Go Back   IceInSpace > Images > Deep Space

Reply
 
Thread Tools Rate Thread
  #41  
Old 09-06-2019, 10:40 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 6,473
Quote:
Originally Posted by Sunfish View Post
Astonishing really for an earth bound image. Maybe a minor point but keeping the stars in a natural way in addition to the detail of nebula is superb.
Thanks Ray. I've just uploaded a very high quality .jpg version to the page with the same URL
to allow the pixel peepers (and, guilty as charged, I'm one of them) to have a better look with decidedly less .jpg artifacts.

Sorry not 4k...I don't do 4k for the web.. (Marcus will likely be crestfallen) , but no jagged .jpg stars.
Reply With Quote
  #42  
Old 10-06-2019, 12:22 PM
Atmos's Avatar
Atmos (Colin)
Ultimate Noob

Atmos is offline
 
Join Date: Aug 2011
Location: Melbourne
Posts: 6,082
There have been a few topics over the years on CN in regards to image scale, contrast transfer (MTF), pixel size and the like. Although some of the mathematics in the discussions went over my head I could understand enough of it.

In astrophotography there are two types of sources, point (stars) and non-point (everything else!). As apertures increase so does light intensity from stars directly proportionally to the aperture increase. This is aperture flux and is spread over however many pixels your FWHM is.
Non-stellar objects like galaxies and nebulae are a function of pixel size and focal ratio. With this were flux per square arcsec of sky is important.

What this means is that stars saturate slower in smaller refractors than larger reflections BUT both being able to image just as deep into a nebula with the same integration time. This is what makes wide field astro graphs (FSQs, flat field APOs, photographic lens') so good at what they do. They can image bright stars, fainter stars, galaxies and nebulosity in one exposure easier than a larger aperture.

So why don't the 80-130mm refractors or even 8-12" reflectors generally come as sharp as what Peter has posted? Seeing conditions is definitely a big part of that. Mostly though, it's aperture. What aperture allows is for you to image at a higher scale while maintaining SNR and therefore contrast. Contrast by definition is how well defined brightness differences are at small and large scales.

Take an 8" F/4.25 with ASI183 (close to yours Lee) and a 16" F/8 and PL16803.
Both image at 0.58"/pixel but as we're mostly talking about non-stellar objects (contrast in the nebulosity) we only care about pixel size and focal ratio.
2.4^2/9^2 = 14x more light per pixel
8^2/4.25^2 = 3.54x less light concentration

The larger aperture gets 3.95x more flux per square arcsec because the 16" is sucking in 4x the amount of photons as the 8" AND they're imaging at the same image scale.
Replace the ASI183 with a KAF-8300 and its 5.4 micron pixels and the situation changes where the smaller aperture ends up with 27.4% higher SNR with the same integration BUT it's now doing so at 1.31"/pixel. What this achieves is stronger signal on the fainter structures further out from the core of M42 and better contrast on the large scale structures BUT without the resolution to capture those small scale structures anymore.
Reply With Quote
  #43  
Old 25-06-2019, 09:42 AM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 6,473
Quote:
Originally Posted by Atmos View Post
....

So why don't the 80-130mm refractors or even 8-12" reflectors generally come as sharp as what Peter has posted? Seeing conditions is definitely a big part of that. Mostly though, it's aperture. What aperture allows is for you to image at a higher scale while maintaining SNR and therefore contrast. Contrast by definition is how well defined brightness differences are at small and large scales."....
Thanks for your analysis .....also as a post script...I guess it was not too shabby as the image picked up a gong at this year's CWAS/Malin awards
Reply With Quote
  #44  
Old 25-06-2019, 10:38 AM
Atmos's Avatar
Atmos (Colin)
Ultimate Noob

Atmos is offline
 
Join Date: Aug 2011
Location: Melbourne
Posts: 6,082
Congratulations

Something else that Roland brought up a few years ago that surprised me was that seeing and optical errors are additive. I’d always imaged that as long as optical quality was below 3x seeing that it would be swamped by seeing error but if take it as additive then optical quality helps reduce seeing error to some degree.

For most people a Celestron Edge14 doesn’t need to have better optical performance than 15-20 microns on-axis for local seeing but apparently if that’s dropped down to 5 microns on-axis, even though WELL below seeing for most of us, helps cut through the seeing to some degree.
Reply With Quote
  #45  
Old 25-06-2019, 12:54 PM
astroron's Avatar
astroron (Ron)
Supernova Searcher

astroron is offline
 
Join Date: Mar 2005
Location: Cambroon Queensland Australia
Posts: 8,798
Not much that I can add to all the other comments,
except to say"Absolutely Fabulous"
Thanks for posting Peter.
Cheers
Reply With Quote
  #46  
Old 25-06-2019, 03:44 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 6,473
Quote:
Originally Posted by astroron View Post
Not much that I can add to all the other comments,
except to say"Absolutely Fabulous"
Thanks for posting Peter.
Cheers
Thanks. My pleasure.

Quote:
Originally Posted by Atmos View Post
Congratulations

Something else that Roland brought up a few years ago that surprised me was that seeing and optical errors are additive....
Ta.

Indeed, stands to reason, to use a cup of water analogy if the optic is barely diffraction limited (i.e.full to the brim) , then *any* seeing perturbation will cause light spill. If the cup is a bit deeper, the things can slosh about a bit before the cup spills.
Reply With Quote
  #47  
Old 25-06-2019, 06:40 PM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,149
Congrats on the gong. I thought it would.

Greg.
Reply With Quote
  #48  
Old 25-06-2019, 10:35 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 6,473
Quote:
Originally Posted by gregbradley View Post
Congrats on the gong. I thought it would.

Greg.
Ta...actually got two, that and a wide field, but won't know (as usual) how they rated until the awards night next month....many great imagers in Oz these days, hence my expectations are modest..
Reply With Quote
  #49  
Old 29-06-2019, 09:23 AM
gregbradley's Avatar
gregbradley
Registered User

gregbradley is offline
 
Join Date: Feb 2006
Location: Sydney
Posts: 15,149
Quote:
Originally Posted by Peter Ward View Post
Ta...actually got two, that and a wide field, but won't know (as usual) how they rated until the awards night next month....many great imagers in Oz these days, hence my expectations are modest..
The 60Da image right? As soon as I saw it I thought that's going to get that category.

Greg.
Reply With Quote
  #50  
Old 29-06-2019, 07:39 PM
Peter Ward's Avatar
Peter Ward
Galaxy hitchhiking guide

Peter Ward is offline
 
Join Date: Dec 2007
Location: The Shire
Posts: 6,473
Quote:
Originally Posted by gregbradley View Post
The 60Da image right? As soon as I saw it I thought that's going to get that category.

Greg.
Sorry Greg, missed your post. Yes, a version of that pano got a nod...but
best guess is an HM.....but we'll all find out on the 19th!

It was not that hard to do. Despite passing clouds, the skies were remarkably dark (passing clouds were darker than the sky) I just clicked away.

No guiding at all (used the starlapse) also have to say Sigma's 105mm F1.4...which has a 90mm objective...just sucked up the photons and is amazing bang for buck.
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 12:39 AM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
Celestron Australia
Advertisement
Meade Australia
Advertisement
NexDome Observatories
Advertisement
Lunatico Astronomical
Advertisement
Bintel
Advertisement
SkyWatcher Australia
Advertisement
OzScopes Authorised Dealer
Advertisement
Astronomy and Electronics Centre
Advertisement