Qkslvr
Pooh-Bah
Reged: 06/23/06
Posts: 1050
Loc: NE Ohio, US
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Seem to keep having various guiding problems.
First my setup.
I'm imaging with a C8 OTA with a 6.3 fr, and a 40D.
My cheap guide scope has a 50mm main objective, and a 600mm fl, I have a .5 fr with a SPC900 webcam.
I can get it all working, But I get various artifacts in my subs as seen in this crop.
If I don't get the doubles, I frequently get elongated stars.
RA=~Left/Right in this image.
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Mike
N8/CG-5/40D
Coming sometime/Maybe FrankenRebel
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Qkslvr
Pooh-Bah
Reged: 06/23/06
Posts: 1050
Loc: NE Ohio, US
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What I'm looking for is; is there any combination of setting that will reduce these?
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Mike
N8/CG-5/40D
Coming sometime/Maybe FrankenRebel
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MartyT
professor emeritus
Reged: 09/28/07
Posts: 517
Loc: Kansas City
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What do you get without PHD in the mix?
Looks to me like PHD is fighting with slop in your mount - either backlash or some other kind of flexure.
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Celestron CGE / C-11 (CGE-1100)
Megrez 90 FD APO / 0.8x FR/FF III
QHY8
Modified Canon 350D (Baader UV/IR Filter)
DSI Pro (guider), SPC900NC
ETX-125AT
Meade 12" Lightbridge
Astronomical Society of Kansas City
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jgraham
Postmaster
Reged: 12/02/04
Posts: 5313
Loc: Dayton, Ohio
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It looks like you may be fighting backlash in the gears. What mount are you using?
I saw something exactly like this using my LXD75 in declination using Envisage as my guiding software. In my case the fix was to reduce the dec % (a setting that accounts for the backlash in the gears). In PHD you might be able to set it up so it cotrrects in one direction only so it doesn't oscillate back'n forth.
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-John
================================================
Homebuilt scopes from 4.25-16.5"
Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130
Orion StarBlast, BinoViewers, Coronado PST
Rebel XT/XTi, DSI Pro (I & II), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC
Tasco 60mm Refractors
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Qkslvr
Pooh-Bah
Reged: 06/23/06
Posts: 1050
Loc: NE Ohio, US
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It's a CG-5 ASGT, and that was something I was going to try and correct for tonight. I had pretty good results a week or so ago with the same stuff, except since then I mounted the guide scope on a heavy swivel camera mount about midship on the OTA's front clamp, taking weight off the back. I'm going to slide it back some in the rings. Which should stop the oscillations.
Thanks!
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Mike
N8/CG-5/40D
Coming sometime/Maybe FrankenRebel
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DaemonGPF
Pooh-Bah
Reged: 03/22/08
Posts: 1428
Loc: New Mexico
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I had the same results in mine starting out. I don't know if my causes are the same, but I'll put them out there:
The first culprit was low SNR and losing the guiding star intermittently, which I fixed with a better guidescope and increasing exposure time in PHD.
Second one was backlash. When the guider would send a correction command that required the mount to move in the opposite direction of it's original approach, the backlash would cause a jump large enough to create doubles and streaks. I turned down the antibacklash setting and the issue went away completely.
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-Josh
*Orion Starblast Imaging 150mm OTA
*Orion Starblast Imaging 114mm OTA
*Meade 50mm AR short tube OTA
*Meade DSI Pro IIc
*Orion Starshoot DSCI
*CG5 mount
http://cleardarksky.com/c/AlbuqNMkey.html
My Messier Project Gallery
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Nils_Lars
scholastic sledgehammer
Reged: 01/04/08
Posts: 903
Loc: Santa Cruz Mountains , CA
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I have had a problem with my CG-5 and balance , it is hard to get just right.
There is a way to tighten the gear mesh in the CG-5 and take out some backlash but there is also a way to adjust for backlash in the hand controler.
I would also suggest taking the reducer out of the guide scope since it makes the responce slower in the corrections.
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Erik
Orion ED 80
Orion Atlas GOTO mount
Williams Optics reducer
Various eyepieces and other gear
Baytronix 80mm guidescope
Orion Starshoot Autoguider
PHD guide
Canon 400D (unmodded)
Stilleto Focuser
Tamron 75-300mm&28-80mm lenses
NexImage webcam
http://home.comcast.net/~eriknlarsen/site/?/photos/
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DaemonGPF
Pooh-Bah
Reged: 03/22/08
Posts: 1428
Loc: New Mexico
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I also force PHD to recalibrate every session.
