#1  
Old 04-12-2009, 02:32 PM
leinad's Avatar
leinad (Dan)
Registered User

leinad is offline
 
Join Date: Feb 2008
Location: Perth, WA
Posts: 1,307
Star Elongation begone!

Well not quite..

There are stars elongated from top-right to bottom-left corners appearing and I'm not sure why. the main stars look round; but fainter stars are elongated right through the image but only from one corner to its opposite crnr.

I've seen this both with and without the focal reducer.
I've checked weight, balance, changed PHD settings.

I'm thinking maybe this is focuser tilt? But how could this be?

I turned tracking and sidereal off and took a 2min exposure to see if it was drift, but the stars drifted from bottom-right to top-left; the opposite of the direction of these elongated stars.

I'm running VC200L; ST80 piggybacked(DSI Pro guided).

When I slewed the controller in DEC and RA; the stars on the screen would move parallel NSEW, so the camera is straight.

Has anyone come across this before ?

http://i611.photobucket.com/albums/t...s/ngc-2516.jpg

Reply With Quote
  #2  
Old 04-12-2009, 02:52 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
That's weird indeed. You can eliminate a few things though. It's not your guiding and your camera/focuser is square. What's left is the optics. It doesn't look like it's coma. I've never see coma only on opposite corners and not the others. I have no idea what it could be. Astigmatism maybe? But then again it should show in other parts of the picture and pretty much all your stars are in focus. Something's not straight somewhere but hard to tell. Slight mirror misalignment maybe? (as in optical axis not matching)
Reply With Quote
  #3  
Old 04-12-2009, 02:54 PM
DavidU's Avatar
DavidU (Dave)
Like to learn

DavidU is offline
 
Join Date: Jul 2007
Location: melbourne
Posts: 4,835
Read this post.
http://www.iceinspace.com.au/forum/s...ad.php?t=53356
Reply With Quote
  #4  
Old 04-12-2009, 03:07 PM
leinad's Avatar
leinad (Dan)
Registered User

leinad is offline
 
Join Date: Feb 2008
Location: Perth, WA
Posts: 1,307
Hmm read the other post.

But if it is focuser tilt, I'm baffled why it causes this affect from one corner to the other; opposite the motion of star drift.

P.S I guess one option is to play around with the focuser tilt screws, and see what changes occur.
Reply With Quote
  #5  
Old 04-12-2009, 04:03 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by leinad View Post
Hmm read the other post.

But if it is focuser tilt, I'm baffled why it causes this affect from one corner to the other; opposite the motion of star drift.

P.S I guess one option is to play around with the focuser tilt screws, and see what changes occur.
The other post was a problem I got by taking the camera off the focuser and putting it back. Something was not square. In your case I don't think it's a tilt because usually you get the whole side of the field good and the opposite elongated. In your case it's like one diagonal is ok the other elongated.
Reply With Quote
  #6  
Old 04-12-2009, 04:21 PM
Garyh's Avatar
Garyh
Amongst the stars

Garyh is offline
 
Join Date: Jun 2006
Location: Glen Innes, N.S.W.
Posts: 2,867
Maybe the scope needs collimation,
Looks like coma showing?
Reply With Quote
  #7  
Old 04-12-2009, 05:25 PM
bojan's Avatar
bojan
amateur

bojan is offline
 
Join Date: Jul 2006
Location: Mt Waverley, VIC
Posts: 6,932
This looks like out of focus combined with astigmatism to me (pinched optics?). Could be collimation as well, but not likely, as the effect goes diagonally all the way through the image.
I had this problem with cheaper lenses..
Also with my MTO1100-A, before mirror relaxing exercise.

I do not think this is guiding.. guiding was OK. If it was, you would have the problem everywhere on the frame. This is a problem with optics.
Reply With Quote
  #8  
Old 04-12-2009, 07:22 PM
leinad's Avatar
leinad (Dan)
Registered User

leinad is offline
 
Join Date: Feb 2008
Location: Perth, WA
Posts: 1,307
In this image from the same night, it can be seen throughout the image.
http://s611.photobucket.com/albums/t...nt=canopus.jpg

Ok it probably isn't focuser tilt. I checked my old photos and it's still there; this leads me to believe the mirror may actually be pinched too tight; either by the mirror clips; or by the collimation push/pull screws.

I guess I could start by adjusting the push/pull screws.. loosening them up and imaging at same time to see what affect it has.

Then if nothing changes; pull the mirror out, and loosen the mirror clips. Guess I should give the mirror a quick bath at the same time.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 10:43 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Advertisement
Testar
Advertisement
Bintel
Advertisement