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  #61  
Old 23-04-2011, 11:37 AM
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Visionoz (Bill)
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Hi Paul

Still got hair left?
Sorry to hear that it's still a problem - well I don't envy you at all as I know how that's sooooooooooo frustrating!! Mine was easier to resolve!

I'll be keen to know what ails it though!! Never too much to learn new things

Well good luck with the hunt, hope you resolve it soon!

Cheers
Bill
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  #62  
Old 23-04-2011, 12:04 PM
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Bassnut (Fred)
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Paul

That video looks like flexure. Ive just noticed your useing SBS guide scope and OTA at 1800mm. I tried SBS at that FL, the flex was shocking, similar to yours, unfixable. I ditched it and mounted the guide scope on the OTA, much better.
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  #63  
Old 23-04-2011, 12:09 PM
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[1ponders] (Paul)
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I'm seriously thinking of going that way next Fred, but how do we explain the shifting focus. Loose mirror clip?
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  #64  
Old 23-04-2011, 12:51 PM
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Paul,

I feel your pain - I've gone through a similar process over the past couple of years trying to eliminate this type of movement between subs. My last mod was to replace the main ota rings with some beefy ones from Parallax. I've reduced the flexure a lot since I started (now about 1 pixel per 10 minutes) but have added a lot of weight to the mount components in doing so.

One thing you might like to try is Deep Sky Stacker live - it calculates the drift from one sub to the next as you aquire the images and presents the RA and DEC drift on a chart. The chart shows pixels of drift and you can watch this as the scope tracks the object to see whether it is getting better or worse. I found the drift was worse as I moved away from the meridian.

Good luck!

Pete
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  #65  
Old 23-04-2011, 01:11 PM
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[1ponders] (Paul)
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Thanks Pete. I might give that a go if changing the setup doesn't fix it. The thing that gets me is that it seems to be only in one part of the sky, the interesting part atm
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  #66  
Old 23-04-2011, 04:37 PM
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Hi Paul,

If your autoguiding and its drifting then you must have flexure somewhere. There must be something you overlooked ?

Terry
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  #67  
Old 23-04-2011, 06:03 PM
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How about trying a different scope, any scope, just a different one. Does the issue only become evident at the 1800mm or so focal length. Burgle a long newt, try that, or even a refractor and a short barlow?
Take the mirror flop issue out of the trial, just to see if it is possibly that.
Gary
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  #68  
Old 23-04-2011, 06:29 PM
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Quote:
Originally Posted by [1ponders] View Post
I'm seriously thinking of going that way next Fred, but how do we explain the shifting focus. Loose mirror clip?
SBS guiding is no good at 1800mm FL, whether you do it now or later makes no diff, youll have to in the end anyway (or OAG). A (guide) refractor is heavy at the front and the RC heavy at the back, different flexure=extra grief.

When (not if) you mount the guide scope on the OTA, bolt everything down hard (incl guide cam). No rings, clamps. If the guide cam is waving in the breeze miles from the scope with a wobbly focuser/draw tube, then bolt the Guide cam to the guide scope mount rail too, Guide focus is not critical, doesnt need adjustment after initial focus, just bolt it down after focus, reduce drift.

Focus is a different grief, worry about that after you ditch the SBS.(BTW the weight saving ditching the Losmandy SBS gear will help no end).

At 1800mm FL solid is everything.

Last edited by Bassnut; 23-04-2011 at 06:47 PM.
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  #69  
Old 23-04-2011, 06:49 PM
Hagar (Doug)
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Paul, I am unsure what cameras etc you are using for capture and guiding etc but could it be that during download your camera driver doesn't allow any other USB while reading/downloading. Your guiding then may well restart a few pixels off the original guide position.

Not sure how these things work but just a thought.
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  #70  
Old 23-04-2011, 07:39 PM
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The drift/movement is too much for that Doug, though I have though about that. I'm using either DMK21 and GPUSB, or SX EXview guider through the SXVF-H9 relays and have also tried it with GPUSB. Doesn't seem to make any difference.
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  #71  
Old 23-04-2011, 08:06 PM
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Paul
I had exactly your problem with my 72mm WO guidescope as I had almost perfectly round stars but gradual drift between exposures. Droves me nuts and so I went to an OAG and was able to do 20-30 min subs. Anyway I still liked using the WO scope and it's handy if I want to do a wide field shot so I looked carefully at the system that I was using.
Believe it or not it was a 2c fix.
Underneath my connection between the WO scope - extention tubes and DSI camera, I figured that this is where I was getting a small amount of flexture.
So to stop this I placed a small bolt underneath the DSI which screwed into the mounting plate on my 10" scope. I then screwed the bolt up so that it contacted the DSI and put a little pressure on it so that it would negate any sag in the system.
Fixed and I can now do 20 min subs at 2500 mm using the WO guidescope. So what I'm
suggesting is to firmly anchor the camera end of your guidescope setup - like JohnG did
to minimize the amount of flex in the system.
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  #72  
Old 23-04-2011, 08:48 PM
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Ok, modification for tonight.

Removed the WO and the SBS plate. To reduce weight even further I used a Stellarvue 50mm finder for a guidescope and the SX ExVeiw as the guider. I mount the SX with Losmandy guiderings on top of the VC.