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-Josh
*Orion Starblast Imaging 150mm OTA
*Orion Starblast Imaging 114mm OTA
*Meade 50mm AR short tube OTA
*Meade DSI Pro IIc
*Orion Starshoot DSCI
*CG5 mount
http://cleardarksky.com/c/AlbuqNMkey.html
My Messier Project Gallery
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Buhlig
member
Reged: 12/03/07
Posts: 58
Loc: Derby, KS
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I've had EXACTLY the same effect with my CG-5 and PHD. Initially I was just stumped. But, I had an interesting experience last time out that I'll share. Had everthing setup and was snapping subs right at dark...great. First sub had the same image you show here. Hmmm, that isn't so good. So I started watching PHD very carefully. It was indeed issueing dec commands about every 2 minutes or so. When it did, you could see the guidestar drift out of the box, things got hectic, then it would eventually get the star back into the box and stabilize, but it was too late, the sub was corrupted. Frustrated, I shut of dec guiding, but that just made star trails. At first glance, this appears to be backlash, bad backlash. But, I've seen PHD work before issueing commands in all directions. Here's what I did. I shut everything down, and double checked my BALANCE. I had it ever so slightly heavy in the back of the OTA, not alot, but a little. I've found if you have it heavy on the back (pushing the objective end "UP"), PHD and CG-5 don't like each other. I moved the balance slightly objective end heavy...setup everything again, and WOW! PHD was dead on, and the images were flawless. It was still issueing dec commands, but it didn't have the erratic results like before. In all fairness, I'm running some pretty beefy equipment for a CG-5, but I think everyone will agree, the heavier you run, the more important balance is. It also may vary from mount to mount. MY mount likes objective end heavy. When I run my 80ED I don't experience any of this...get the balance close and let 'er rip. Hope this helps.
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Celestron 80mm ED Apochromatic Refractor
Orion 8" Newt
Celestron 80ST achro (guider)
PHD via handcontroller interface
CG-5 Advanced GT Mount
Canon 350D
Philips SPC900NC
http://www.flickr.com/photos/derbysluggers/sets/72157605255114566/
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Buhlig
member
Reged: 12/03/07
Posts: 58
Loc: Derby, KS
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here...this looks familiar doesn't it?
Edited by Buhlig (08/20/08 08:24 PM)
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Buhlig
member
Reged: 12/03/07
Posts: 58
Loc: Derby, KS
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now, after balancing
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Celestron 80mm ED Apochromatic Refractor
Orion 8" Newt
Celestron 80ST achro (guider)
PHD via handcontroller interface
CG-5 Advanced GT Mount
Canon 350D
Philips SPC900NC
http://www.flickr.com/photos/derbysluggers/sets/72157605255114566/
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DaemonGPF
Pooh-Bah
Reged: 03/22/08
Posts: 1428
Loc: New Mexico
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I've got a few of those laying around for the same reason. Very good point about the balance.
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-Josh
*Orion Starblast Imaging 150mm OTA
*Orion Starblast Imaging 114mm OTA
*Meade 50mm AR short tube OTA
*Meade DSI Pro IIc
*Orion Starshoot DSCI
*CG5 mount
http://cleardarksky.com/c/AlbuqNMkey.html
My Messier Project Gallery
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Qkslvr
Pooh-Bah
Reged: 06/23/06
Posts: 1050
Loc: NE Ohio, US
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Buhlig, Very interesting, as I solved the problem last night, By carefully adjusting the balance so it's heavy on the camera end (SCT). Basically making sure the gears were loaded taking up the backlash.
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Mike
N8/CG-5/40D
Coming sometime/Maybe FrankenRebel
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jgraham
Postmaster
Reged: 12/02/04
Posts: 5313
Loc: Dayton, Ohio
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For a while I added a small trim weight so I could pre-load the gears one way or another. It seemed to work really well particularly if the telescope ended up pointing in a direction where the ballance was just about to shift from one side to another and it would rock back'n forth just enough to cause problems.
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-John
================================================
Homebuilt scopes from 4.25-16.5"
Meade LXD75-N6/SN6/SC8, DSX-90, ETX-60BB, ETX-125PE, DS-2130
Orion StarBlast, BinoViewers, Coronado PST
Rebel XT/XTi, DSI Pro (I & II), DSI, LPI, Electronic Eyepiece, Phillips SPC900NC
Tasco 60mm Refractors
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