ICEINSPACE
Most Read Articles
Moon Phase
CURRENT MOON Waning Gibbous
81.6%
The Sun Now
Time Zones
Sydney*
6:50 pm
Perth
3:50 pm
Auckland*
8:50 pm
New York
2:50 am
Paris
8:50 am
GMT
7:50 am




  #1  
Old 11-02-2019, 11:48 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 875
Is this a colimation issue in my refractor?

This is a sub from my Luminance Data.

Just looking at the non-symmetrical halo around Alnitak.

Is its asymmetry caused by being positioned in the top left of the image? Or should I look to my collimation?

I did check it on the night using the tube reflections method and it seemed spot on.

Cheers

Markus
Attached Thumbnails
Click for full-size image (Lum_Horsehead_180sec_cg% _offset_50_fpos_NA_-20C_offset_50_frame2.jpg)
204.7 KB63 views
Reply With Quote
  #2  
Old 12-02-2019, 01:54 AM
Joshua Bunn's Avatar
Joshua Bunn (Joshua)
Registered User

Joshua Bunn is offline
 
Join Date: Oct 2011
Location: Albany, Western Australia
Posts: 1,063
Your stars look pretty good, I would say it's cause the star is off axis.


Josh
Reply With Quote
  #3  
Old 12-02-2019, 04:16 AM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie, NSW
Posts: 4,955
It could be caused by a slight image train weight shift, if there was any flexure in your setup. Which direction was down in your image?
Reply With Quote
  #4  
Old 12-02-2019, 06:06 AM
Atmos's Avatar
Atmos (Colin)
Ultimate Noob

Atmos is offline
 
Join Date: Aug 2011
Location: Melbourne
Posts: 5,778
It’s not unusual to see reflections off-axis to look like this. The stars across the field look good so I’d say that it’s just because it isn’t in the centre.
Reply With Quote
  #5  
Old 12-02-2019, 07:00 AM
JA
.....

JA is offline
 
Join Date: Oct 2016
Location: Melbourne, Australia
Posts: 1,247
Quote:
Originally Posted by Stonius View Post
This is a sub from my Luminance Data.

Just looking at the non-symmetrical halo around Alnitak.

Is its asymmetry caused by being positioned in the top left of the image? Or should I look to my collimation?

I did check it on the night using the tube reflections method and it seemed spot on.

Cheers

Markus
It could be lens flare/reflection caused by an off axis light source or a refection from filters or even from the sensor itself. There appear to be multiple faint haloes around the star, displaced ever so slightly along a line towards the image centre, which is typical of lens/optical system flare. When these ever so slightly displaced haloes appear on top of one another they appear as an ovalish shape as a whole and I can certainly see how they could blend together to form the IMPRESSION of a collimation issue (whilst not actually being one). See attached (exaggerated) diagram.

I recall reading of an issue with reflection artifacts with the ASI1600 caused by a lack of/type of anti-reflective coating on the sensor window. I also recall the image had faint diffraction type spikes in a 4/8 spoke pattern, which are also present and similar to those in your image, but I'm not sure. The spikes may have been caused by a diffraction/reflection from the prism of an off-axis guider. Did your image also use an OAG?

To try to verify the cause, perhaps a different type of filter could be trialled, with a different antireflective multicoating. Perhaps a photographic filter

Best
JA
Attached Thumbnails
Click for full-size image (Flare Reflection.jpg)
47.4 KB21 views

Last edited by JA; 12-02-2019 at 08:04 AM. Reason: + diagram
Reply With Quote
  #6  
Old 12-02-2019, 02:56 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 875
Quote:
Originally Posted by glend View Post
It could be caused by a slight image train weight shift, if there was any flexure in your setup. Which direction was down in your image?
That's a good point.

Down was in the direction of elongation.

It was all threaded connections though, so I'm trying to think of the flex point.

I guess I could test it by rotating the focuser 180 degrees and seeing if it happens again.

Markus
Reply With Quote
  #7  
Old 12-02-2019, 03:00 PM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 875
Quote:
Originally Posted by JA View Post
I recall reading of an issue with reflection artifacts with the ASI1600 caused by a lack of/type of anti-reflective coating on the sensor window. I also recall the image had faint diffraction type spikes in a 4/8 spoke pattern, which are also present and similar to those in your image, but I'm not sure. The spikes may have been caused by a diffraction/reflection from the prism of an off-axis guider. Did your image also use an OAG?

To try to verify the cause, perhaps a different type of filter could be trialled, with a different antireflective multicoating. Perhaps a photographic filter

Best
JA

Thanks yes, microlensing is an issue in this series too (less so on the Lum channel here, but more pronounced on others). I expected to see it on this shot, so it was not a suprise. But I wanted this composition and I'm interested to try my hand at mitigating the effects of microlensing. If it all gets too hard I can always crop in, I guess.

Best,

Markus
Reply With Quote
  #8  
Old 12-02-2019, 05:32 PM
Merlin66's Avatar
Merlin66 (Ken)
Spectroscopy Wizard

Merlin66 is offline
 
Join Date: Oct 2005
Location: St Leonards, Vic
Posts: 6,630
JA, et al,
The ASI 1600 is fitted with a BK7 AR coated window.
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 05:50 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Lunatico Astronomical
Advertisement
SkyWatcher 2018 Catalogue
Advertisement
Bintel
Advertisement
SkyWatcher WiFi Adaptor
Advertisement
NexDome Observatories
Advertisement
Interest Free Finance
Advertisement
FLI Cameras and Imaging Accessories
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement