#1  
Old 07-12-2018, 04:00 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
Orion Nebula Defect

Hi, I've recently "Completed" my astrophotography setup, finally getting a guide-scope and whatnot. Any way, I figured I'd start on something easy and interesting and try get some good capture time of the Orion Nebula.

Anyway, I've come to find that the star Hatysa located within the boundaries of the nebulousness is causing a lopsided Halo defect that I'm not sure how to handle.

Pointing closer to Hatysa causes the halo to shrink but causes the nebula to be framed less than ideally, where nebulousness is now also being effected by vignetting.

Here is a single example of 40 or so stacked 3min subs, darks + flats. I cropped a lot of my vignetting but haven't done any editing.

Click image for larger version

Name:	005edit - wbset2.jpg
Views:	112
Size:	92.9 KB
ID:	237391


Im using a Celestron 8se OTA, 0.63x focal reducer, Astronomik CLS CCD filter followed by the celestron CRing thingo to mount my DSLR.
Im thinking maybe the Light pollution filter is bouncing light back to my focal reducer but that's a stab in the dark (get it hahaha).

Happy for any input and critique. Hoping to collect some more data tonight to add to this, perhaps more 3 min exposures at ISO 1600 (same as this) to get more subs and later on ill take some with lower ISOs to better show detail in the centre and then have a crack at aligning it with photoslop

Cheers!

EDIT: Cant get the image to display for some reason. Always have this problem...
EDIT2: Got it

Last edited by assbutt94; 07-12-2018 at 04:57 PM.
Reply With Quote
  #2  
Old 07-12-2018, 04:35 PM
Gavin1234
Registered User

Gavin1234 is offline
 
Join Date: Mar 2018
Location: Sydney
Posts: 204
So it appears on the same star, even when it’s framed differently I.e. it’s not moisture on part of your imaging train?

To attach an image to these posts they have to be under 500mb
Reply With Quote
  #3  
Old 07-12-2018, 04:54 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
Quote:
Originally Posted by Gavin1234 View Post
So it appears on the same star, even when it’s framed differently I.e. it’s not moisture on part of your imaging train?

To attach an image to these posts they have to be under 500mb
Yes, I've had it happen to other stars before, Even when I wasn't using a focal reducer and they would be out of frame, the halo would encroach in. I dont think it's moisture as I dont think it's getting cold enough for any to form and I havent seen any evidence of moisture drying on glass.
I no longer suspect it's light bouncing forward from my LPF as thinking back, it's happened without the FR.

Also worked out adding photos
Click image for larger version

Name:	005edit - wbset2.jpg
Views:	38
Size:	92.9 KB
ID:	237390
Reply With Quote
  #4  
Old 07-12-2018, 04:59 PM
Paulyman (Paul)
Registered User

Paulyman is offline
 
Join Date: Nov 2017
Location: Unanderra
Posts: 42
That’s a reflection of the star, I get exactly that shaped reflection on my Evolution 6 when close to a bright star such as Alnitak. Can’t help with how to deal with it in processing unfortunately as I’m still starting out on that as well. But I’m sure someone will be along to help with that. Good luck, image looks good despite the reflection.
Reply With Quote
  #5  
Old 07-12-2018, 05:08 PM
Startrek (Martin)
Registered User

Startrek is offline
 
Join Date: Dec 2017
Location: Sydney
Posts: 679
If your in suburban Sydney ( bortle 7 to 8 sky ) and using a DSLR ( which I do Canon 600D) I find capturing lots of short exposures without the filter gives you a better outcome when stacking and post processing
Try 40 to 60 subs @ 25 to 40 sec with ISO 800, you still capture enough data
Iíve tried 5 minute, 3 minute , 2 minute and 1 minute subs at ISO 400 / 800 and the end result is to much noise and a massive blown out core which you canít clean up
Your DSLR sensor temperature with long subs is probably around 39 to 45 degrees but at short subs with pause and delay it should be sitting around 32 to 35 degrees, this does help
With shorter subs you can try layering in your post processing as well ( Iím still learning this feature )
Hopefully tonight Iím going for 60 x 30 sec subs and 15 darks at ISO800
Good luck !
Reply With Quote
  #6  
Old 07-12-2018, 05:43 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
Quote:
Originally Posted by Startrek View Post
If your in suburban Sydney ( bortle 7 to 8 sky ) and using a DSLR ( which I do Canon 600D) I find capturing lots of short exposures without the filter gives you a better outcome when stacking and post processing
Try 40 to 60 subs @ 25 to 40 sec with ISO 800, you still capture enough data
I’ve tried 5 minute, 3 minute , 2 minute and 1 minute subs at ISO 400 / 800 and the end result is to much noise and a massive blown out core which you can’t clean up
Your DSLR sensor temperature with long subs is probably around 39 to 45 degrees but at short subs with pause and delay it should be sitting around 32 to 35 degrees, this does help
With shorter subs you can try layering in your post processing as well ( I’m still learning this feature )
Hopefully tonight I’m going for 60 x 30 sec subs and 15 darks at ISO800
Good luck !
I used to take subs in the exposure lengths you've suggested as i bought the equipment i needed slowly and was unguided for a long time. My camera's ISO provides a similar SNR as a 600D at ISO800 (going by DXOmark anyway).
I haven't edited a 3min exposure yet, but just opening the stack in photoshop seems like it will need less editing to have more detail than any of my short exposure stacks. Granted my first attempt at editing was those short exposures of Orion, so maybe I could do that data a bit more justice.
Hopefully I may even be able to use them to layer onto the longer subs like you've suggested.

I thought that the heat would be the same at the end of varying length exposures, as the camera uses the exact same method to count and process the information the sensor collects.
I'll slap a temperature probe from a cheap set of multi-meters on the camera tonight because now I'm curious and I need help not falling asleep.
I have a 25s pause between exposures, and I keep the screen off so that is doesn't generate heat.

Im also in Sydney, the sky's look good tonight, Good luck!

Quote:
Originally Posted by Paulyman View Post
That’s a reflection of the star, I get exactly that shaped reflection on my Evolution 6 when close to a bright star such as Alnitak. Can’t help with how to deal with it in processing unfortunately as I’m still starting out on that as well. But I’m sure someone will be along to help with that. Good luck, image looks good despite the reflection.
Thanks!
Reply With Quote
  #7  
Old 17-12-2018, 06:31 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
I still had the issue the other night however I was able to minimize the extent of the halo by aiming closer to the bright star.

I took a couple exposures at 800 iso, I'll take some more in the future at lower exposures to gain more detail around the core and to bring out the trapezium.

I took some test shots of NGC 253 the other week with the same optical train without issue but there were no stars as bright as the ones in frame for M42.

Could my sensor being well past the correct backfocus distance be my issue?
Reply With Quote
  #8  
Old 17-12-2018, 10:21 PM
xelasnave's Avatar
xelasnave
Gravity does not Suck

xelasnave is offline
 
Join Date: Mar 2005
Location: Tabulam
Posts: 11,351
It looks groovy..a solar flare☺
Learn to doctor these things with photo shop...I have turned yhe bad shots around making them a challenge to save.
It is a great image.
Hope you sort the problem.
Alex
Reply With Quote
  #9  
Old 08-01-2019, 12:10 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
Just an update
I have tried to edit two different exposure stacks together.
Also had a crack at removing some of that halo in photoshop.

It definitely could be better, I'll have to keep playing with the data whenever I want something to do.

Exposing Dust
43x181s ISO 1600 Field Flattener - 3/12/18
26x181s ISO 1600 Field Flattener - 7/12/18
Darks + Flats +Bias used
Total Integration at this exposure 3h 16m 5s

Exposing for core detail
204x9s ISO 400 Field Flattener - 28/12/18
Darks Flats and Bias used
Total Integration at this exposure 30m 36s
Attached Thumbnails
Click for full-size image (3+7-12-18 001 1600iso 2.jpg)
124.9 KB34 views

Last edited by assbutt94; 08-01-2019 at 12:28 PM.
Reply With Quote
  #10  
Old 08-01-2019, 10:42 PM
Mickoid (Michael)
Registered User

Mickoid is offline
 
Join Date: Feb 2016
Location: Melbourne, Australia
Posts: 547
I got a similar effect on this one using a Tamron f 8 mirror lens the other night. Don't know what causes it, maybe focus?
Attached Thumbnails
Click for full-size image (OrionsSword.jpg)
175.1 KB37 views
Reply With Quote
  #11  
Old 10-01-2019, 06:59 PM
RyanJones
Registered User

RyanJones is offline
 
Join Date: Jun 2018
Location: Melbourne,Australia
Posts: 515
Different star, same halo .....

