#21  
Old 12-08-2020, 06:17 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 17,877
A picture is worth a thousand words:

ASI183mm Pro 2.4 micron pixels on AP RHA 305 F3.8 in semi rural skies:

https://pbase.com/gregbradley/image/170949826 ASI183mm Pro

FLI Microline 16200 (6 micron pixels at a dark site):

https://pbase.com/gregbradley/image/170949827 CDK17 ML16

As you can see the 183mm image is much the same brightness despite being taken on a 305mm scope in semi rural skies versus a 435mm scope at a dark site. The CDK image should be much brighter than the 183mm but its not.

This matching pixels to optics, in my opinion, is a very limited theory and there are other factors just as important like QE, read noise, dark current, dark skies, seeing. The effects of mismatched pixels don't seem to me to be that great in reasonable seeing.

Greg.

Last edited by gregbradley; 12-08-2020 at 06:27 PM.
Reply With Quote
  #22  
Old 12-08-2020, 08:45 PM
Slawomir's Avatar
Slawomir (Suavi)
Registered User

Slawomir is offline
 
Join Date: Sep 2014
Location: North Queensland
Posts: 3,240
Greg - in this scenario it would be much more fitting to compare SNR from your both cameras when operating on the same scope (same length of total exposure), as Lewis is contemplating replacing his KAF8300 with ASI183 while keeping the same scope.

I believe is you stick ASI183 onto your CDK17 you will see a much weaker signal than from the KAF16200. Alternatively, if you attach KAF16200 to your Honders I suspect the SNR will be stronger than with the ASI183-Honders combo for the same length of total exposure and for the same object.
Reply With Quote
  #23  
Old 13-08-2020, 02:54 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Decided to continue on with the ST-8300C and the SXVR-H9C. Both aren't tiny pixels, nor are they enormous, but I'll just try my best.
Reply With Quote
  #24  
Old 13-08-2020, 03:14 PM
multiweb's Avatar
multiweb (Marc)
ze frogginator

multiweb is offline
 
Join Date: Oct 2007
Location: Sydney
Posts: 22,060
Quote:
Originally Posted by LewisM View Post
Decided to continue on with the ST-8300C and the SXVR-H9C. Both aren't tiny pixels, nor are they enormous, but I'll just try my best.
Debayer in PI. It's smart enough to drizzle off the original bayer matrix. Shoot shorter subs but more of them.
Attached Thumbnails
Click for full-size image (PI_drizzle.gif)
178.5 KB154 views
Reply With Quote
  #25  
Old 13-08-2020, 03:52 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Quote:
Originally Posted by multiweb View Post
Debayer in PI. It's smart enough to drizzle off the original bayer matrix. Shoot shorter subs but more of them.

Agreed Marc - last time I imaged, I did that - dither, debayer, drizzle integration etc. And that was using a 9 micron sensor camera and no horrific results - well, no more horrific than my usual mess.


And the new EZ Suite really makes my mess just that little bit tidier.
Reply With Quote
  #26  
Old 13-08-2020, 08:11 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 17,877
Quote:
Originally Posted by Slawomir View Post
Greg - in this scenario it would be much more fitting to compare SNR from your both cameras when operating on the same scope (same length of total exposure), as Lewis is contemplating replacing his KAF8300 with ASI183 while keeping the same scope.

I believe is you stick ASI183 onto your CDK17 you will see a much weaker signal than from the KAF16200. Alternatively, if you attach KAF16200 to your Honders I suspect the SNR will be stronger than with the ASI183-Honders combo for the same length of total exposure and for the same object.
Yeah I wanted to do that but I don't think I have the same data from both cameras on the same scope. I'll look again.

Greg.
Reply With Quote
  #27  
Old 14-08-2020, 06:15 AM
codemonkey's Avatar
codemonkey (Lee)
Lee "Wormsy" Borsboom

codemonkey is offline
 
Join Date: Jul 2013
Location: Kilcoy, QLD
Posts: 2,058
The small pixels might give you sharper results, they'll almost certainly get you rounder, less blocky stars... I agree with what's already been said though, I'd try dither + drizzle first which will definitely round up those stars.

What's your typical guide error (total RMS in arcseconds)? What do you use for autofocus (hardware and software)?
Reply With Quote
  #28  
Old 14-08-2020, 04:33 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Quote:
Originally Posted by codemonkey View Post
The small pixels might give you sharper results, they'll almost certainly get you rounder, less blocky stars... I agree with what's already been said though, I'd try dither + drizzle first which will definitely round up those stars.

