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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 574
Loc: Austin, TX
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Last night I threw out half my subs that looked like this example. Does it look like tracking error and if so, would autoguiding help?
In the other subs I have nice perfectly round stars for 90 seconds of exposure.
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Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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nofxrx
Pooh-Bah
Reged: 07/12/05
Posts: 1409
Loc: palm bay,florida
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I take it this was with your ASGT/C8?
Cant tell too much from the image size...
But it looks to me to be drift,did you do a good drift alignment?
Usually tracking/PE errors look ridgid.
These stars look to drift in a straight line towards the bottom of the frame with no spikes to the left or right which WOULD indicate PE...
even a very good alignment will show some drift over time at that F/L...or wind,balance etc.
I think A/G is the perfect solution for you,along with good drift alignments.it will NOT correct balance issues or improper polar alignment or wind etc. but it will with work give you at least(hopefully)95% rate of acceptable tracking.
Since I started A/G'ing with any scope I have only thrown out focus/framing images,and MAYBE 1 out of 10 from possible wind/balancing issues.
I am no expert on imaging but I hope some of this helps...
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Brent Oliver
3 Wonderful dogs: Sadie, Kara and Ozzie
Celestron C10-N///C9.25///Orion 80ED///WO ZS66SD White
Celestron CI-700 & ASGT Eq. Mounts
Nikon D40Xa///SBIG ST-402ME/Class 1/CFW///DSI-PRO...
My Gallery
Ohh yeah,and a VERY undersanding wife!! 
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s58y
Post Laureate
Reged: 12/12/04
Posts: 4832
Loc: Eastern NY
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I'm assuming this was unguided? If so, polar misalignmwent shouldn't affect some subs and not others (unless they were separated by at least a few hours).
I suppose it could be PE in the mount at certain worm positions but not others, loose mirror, loose camera mount, wind, walking near the scope, earth tremors, cat rubbing on the tripod, etc. -- anything that affects some subs but not others.
Autoguiding is certainly worth a try. I don't recall the last time I had to throw out an autoguided sub for tracking problems. Before I started autoguiding, I had to throw out a lot (but I was using a barndoor tracker back then  )
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Hutech 30D, SBIG ST-402 autoguider
SV80S, SV66 guidescope
AP900, G-11, Barndoor tracker
http://www.pbase.com/s58y
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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 574
Loc: Austin, TX
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Instead of drift alignment I used the Polar Align function from the hand controller. I usually can go 150 seconds without problem, as I am limited by light pollution. But lately it seems like my mount is giving me fits. Maybe it's time to tear it down and tighten everythinig up. I do detect some slop in both axes that wasn't there a few months back.
But I think autoguiding is in my future for imaging at a dark site or during a new moon.
Thanks for the advice, guys!
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Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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nofxrx
Pooh-Bah
Reged: 07/12/05
Posts: 1409
Loc: palm bay,florida
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Have you tried looking at all the images in sequence to see if they drift to one side of the frame? I guess I mean is there a pattern to the bad frames or are they all over the place...
s58y is right about it not being drift,it does look more like subs of mine that I have tossed out from bumping the scope(even the shutter slap at your F/L)or even walking next to it,or a light gust of wind...unless you have a Paramount in an OBS with a concrete pier you will evetually learn "the walk" as I call it,carefully positioning yourself so that you cause as little earth movement as possible when starting/stopping an exp. or checking A/G etc...
I hope,for your sake, it is not a serious problem with your mount.Maybe just needs to be taken apart,tightened up and regreased...
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Brent Oliver
3 Wonderful dogs: Sadie, Kara and Ozzie
Celestron C10-N///C9.25///Orion 80ED///WO ZS66SD White
Celestron CI-700 & ASGT Eq. Mounts
Nikon D40Xa///SBIG ST-402ME/Class 1/CFW///DSI-PRO...
My Gallery
Ohh yeah,and a VERY undersanding wife!!
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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 574
Loc: Austin, TX
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It's an interesting question about the image drift. I spent maybe 15 minutes trying to get the globular in the center of the view. It's usually not that hard but it was just about at zenith, I even checked to see what time it passed the meridian. Talk about a sore neck!
Anyway, while slewing toward the target, it looked like the camera was about to hit a tripod leg, and sure enough....Ding! It loosened the T ring adapter but it didn't seem like anything else whas damaged.
Long story short, the image was centered nicely when I began, but after 2 or 3 subs it shifted to one side and stayed there the rest of the night. It suggests to me something is loose.
Last time I took off the drive covers I saw how the motor gear had some wobble so I tightened everything up and that took out all the slop. I also noticed the screws had no lock washers or locking inserts. This time I'll get some loctite.
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Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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Patrick
Postmaster
Reged: 05/16/03
Posts: 6776
Loc: Franklin, Ohio
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Jeff,
We need some more information. What telescope were you using...what focal length? I would guess that yes, autoguiding will help, but it depends on what focal length you're shooting. With a very long focal length on the CG5-GT even guiding may not tame the PE.
Patrick
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Discovery 10" f/6 Split Tube Dob
Celestron C6 SCT
Denk Binoviewers
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Oberwerk 9x60 Binocular
Celestron Regal 8x42 Binocular
Canon 30D DSLR
Mini EQ1
My Astronomy Pages
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Jerry3672
Vendor - Quantum Astronomy Products
Reged: 01/20/08
Posts: 279
Loc: Lexington NC
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Jeff- My first guess is balance. if you were near Z and crossed the balance point of you scope, then the backlash in the gears went from climbing to falling in direction. This would explain why your image stayed once it had shifted.
Crossing the meridian is tricky. Autoguiding will bring the image back to the center, but you may still have a few frames that jump around due to backlash.
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Meade LXD75-SN-8
DSI Pro
Sony H7
Canon XSi 450D unmod
www.spike-a.com
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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 574
Loc: Austin, TX
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Hi Patrick,
This sub was taken with the SV102ED at 710mm focal length. I would guide with the AT66ED.
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Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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Charles
Post Laureate
Reged: 06/12/03
Posts: 4111
Loc: Enterprise, AL
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I agree that it looks more like a shift than a drift because you definitely seem to have a definite start of the image where the star made an image and then a stopping of the shift where the star made another image with a streak connecting them. Usually when I had a drift the light looked constant across the drift. Yours looks more like a shift. Been there got that t-shirt and it sure makes for a frustrating night, but hopefully you will learn from it. Imaging for me was filled with many a frustrating night, but I always (in most cases) learned something new.
Good Luck.
Charlie
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Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 1850
Loc: Piedmont, California, U.S.
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When I see subexposures like yours--where it almost looks like you have a misaligned "double exposure"--I don't think of drift issues or even periodic error. Also, if this were a problem with your alignment you would have seen it in all of your subs not just half of them.
Somehow you have gotten a sudden shift in the image. This could be due to a balance issue, or due to wind, or due to binding in the worm wheel and worm. I'd recommend you check the balance first. A lot of mounts require that the balance be set very carefully, and some mounts benefit from a slightly "east heavy" balance. I can't speak to your mount in particular since I have no experience with it. If that doesn't resolve the issue, make sure all the gears are meshing smoothly with a minimum of backlash but (most importantly--much more important than minimizing backlash) no binding. Even slight binding will cause the drive to "jerk" slightly as it tracks. It won't be enough to be perceived visually, and probably won't be enough to make the motors stall, but it can easily throw off the occasional subexposure.
Best of luck solving the problem!
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- Jared Willson
- Fluorostar FLT-110 w/ TEC optics
- Vixen VC200L
- Astro-Physics Mach1 GTO
- Stellarvue SV80S
- Takahashi Teegul SP Mount
- STL-11000
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Patrick
Postmaster
Reged: 05/16/03
Posts: 6776
Loc: Franklin, Ohio
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Quote:
This sub was taken with the SV102ED at 710mm focal length.
What else did you have on the mount? Or just the 102ED?
Patrick
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Discovery 10" f/6 Split Tube Dob
Celestron C6 SCT
Denk Binoviewers
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Oberwerk 9x60 Binocular
Celestron Regal 8x42 Binocular
Canon 30D DSLR
Mini EQ1
My Astronomy Pages
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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 574
Loc: Austin, TX
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Patrick, I only had the single scope on the mount.
--------------------
Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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Jeff in Austin
professor emeritus
Reged: 02/26/07
Posts: 574
Loc: Austin, TX
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Thanks for all the suggestions! I'm betting it's either balance or something fixable with a bit of tinkering.
--------------------
Stellarvue SV102ED
Celestron C8-SGT XLT GoTo
Astro-Tech AT66ED
Canon 50D unmodded, TC80N3 timer, Stiletto Focuser.
DMK21AU04.AS
Coronado PST (Lunt LS60THa on order)
Supportive family, including First Grader w/ scope, curious toddler, and lovely wife.
Sponsor of Austin CSC, Austin CalSky.
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