I just thought I just had bad subs but mine is identical to yours.

odd....
Attached Thumbnails
Click for full-size image (orion defect.jpg)
44.4 KB23 views
Reply With Quote
  #12  
Old 10-01-2019, 08:43 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
Quote:
Originally Posted by Mickoid View Post
I got a similar effect on this one using a Tamron f 8 mirror lens the other night. Don't know what causes it, maybe focus?
Mickoid, you seem to have halos on some other stars too (although smaller and fainter).
I actually googled Tamron f8 mirror lens because I had no idea what that is. I've never seen anything like it! That's a cool bit of kit!
I did a bit of reading about it and saw this review.
Interestingly reading that review, they mention funny looking Bokeh, and when I saw their image it looks very much like your Halo.
Perhaps your focus wasn't close enough?

Just for reference I used a Bahtinov mask and my rings persisted over multiple nights, each night had a few focus check every hour or so.


Quote:
Originally Posted by RyanJones View Post
Different star, same halo .....

I just thought I just had bad subs but mine is identical to yours.

odd....
Just curious RyanJones what telescope and camera did you use to capture your images? It seems your Halo is eccentric like mine too.
I also had halos coming for the star yours is, it just was further away from the nebula then the star causing most of my problems and not as bright so it wasn't my main concern.

So far the list of things I think it could be causing or contributing (for me anyway) is:
  1. Incorrect back-focus causing field to not be flat, making the star bloat weird - The fact moving the star closer to center reduces the halo makes this my best guess as the field is flatter towards the middle. The less flat the field the worse it gets?
  2. Collimation not good enough?
  3. Internal reflections (very doubtful)
  4. It's just really damn bright and the 8SE maybe doesn't have mirror coatings that can handle it well???
Reply With Quote
  #13  
Old 10-01-2019, 09:33 PM
RyanJones
Registered User

RyanJones is offline
 
Join Date: Jun 2018
Location: Melbourne,Australia
Posts: 515
I was using my C5 and Canon 5d. So both using SCTs. I've used the OTA since without changing or cleaning anything ( because I didn't see anything that needed it ) and it hasn't reappeared.
Reply With Quote
  #14  
Old 14-02-2019, 08:22 PM
assbutt94
Registered User

assbutt94 is offline
 
Join Date: May 2018
Location: Sydney
Posts: 36
I checked my 8se's collimation a couple weeks ago and it was out by a little bit.
This is likely a contributing cause.
I haven't tested with my camera to confirm due to having acquired an 8" EdgeHD.

This was also out of collimation and I also got the halos on a test image. Correcting the collimation seemingly made it far less noticeable (I haven't stacked, edited and stretched the test exposures).

I used this guide to collimate

Here is the last edit resized and cropped down a bit. I haven't removed the rings well enough but I'm happy with the result regardless. I'll improve on it next year.

Thanks for everyone's input, clear skies!
Attached Thumbnails
Click for full-size image (3+7-12-18 001 1600iso 3min edit - bkg wb - strtch - stacking22-Recovered4 - selective stretching.jpg)
129.3 KB17 views

Last edited by assbutt94; 17-02-2019 at 08:00 AM.
Reply With Quote
  #15  
Old 16-02-2019, 11:38 AM
gb44 (Glenn)
Registered User

gb44 is offline
 
Join Date: Jul 2012
Location: Gold Coast
Posts: 85
IMHO thats an artifact originating from the imaging train and its internal reflections.

It would be processed out with dithering at capture and sigma median combine for stacking in post-processing. Ryan's vignetting would disappear with flats likewise... the marvels of calibration.

Cheers
GlennB
Reply With Quote
  #16  
Old 16-02-2019, 12:10 PM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 1,659
Going back to the start of this thread. I have EXACTLY the same problem, the only thing our setups have in common is the 0.63 reducer. The loop that Alnitak produces on a long exposure is spectacular. I had it with the old 350D I used to use and still have it with the ASI294.


I am hoping to do some testing tonight if the sky allows, I might do a with/without reducer test on a bright star just at the edge of the frame.
Reply With Quote
  #17  
Old 16-02-2019, 12:20 PM
rcheshire's Avatar
rcheshire (Rowland)
Registered User

rcheshire is offline
 
Join Date: Apr 2010
Location: Geelong
Posts: 2,579
That's a nice image
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 01:55 AM.

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