#1  
Old 26-09-2020, 10:41 AM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
Example of 1600mm microlensing

Thought I might post this for people deciding between a 1600mm and 294mm so they could see how microlensing issue resent in the 1600mm affects a final lrgb image. I haven't really noticed it in narrowband however. This is from an Esprit 100 F5.5 refractor so there should be no diffraction spikes but the bright stars to the lower right are showing diffraction effects.
Attached Thumbnails
Click for full-size image (PSX_20200926_093308.jpg)
196.9 KB168 views
Reply With Quote
  #2  
Old 26-09-2020, 02:23 PM
glend (Glen)
Registered User

glend is offline
 
Join Date: Jun 2013
Location: Lake Macquarie
Posts: 7,033
David, of course Orion (M42) is notoriously difficult to process correctly, easily fixed in Photoshop using a layer mask. I believe the 294 has significantly more issues than the 1600, such as the AMP glow and poor sensor cooling scene as, leading to dependance on gymnastics with Flats. The 294 backlit architecture does not lend itself to even substrate cooling, producing gradients when used in traditional long sub imaging. The 294 is fine for high frame rate video, and EAA use. By comparison the 1600 does not require Flats at all, I never found them necessary.
Reply With Quote
  #3  
Old 28-09-2020, 09:37 AM
Camelopardalis's Avatar
Camelopardalis (Dunk)
Drifting from the pole

Camelopardalis is offline
 
Join Date: Feb 2013
Location: Brisbane
Posts: 5,425
That’s not microlensing on the 1600. It’s much more obvious than that...it’s a square grid pattern. If you point it at Alnitak or another similarly bright star it’ll become very obvious after you’ve integrated a few subs.

I also have an Esprit 100 and 1600 and the only image I’ve felt the microlensing effect has ruined an image is around the Horsehead nebula, with above mentioned Star featuring heavily :LOL:

You’re most likely seeing something actually causing diffraction, like the leaf of a tree or something else funky.
Reply With Quote
  #4  
Old 28-09-2020, 05:22 PM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
I've grabbed a cropped sub from the blue filter it shows the grid a bit better, it's definitely not an obstruction, the star probably isn't bright enough to really show it. I can also agree that the 294mc is not without its issues but with the 1600 sensor being discontinued it will soon be the only new option. Is there a way of using something like a layer mask to fix microlensing? I've had some success with the clone tool but I admit my photoshop/gimp experience is fairly limited.
Attached Thumbnails
Click for full-size image (Microlensing.jpg)
84.5 KB69 views
Reply With Quote
  #5  
Old 28-09-2020, 05:34 PM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline
 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
David,
Why do you say the ASI 1600 is being discontinued??
I use it regularly for solar imaging, with no issues.
Reply With Quote
  #6  
Old 28-09-2020, 06:34 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
+1 That's not microlensing. These are internal reflections and/or diffraction somewhere in your imaging train.

This is microlensing on a QHY9 mono sensor (KAF8300) taken with an FSQ106N that has no diffraction spikes whatsoever.
Attached Thumbnails
Click for full-size image (IC2948_SiiHaOiii_B_100.jpg)
128.9 KB73 views
Reply With Quote
  #7  
Old 28-09-2020, 06:50 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by sunslayr View Post
I've grabbed a cropped sub from the blue filter it shows the grid a bit better
If I had to guess I'd say this is an image of the sensor made by the light bouncing from it to the back of a filter or piece of glass close to it.
Reply With Quote
  #8  
Old 28-09-2020, 10:25 PM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
Ok now I'm confused, Is in not the reflections of the microlens array being reflected back due to the lack of AR coating on the sensor cover glass? Or are you saying the sensor itself is being reflected back from my filters and/or AR Cover glass on the front of the camera. As far as I know my Astrodon filters are AR coated both sides? Also If it was the filter, corrector or something else would the reflections not be further from the star? Each circle is no more than 65px apart.

I guess I just assumed because it looks exactly like what I'd expect with all those circles.

http://hamamatsu.magnet.fsu.edu/arti...photodiode.jpg

Ken the Panasonic sensor AMN34230 used in the 1600mm is listed as EOL. I'm not sure how much stock ZWO and QHY have left however.

Last edited by sunslayr; 28-09-2020 at 10:50 PM.
Reply With Quote
  #9  
Old 29-09-2020, 12:33 AM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline
 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
David,
Thanks for the update on the ASI 1600 sensor......what do I say? It worked very well for me. RIP
Reply With Quote
  #10  
Old 29-09-2020, 10:40 AM
Camelopardalis's Avatar
Camelopardalis (Dunk)
Drifting from the pole

Camelopardalis is offline
 
Join Date: Feb 2013
Location: Brisbane
Posts: 5,425
Quote:
Originally Posted by sunslayr View Post
Ok now I'm confused, Is in not the reflections of the microlens array being reflected back due to the lack of AR coating on the sensor cover glass? Or are you saying the sensor itself is being reflected back from my filters and/or AR Cover glass on the front of the camera. As far as I know my Astrodon filters are AR coated both sides? Also If it was the filter, corrector or something else would the reflections not be further from the star? Each circle is no more than 65px apart.

I guess I just assumed because it looks exactly like what I'd expect with all those circles.
The grid pattern in your blue channel image is the microlens grid pattern, the larger and more obvious circular pattern is something else.