What's your typical guide error (total RMS in arcseconds)? What do you use for autofocus (hardware and software)?

Get perfectly round stars. I do dither (up to 5 pixels) and drizzle integrate in PI. Here's an image from last time I imaged last year https://www.astrobin.com/full/mv7lg0/0/


Guide error.... errr.... don't you recall my guide error...essentially, well, none...


Autofocus? No way Jose! Bahtinov and Eyeball Mk.1 for me (zoomed in 300% in MaxIM 6)


Here's my guide error...yeah its in pixels, but I don't use PHD...MaxIM does a FANTASTIC job. Suavi, it is STILL not guiding on a hot pixel (another shot when there was a minor burp here: http://www.iceinspace.com.au/forum/a...e.php?a=225766)
Attached Thumbnails
Click for full-size image (IMG_3450.jpg)
110.4 KB174 views
Click for full-size image (IMG_3448.jpg)
95.9 KB178 views
Reply With Quote
  #29  
Old 14-08-2020, 05:40 PM
Slawomir's Avatar
Slawomir (Suavi)
Registered User

Slawomir is offline
 
Join Date: Sep 2014
Location: North Queensland
Posts: 3,240
Fantastically flat guide graph Lewis. I presume you are still binning Lodestar 2x2 on a 150mm FL guide-scope

On a more serious topic - at about 2.5" pp you would most likely recover some resolution by drizzling sufficient number of dithered subs.
Reply With Quote
  #30  
Old 14-08-2020, 06:20 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Quote:
Originally Posted by Slawomir View Post
Fantastically flat guide graph Lewis. I presume you are still binning Lodestar 2x2 on a 150mm FL guide-scope

On a more serious topic - at about 2.5" pp you would most likely recover some resolution by drizzling sufficient number of dithered subs.

Drizzling certainly does. Next time I actually get to image - maybe next year at this rate - I'll be doing it all the time.
Reply With Quote
  #31  
Old 15-08-2020, 04:15 PM
codemonkey's Avatar
codemonkey (Lee)
Lee "Wormsy" Borsboom

codemonkey is offline
 
Join Date: Jul 2013
Location: Kilcoy, QLD
Posts: 2,058
Quote:
Originally Posted by LewisM View Post
Get perfectly round stars. I do dither (up to 5 pixels) and drizzle integrate in PI. Here's an image from last time I imaged last year https://www.astrobin.com/full/mv7lg0/0/


Guide error.... errr.... don't you recall my guide error...essentially, well, none...


Autofocus? No way Jose! Bahtinov and Eyeball Mk.1 for me (zoomed in 300% in MaxIM 6)


Here's my guide error...yeah its in pixels, but I don't use PHD...MaxIM does a FANTASTIC job. Suavi, it is STILL not guiding on a hot pixel (another shot when there was a minor burp here: http://www.iceinspace.com.au/forum/a...e.php?a=225766)
lol I had forgotten about your hot pixel guiding.

I asked about focusing and guiding because in my experience these are critical to get the most out of your scope and if there was any question there, I'd be focusing (pun intended) on those before even thinking about a different camera.

Maybe you're an expert turner of focus knobs, but personally I could never manually focus as well as a properly-configured auto focus routine can do. In addition to that, if your stars aren't looking like little squares at 2.48"/px with a Tak, I'd be guessing you're probably not getting the best focus that you could. You're too undersampled for them to look perfectly round (in single subs, prior to drizzle integration).

As for guiding... it's common to assume that if your stars are round, your guiding is fine, but that only suggests that both axes are equally good (or bad). I can very easily misconfigure guiding to significantly increase my FWHM while still getting round stars. In my experience, solid guiding is the next most important thing.

If there's any question on either guiding or focusing, I'd encourage you to to investigate those first.
Reply With Quote
  #32  
Old 16-08-2020, 08:43 AM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 3,342
Regards drizzle versus smaller pixels. My old ASI294 on my 80mm is just about bang on 2 arcsec per pixel, I recently used drizzle in APP on a set of subs I had and ran it a couple of times at different settings to work out where the noise started to become objectionable. First light with my ASI2600 (3.7 versus 4.63um pixels to make it 1.6 or so arcsec per pixel) was of the same target, unguided and with spacing still to be sorted, but to me the star profiles looked at least as smooth with 20 subs and all the tracking and spacing errors as the drizzled stack of 100 subs.