First show was 5 min Centaurus A. No change, still drifting in the same direction and the same amount as previous. Cloud then came in so I swung over to M46 (similar alt to Cent A) and took 2 x 5 min shots. Hardly a pixel movement between the two shots. I then swung back to Cent A and managed 1 x 5min shot before the cloud came in. Perfectly round stars.


??????? Its got me stumped.
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  #73  
Old 23-04-2011, 10:26 PM
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Quote:
Originally Posted by [1ponders] View Post
Ok, modification for tonight.

Removed the WO and the SBS plate. To reduce weight even further I used a Stellarvue 50mm finder for a guidescope and the SX ExVeiw as the guider. I mount the SX with Losmandy guiderings on top of the VC.

First show was 5 min Centaurus A. No change, still drifting in the same direction and the same amount as previous. Cloud then came in so I swung over to M46 (similar alt to Cent A) and took 2 x 5 min shots. Hardly a pixel movement between the two shots. I then swung back to Cent A and managed 1 x 5min shot before the cloud came in. Perfectly round stars.


??????? Its got me stumped.
Now your not making sense. Hard bolt everything (incld guide cam), wiggle everything (anything remotely loose?, at ALL). If not, kill yourself. I suspect yr cheating, How can one thing be within 1 pixel and another not?. Assuming your looking at the guide graph ALL THE TIME and its not going nuts.

Your not trying hard enough.............Or your mirror is flopping around, unlikely
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  #74  
Old 24-04-2011, 06:35 AM
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What I was saying Fred was that after the change over of guidescopes and mounting I shot 5 min of Cent A. The result was that I had the same amount and direction of movement as previous. Then due to cloud I swung over to M46 to see if I had the same problem on the opposite side of the meridian at around a similar altitude. I took 2 x 5 min shots. Both shots had perfectly round stars and the mount didn't move between the shots (ie hardly a pixel movement between shots). I then slewed back to Cent A and managed 1 x 5 min shot before the clouds moved in. The stars showed as round, no movement between the shots.
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  #75  
Old 24-04-2011, 12:10 PM
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Got me stumped too. Try another scope, to reduce/eliminate flop. How long can you image without guiding, can you go 5 mins? If so, try that, taking the guiding out of the equation.
Could be that cheap mount of course, perhaps go back to the G11, LOL.
Hate to say it, but I can see an OAG beckoning. I am even thinking to try one myself, as I am getting similar but not as bad as yours (cheaper mount helps here I figure).
Keep trying though, and listen to your Uncle Fred and Gary.
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  #76  
Old 24-04-2011, 01:33 PM
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Paul, I get movement between subs and always thought it was due to usb traffic stopping while images where downloading. I made an animated gif of 10 x 10minutes subs from last week. If it's clear tonight I'll guide with another pc to prove my usb theory. However you seem to have a lot more movement than me and I'm using the eq6 at the moment.

[edit]
Doesn't look good for tonight. Looks a lot like rain clouds out there
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Last edited by Tandum; 24-04-2011 at 04:58 PM.
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  #77  
Old 24-04-2011, 03:24 PM
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Paul,

Here are a few screen shots from Deep Sky Stacker Live showing the drift from frame to frame - most of what I'm getting is in RA - 18.5 pixels in one hour. The third image shows how much of the image has been imapcted by the drift - the light blue line shows the difference between the start and end position.

Pete
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  #78  
Old 24-04-2011, 07:34 PM
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I noticed something last night and thought I might try an experiment tonight. Last night I was getting plenty of drift going straight from startup to alignment to imagine in the problematic SE corner. Then I slewed to the other side of the Meridian and did a couple of 5 min shots there. No problems there. Slewed back to the SE and managed 1 5 min shot with no drift.

Tonight after doing my alignment I went straigth to M46 and did two completely clean 5 min shots, no drift. Slewed back to NGC5128 and have completed, so far, 17 x 5min shots with no large S and W drift as before. There is a very slight movement (couple of pixels if that) southward but that is it. Its almost like I'm using a different mount.

Could this be a mount firmware issue rather than flexure? Could it be that for some reason it doesn't like to guide in that area first up and going somewhere else "clears" (cant think of a more appropriate term) some conflict somewhere??? Not knowing anything about how this stuff is written or acted on I'm only guessing. But it seems a bit strange that it guides pretty well perfectly, in a spot that I've always had problems with, after initiating guiding elsewhere first????? Does that make any sense?
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  #79  
Old 24-04-2011, 08:12 PM
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Well if nothing else at least you a work around.
Do you have to do an alignment at the start anyway? What I mean is, can you just turn the mount on, and push it to 5128 instead, find it with the finder and go from there. This eliminates the alignment phase, something else to consider.
As well, you talk about guiding in two different areas, do you calibrate the guider each time, or do you rely on the brain within Maxim to do this? If so, do you have the Observatory window connected? Or am I barking up the wrong tree here?
Gary.
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  #80  
Old 24-04-2011, 08:45 PM
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[1ponders] (Paul)
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The alignment phase is simply a sync so the mount knows where it it. Start up, select location, resume from park, goto star and sync. Done.

Yep always recalibrate when changing areas. Observatory window? Roll off roof.
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