I might have a go when Orion gets high enough over the neighbours, as I've never noticed the grid pattern on those stars you're seeing it on (and I do go looking for it!)
Reply With Quote
  #11  
Old 29-09-2020, 10:56 AM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
Ahh I see, yeah I was only talking about the grid. Not sure about the circular one. Now that I look at it I see it wasn't very clear. The circular one is a mystery to me to to be honest, this is the only image I've encountered it. Maybe the grid is not quite overlapping and making a circle
Reply With Quote
  #12  
Old 30-09-2020, 09:36 AM
Camelopardalis's Avatar
Camelopardalis (Dunk)
Drifting from the pole

Camelopardalis is offline
 
Join Date: Feb 2013
Location: Brisbane
Posts: 5,425
yeah could be nothing ventured nothing gained!

TBH I didn’t notice that in your image when you raised it, it was the bright circular outer ring that stood out.
Reply With Quote
  #13  
Old 30-09-2020, 12:02 PM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
Been doing a little research and learned some pretty cool things. First of all when I examined the channels separately a found the grid was larger and more spread out in the red channel while it was small and tight in the blue. I thought to myself if that corresponds to the wavelength of light, maybe I can use it to calculate the thickness of the cmos cover glass?

Turns out the person who runs Geoastro has done most of the work for me. Unfortunately they did not provide their spreadsheet so I had make a copy for myself to make the calculations a little easier. I will provide a link for anyone who would like to play around with it themselves. Using it I calculated an average distance of 1.3mm, which sounds about right to me. It also appears I was correct in my assumption that an uneven overlap results in a round artifact in the final image.
Attached Thumbnails
Click for full-size image (Green Channel.jpg)
133.5 KB23 views
Click for full-size image (Blue Channel.jpg)
127.6 KB24 views
Click for full-size image (Red Channel.jpg)
110.9 KB23 views
Reply With Quote
  #14  
Old 30-09-2020, 02:20 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
If you push any system on a bright star you'll get ghosts. Here's my CN-212 with just mirrors in the imaging train but for the camera CCD glass.
That's alpha crux.
Attached Thumbnails
Click for full-size image (ghosts.jpg)
198.8 KB42 views
Reply With Quote
  #15  
Old 30-09-2020, 02:39 PM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline
 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
David, I like the analysis - it appeals to me being a spectroscopist.


I have also had to look at the sensor cover plate as a source of resonance banding in the spectrum. The effect we see is very similar to that produced by an F-P etalon filter.


http://astrosurf.com/aras/fringing/opus/
http://www.astrosurf.com/aras/fringi...ter/ripple.htm


I experienced this effect while testing a high resolution spectroheliograph.
The reason for mentioning all this related testing, is to remind you that the sensor cover plates were all measured to be around 0.3 to 0.5mm think.
None were in the range you seem to calculate.
I need to double check my data files, but from memory the cover plate in the ASI 1600 is 0.5mm thick.
Attached Thumbnails
Click for full-size image (ASI174_CaK_banding.JPG)
33.9 KB15 views
Click for full-size image (ASI174_Na_banding.JPG)
48.5 KB14 views
Click for full-size image (ASI174_ha_banding.JPG)
45.9 KB11 views
Click for full-size image (AZOM_14009_fringing.JPG)
38.9 KB17 views
Reply With Quote
  #16  
Old 30-09-2020, 04:09 PM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
Thanks for the input Ken. I really don't claim to be an optical expert it's quite possible I'm wrong I wasn't able to find the data on the spec sheet so I just googled cmos cover glass thickness and got a result of about 1mm. I think I might just blame the data, its not a single wavelength so my results say ~=1.3mm +-1mm
Reply With Quote
  #17  
Old 30-09-2020, 04:52 PM
Merlin66's Avatar
Merlin66 (Ken)
Registered User

Merlin66 is offline
 
Join Date: Oct 2005
Location: Junortoun Vic
Posts: 8,904
The “geoastro” ghosts were generated between the sensor and a remote (20mm) filter element.
I think this could be a different process from the narrow band etalon effects we see in Spectra.
Reply With Quote
  #18  
Old 01-10-2020, 09:21 AM
Camelopardalis's Avatar
Camelopardalis (Dunk)
Drifting from the pole

Camelopardalis is offline
 
Join Date: Feb 2013
Location: Brisbane
Posts: 5,425
Good work

David, are your three images above R G and B channels (in that order) ?
Reply With Quote
  #19  
Old 01-10-2020, 09:46 AM
sunslayr (David)
Registered User

sunslayr is offline
 
Join Date: Nov 2018
Location: Perth
Posts: 209
Quote:
Originally Posted by Camelopardalis View Post
Good work

David, are your three images above R G and B channels (in that order) ?
I think they are GBR, I think if you hover your mouse over them it should tell you which is which. I Probably should have paid more attention while uploading.
Reply With Quote
  #20  
Old 01-10-2020, 10:19 AM
Stonius's Avatar
Stonius (Markus)
Registered User

Stonius is offline
 
Join Date: Mar 2015
Location: Melbourne
Posts: 1,494
Dunk and Marc - it seems there is a difference of opinion over what microlensing actually is.


I always thought it was precisely what we see above - a reflection of the microlens array from the back of the sensor window on particularly bright stars (Alnitak being notorious). Also, Marc - I can't see anything particularly wrong with the image you posted - where is the microlensing you refer to in that image?


Sorry for being a dunce - maybe I've misunderstood this all along?


Cheers


Markus
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 05:53 PM.

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