I suppose it says you can get a result both ways.
Reply With Quote
  #33  
Old 16-08-2020, 09:25 AM
Slawomir's Avatar
Slawomir (Suavi)
Registered User

Slawomir is offline
 
Join Date: Sep 2014
Location: North Queensland
Posts: 3,240
Paul - I believe 3.7micron pixels are at about diffraction limit for your 80mm, so stars should be round in the subs already, as opposed to 4.6micron pixels that, with good guiding, should give somehow blocky stars. Wondering if FDHM got better (smaller) with the new camera.
Reply With Quote
  #34  
Old 16-08-2020, 12:47 PM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 3,342
I am not paying any attention to image stats yet, not until it is properly set up spacing wise and guided. Subjectively the stars look nicer already with native resolution instead of recovering it via drizzle on more undersampled data.
Reply With Quote
  #35  
Old 17-08-2020, 10:01 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 The_bluester View Post
Regards drizzle versus smaller pixels. My old ASI294 on my 80mm is just about bang on 2 arcsec per pixel, I recently used drizzle in APP on a set of subs I had and ran it a couple of times at different settings to work out where the noise started to become objectionable. First light with my ASI2600 (3.7 versus 4.63um pixels to make it 1.6 or so arcsec per pixel) was of the same target, unguided and with spacing still to be sorted, but to me the star profiles looked at least as smooth with 20 subs and all the tracking and spacing errors as the drizzled stack of 100 subs.

I suppose it says you can get a result both ways.
Both ways are increasing your sampling, which is why both work
Reply With Quote
  #36  
Old 17-08-2020, 12:31 PM
The_bluester's Avatar
The_bluester (Paul)
Registered User

The_bluester is offline
 
Join Date: Feb 2011
Location: Kilmore, Australia
Posts: 3,342
Yep, just now having done it both ways I reckon my preference is for good sampling to begin with rather than retrieving more data via drizzle, the noise difference is noticeable, at least to me.


The downside being that the better sampling increases data storage requirements and processing times!
Reply With Quote
  #37  
Old 17-08-2020, 12:39 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
Quote:
Originally Posted by codemonkey View Post
lol I had forgotten about your hot pixel guiding.

I asked about focusing and guiding because in my experience these are critical to get the most out of your scope and if there was any question there, I'd be focusing (pun intended) on those before even thinking about a different camera.

Maybe you're an expert turner of focus knobs, but personally I could never manually focus as well as a properly-configured auto focus routine can do. In addition to that, if your stars aren't looking like little squares at 2.48"/px with a Tak, I'd be guessing you're probably not getting the best focus that you could. You're too undersampled for them to look perfectly round (in single subs, prior to drizzle integration).

As for guiding... it's common to assume that if your stars are round, your guiding is fine, but that only suggests that both axes are equally good (or bad). I can very easily misconfigure guiding to significantly increase my FWHM while still getting round stars. In my experience, solid guiding is the next most important thing.

If there's any question on either guiding or focusing, I'd encourage you to to investigate those first.
Zero issues with guiding or mount. Maybe my focus isn’t exact but I am not a fan of adding yet more bits on. Been there with AF before, didn’t float my boat - I like actually being out with my scope doing stuff. Automated to me takes away most of the fun of astronomy, and besides, not in it for image glory and fame.

Only reason I was considering a small pixel cam is because of my typical low total time data sets. I am happy with my round stars as is, and if only slightly under sampled given our typical good to excellent seeing here, I can live with it. Better than being over sampled

As Marc said, make the best of what you have.
Reply With Quote
  #38  
Old 17-08-2020, 01:01 PM
DavidTrap's Avatar
DavidTrap (David)
Really just a beginner

DavidTrap is offline
 
Join Date: Jun 2009
Location: Brisbane
Posts: 3,032
Have you tried putting the y-axis of your guiding graph on arcsec of error rather than pixels - lets compare apples with apples?

DT
Reply With Quote
  #39  
Old 17-08-2020, 01:08 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
David doesn’t mean anything to me honestly and I don’t use PHD. So long as it works I don’t chase numbers.

My graph in MaxIM in arcsecond isnt much different. It’s not the mount or guiding I am even remotely interested in, it was simply can I maybe get the stars etc sharper given all else being to my satisfaction.
Reply With Quote
  #40  
Old 17-08-2020, 01:15 PM
LewisM's Avatar
LewisM
Novichok test rabbit

LewisM is offline
 
Join Date: Aug 2012
Location: Somewhere in the cosmos...
Posts: 10,388
PS- I have done 20, 45 and 60 min single subs with this same rig with zero trailing, same star shapes. Also did the same with an FSQ106ED
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 08:58 AM.

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