22-04-2011, 08:35 AM
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[1ponders] (Paul)
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Thanks for your information Bill, and its definitely not OT as I will be using a modded 20D at times.

I have had my suspicions that the focuser draw tube may well be a part of it. Initially I had the SX attached similarly to how you describe, but have now attached it by threaded extenders directly to the drawtube (without any noticeable improvement) . One of the issues I have with this scope is that after focusing and I lock down the drawtube the image moves and goes out of focus. Consequently I have to have the tensioning knob set quite firmly when focusing (using motor focuser)

This is a second/third hand scope and when I bought it (sight unseen) it was not in good condition. I had to send it back to Japan to get the mirror reground as well as recoated. While it was there they informed me that there was a non-standard fine focuser knob attached and that the focuser shaft was bent, as was the rack. If the dollar gets to 1.10 I'll likely put in an order for a FT focuser. Or should I wait until it hits 1.25

Last night after refocusing (not just a touch up of the previous focus but racked it out and back in again) and paying attention to the amount of pressure being exerted by the screw, I took 150 min of NGC3621 with hardly more than a couple of dozen pixels movement in declination. A vast improvement on previous nights efforts!
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  #54  
Old 22-04-2011, 11:28 AM
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I used to get sudden tiny 'jumps' between exposures. It was the shutter momentum shifting the camera by a few micron due to non absolutely rigid mounting between camera and optic. That is a tiny movement in the bayonet coupling of the camera!

As long as it does not occur during exposures it does not matter.

Bert
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  #55  
Old 22-04-2011, 01:37 PM
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[1ponders] (Paul)
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Unfortunately Bert I don't have a shutter on this camera. I don't mind the small movements sideways or even random ones (auto-dithering ) but its when it happens during shots or moves a substantial distance so that the object being imaged moves away from the center of the frame. On some nights I've had the object move 1/4-1/3 the distance from the center along a SW corner diagonal. Last night though it hardly moved at all, a couple of dozen pixels to the south in Dec. With luck it will be clear again tonight and I can check the focuser theory a bit more
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  #56  
Old 22-04-2011, 02:22 PM
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richardo (Rich)
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Hi Paul, just to jump in here,
if you're getting 2-3min unguided, and wow, through the F9 VC200L 1800FL, and you've checked all your flexure issues (like chasing the white rabbit), it still could be the VC's tube flexing??.. slight mirror movement.. fine line to over tightening those mirror clips and not having them tight enough..I know this scope.. and these were issues I found.

If not, perhaps you must be over correcting on your guiding. If using 1 sec exposures for guiding, this would be too much intervention by the guider if your unguided is this good. Too much correction will tend to be chasing the seeing, and or the small amount of movement in the setup.
Rule of thumb I've found, use 10%(or there about) of what you can do unguided. Try 3- 6 sec guider exposures.... see how this goes.. try reducing the aggressiveness of the corrections... watch the error graph in Maxim.. it will tell you if your over correcting, just mess with aggressiveness setting and watch the graph when you try different settings.. reset your peak values and see if things get better.
Maxim works very well for guiding and you have options to refine.

I think you'll find things will be better with longer guider exposures this way the mount will be doing the work and the guider will intervene periodically.

It's all experimental stuff with guiding and chasing down flexure.. there are fixes for the VC200L and it's mirror movement (ok for back in the days of just visual observing)... removing the top 'L' of the clips and just use silicone to hold the mirror in by the sides (or even a mirror sling). Also using good quality rings to hold the tube to the mount rather than the poxy attachment plate on its bottom.

Anyway, hope some of this may help.

Cheers
Rich
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  #57  
Old 22-04-2011, 08:26 PM
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[1ponders] (Paul)
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thanks for the info Rich, yeah I'm pretty good on my drift alignment . I'm not sure if I mentioned that I've got a FR in train of the WO/dmk so I'm guiding at around 300mm. The VC itself has a losmandy D plate top and bottom to help with rigidity of the tube and mounting. The whole scope has just come back from Japan for a complete reworking of the mirror so I would hope the clips have been tensioned correctly.

I think I might just have nailed it tonight though (I really hope so). I did a focus with the button just snug, and was getting the usual diagonal trailing, though to a much lesser degree than normal. I tightened the button up (stuff the focus) and everything is looking pretty good. Its strange though that this problem is only occuring in one part of the sky.
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  #58  
Old 23-04-2011, 12:55 AM
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Quote:
Originally Posted by [1ponders] View Post
I think I might just have nailed it tonight though (I really hope so). ....and everything is looking pretty good. Its strange though that this problem is only occuring in one part of the sky.
Quote:
Originally Posted by Visionoz View Post
... and you can imagine that as the scope pans the sky over the period of imaging the transitional changes with the weight hanging off the end will shift along and it would definitely result in issues ...
Paul, like I said that might bear some truth in it

Like yourself I also now use a motor-focuser, Losmandy saddle-plates, Peter Tan's custom rings and also tighten the tension down "tight-enough" and no more problems so far

My 2cents worth

Cheers
Bill
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  #59  
Old 23-04-2011, 11:02 AM
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[1ponders] (Paul)
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Well there's one theory out the window. I'll post an animation later but I took 38 x 5 min shots last night and every one of them except for possible the last half a dozen are useless. I'm starting to think that the mirror is moving. I couldn't get a decent focus at the start of the night, but I got it as close as I could, tightened the focuser as carefully as I could without shifting focus and let it run.

The stars were blobs and moving diagonally, during the night the drift got less, the stars got tighter until at the end with the scope pointing nearly vertical the stars were tight and the drift almost negligible but sideways in dec direction.

Will post animation later. Bit a processing to do to get it ready
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  #60  
Old 23-04-2011, 12:07 PM
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I repositioned the scope a couple of times during the night but apart from that I didn't adjust anything. You can clearly see in the animation the change of direction of the movement and the shift in focus that I hadn't noticed before. I've added a comparison of a crop of 4 shots. The first two on the right are of early in the run, the 3 is halfway through and the last is the final shot. There is a noticeable difference in the focus. which i don't think has to do with seeing.

BTW this is Cent A from 19:30 to 22:00 (Alt 42 deg - 70 deg approx)
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