#1  
Old 25-04-2013, 02:48 PM
White Rabbit's Avatar
White Rabbit
Space Cadet

White Rabbit is offline
 
Join Date: Feb 2007
Location: Sydney
Posts: 1,411
What is causing my stars to look like this?

Hi guys.

After upgrading my focuser to a Moonlight Focuser my stars are coming out rather strangle. I also upgraded my camera at the same time so it could be the camera. I suspect it to be reflections in the draw tube but thats pure speculation, could it be pinched optics somewhere. My image train is as follows.
STF 3800m/WO Flattner reducer .86/Astonomik 2" CLS filter/ orion premium refractor 102 714mm F7.
I never had this issue when imaging with my 5D MKII and GSO focuser so it has to be the focuser or the camera.

Here is in image crop so you can see the star close up.

Thanks
Attached Thumbnails
Click for full-size image (Possible focuser reflections.jpg)
47.7 KB237 views
Reply With Quote
  #2  
Old 25-04-2013, 02:54 PM
DavidU's Avatar
DavidU (Dave)
Like to learn

DavidU is offline
 
Join Date: Jul 2007
Location: melbourne
Posts: 4,835
Did you collimate the scope after the focuser upgrade?
Reply With Quote
  #3  
Old 25-04-2013, 03:25 PM
White Rabbit's Avatar
White Rabbit
Space Cadet

White Rabbit is offline
 
Join Date: Feb 2007
Location: Sydney
Posts: 1,411
No, it's a refractor, i wouldn't be game enough to try.

Thanks
Reply With Quote
  #4  
Old 25-04-2013, 03:42 PM
DavidU's Avatar
DavidU (Dave)
Like to learn

DavidU is offline
 
Join Date: Jul 2007
Location: melbourne
Posts: 4,835
You need to collimate the new focuser.
I put my laser into the focuser tube and made a white paper circle the same diameter as the dew shield. The paper circle would have a pin hole dead center if you use a compass. Most good focusers have collimation adjustments. Just adjust it so the laser red dot is dead center of the paper circle and your good to go.
I suspect your lens is in collimation but the new focuser is not.
cheers

Quote:
Originally Posted by White Rabbit View Post
No, it's a refractor, i wouldn't be game enough to try.

Thanks
Reply With Quote
  #5  
Old 25-04-2013, 03:50 PM
White Rabbit's Avatar
White Rabbit
Space Cadet

White Rabbit is offline
 
Join Date: Feb 2007
Location: Sydney
Posts: 1,411
Ah, thanks. I'll give that a go.

I have a laser collimator for my Newts I suppose I could use that one, correct?

Thanks again.
Reply With Quote
  #6  
Old 25-04-2013, 03:53 PM
DavidU's Avatar
DavidU (Dave)
Like to learn

DavidU is offline
 
Join Date: Jul 2007
Location: melbourne
Posts: 4,835
Yep.
http://www.cloudynights.com/ubbarchi...6/Main/1083000

Quote:
Originally Posted by White Rabbit View Post
Ah, thanks. I'll give that a go.

I have a laser collimator for my Newts I suppose I could use that one, correct?

Thanks again.
Reply With Quote
  #7  
Old 25-04-2013, 03:57 PM
pmrid's Avatar
pmrid (Peter)
Ageing badly.

pmrid is offline
 
Join Date: May 2008
Location: Cloudy, light-polluted Bribie Is.
Posts: 3,665
While you're at it, it would be worth double-checking that you have your distance between the reducer and sensor correct. Not sure what the distance is for the WO .86 but I'm sure you can get it from their website or similar.

Having done that, have a look at how you achieve focus. Do you use a Bahtinov or the FWHM or HFD numbers in Maxim? Make sure you have achieved the best focus you can and have another look. I know these sound basic things and I'm probably teaching granny to suck eggs.

Peter
Reply With Quote
  #8  
Old 25-04-2013, 04:25 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Peter is onto it. But I am also thinking, could this perhaps be well-bloating in the camera too?

My focusing is purely by hand, using FHWM method in Maxim or APT. I will generally take about 30 minutes to focus, as I allow each minimum value position to settle for 5 minutes to see if it changes much, and remember that when I lock off focus, that it MAY change (since the screw applies pressure and will shift the drawtube fractionally in or out)

It does look like a slight focus issue, (perhaps focuser as mentioned, hence why I RARELY will change to an aftermarket focuser), but perhaps a bloat in the camera???
Reply With Quote
  #9  
Old 25-04-2013, 05:20 PM
White Rabbit's Avatar
White Rabbit
Space Cadet

White Rabbit is offline
 
Join Date: Feb 2007
Location: Sydney
Posts: 1,411
I'll need to do a bit more research on the subject but from inserting my 2" laser colimator that I use to climate my newts, the laser appears pretty much dead centre. I'll need to measure it properly (as much as you can with a ruler ) but it looks pretty good to me.

The image was pretty well focused with a mask, I would imagine that an out of focus image would mute the effects of poor colimation.

Also I'm pretty sure I have the distance between the camera chip and the flatter correct as the images have a pretty flat field.

I'll post some results tonight from ccd inspector. I just purchased it last week and haven't delved into it to deeply as it looks like a steep learning curve.


Thanks guys.
Reply With Quote
  #10  
Old 25-04-2013, 06:35 PM
Terry B's Avatar
Terry B
Country living & viewing

Terry B is offline
 
Join Date: Mar 2006
Location: Armidale
Posts: 2,789
I'm not sure what the problem is. The image is of a saturated image of a bright star that is slightly octagonal. It seems to have even diffraction rings all around it. If it was a collimation problem then the image would not be even.
It is a refractor so no diffraction spikes should be present.
Are there any non circular baffles in the scope or focuser?
This is a similar effect to what the aperture ring makes with a camera lens.
The only other think I can think of is that the light from the saturated star is bleeding along the lines of pixels in the camera. I don't know what camera you used but does it have microlenses on the CCD?
It may be an effect from the antiblooming in the camera.
Reply With Quote
  #11  
Old 26-04-2013, 10:50 AM
jjjnettie's Avatar
jjjnettie (Jeanette)
Registered User

jjjnettie is offline
 
Join Date: Feb 2005
Location: Monto
Posts: 16,738
Clutching at straws here, but have you checked for spider webs inside your focuser?
Reply With Quote
  #12  
Old 26-04-2013, 12:03 PM
Shiraz's Avatar
Shiraz (Ray)
Registered User

Shiraz is offline
 
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,918
it's probably diffraction from the microlenses on the KAF8300 CCD. http://www.cloudynights.com/ubbthrea...5/Main/5391241

Seems to be a minor effect on the brightest stars and FWIW I think it looks quite attractive.

Last edited by Shiraz; 27-04-2013 at 01:52 AM.
Reply With Quote
  #13  
Old 27-04-2013, 09:08 PM
White Rabbit's Avatar
White Rabbit
Space Cadet

White Rabbit is offline
 
Join Date: Feb 2007
Location: Sydney
Posts: 1,411
Thanks for all the replies. Having done a bit of reading on it I think Shiraz is correct about the micro lense on the ccd.
A bit disapointing as there doesn't seem to be a work around.

Thanks all.

Sandy
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 06:05 AM.

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