#1  
Old 12-03-2008, 05:33 AM
skwinty's Avatar
skwinty (Steve)
E pur si muove

skwinty is offline
 
Join Date: Dec 2007
Location: Cape Town
Posts: 494
More noise from a blunt tool

Herewith another pdf as promised to Baz and Fred.
see deep space and Centaurus trifid thread.
Regards
Steve

Last edited by skwinty; 14-03-2008 at 05:11 PM.
Reply With Quote
  #2  
Old 13-03-2008, 09:11 AM
Geoff45's Avatar
Geoff45 (Geoff)
PI rules

Geoff45 is offline
 
Join Date: Jul 2006
Location: Sydney
Posts: 2,631
Interesting document.

Thanks, I've printed it off.
Geoff
Reply With Quote
  #3  
Old 13-03-2008, 09:19 AM
RB's Avatar
RB (Andrew)
Moderator

RB is offline
 
Join Date: Aug 2005
Posts: 25,732
Some great info there.

Reply With Quote
  #4  
Old 13-03-2008, 04:08 PM
Bassnut's Avatar
Bassnut (Fred)
Narrowfield rules!

Bassnut is offline
 
Join Date: Nov 2006
Location: Torquay
Posts: 5,064
Thanks Steve, very clear and easy to read.
Reply With Quote
  #5  
Old 13-03-2008, 04:13 PM
skwinty's Avatar
skwinty (Steve)
E pur si muove

skwinty is offline
 
Join Date: Dec 2007
Location: Cape Town
Posts: 494
Thanks all for the comments.
Will do more of these as I progress through the learning curve.
Regards
Steve
Reply With Quote
  #6  
Old 13-03-2008, 04:32 PM
Bassnut's Avatar
Bassnut (Fred)
Narrowfield rules!

Bassnut is offline
 
Join Date: Nov 2006
Location: Torquay
Posts: 5,064
Steve, I might say though, the statement "Dark 5 times the total image integration time" just isnt viable these days, not even 2 times.

I sometimes and many imagers now image (especially NB) to a total of 5 or more hrs per filter. A 25 or even 10 hr dark is just rediculous. I have found 10 stacked dark subs at the same exposure as the image subs is about as far as you need to go (youd be hard pressed to see much difference in more than 3 dark subs), regardless of total image time. The noise reduction acheived in the dark past 10 subs fast becomes a case of diminishing returns, cant see the point in much more than about 10 subs.
Reply With Quote
  #7  
Old 13-03-2008, 05:24 PM
skwinty's Avatar
skwinty (Steve)
E pur si muove

skwinty is offline
 
Join Date: Dec 2007
Location: Cape Town
Posts: 494
Hi Fred
I agree. A 1 hour exposure and a 5 hour dark is excessive.
I suppose it depends on the amount of noise obsession you suffer from.
If you look at the icnr of the latest DSLR's then if you do a 30 min exposure the icnr will do a 30 min dark. I see that as a minimum.
I do also understand the point of dark frames exceeding the exposure time as the thermal electron generation varies from about .001 electrons/pixel/sec to about 30 electrons/pixel/sec depending on type of sensor and whether its cooled or not.
I think however that when you are shooting very faint DSO's where other noise dominates and buries the signal then you might be forced to go to these extremes.
My approach to this, as i use track and stack with short exposures is , if I shoot 60 second subs then I will do a few 120 to 300 sec darks, combine these darks into a master dark and use the master.
I will investigate this issue futher and post further comments as the rationale and math behind this approach is quite comprehensive.
Regards
Steve
Reply With Quote
  #8  
Old 13-03-2008, 05:40 PM
Bassnut's Avatar
Bassnut (Fred)
Narrowfield rules!

Bassnut is offline
 
Join Date: Nov 2006
Location: Torquay
Posts: 5,064
Steve, I really am not sure why you would expose 120-300 sec darks (or do you mean 60 sec stacked subs) for a 60 sec image sub. Hot pixels in long exposure darks, if stacked sum for example, would not match hot pixels in the image subs. Stacking software will adapt to different exposure times, but I dont get the point, why not stack like for like exposure times, this would reduce noise and leave hot pixels at the correct level.
Reply With Quote
  #9  
Old 13-03-2008, 05:51 PM
EzyStyles's Avatar
EzyStyles (Eric)
I HATE COMA!

EzyStyles is offline
 
Join Date: Jan 2006
Location: Melbourne, Victoria
Posts: 3,208
Thanks for the .pdf. ALthough i have to admit i shoot "ALL" my images in .jpg so sue me

Now go out there Steve and take some shots. will be good to see some unknown objects from your sky.
Reply With Quote
  #10  
Old 13-03-2008, 05:58 PM
Bassnut's Avatar
Bassnut (Fred)
Narrowfield rules!

Bassnut is offline
 
Join Date: Nov 2006
Location: Torquay
Posts: 5,064
Holly cow Eric, you serious, Im stunned, amazing results with lowly JPEG then, cant believe it
Reply With Quote
  #11  
Old 13-03-2008, 06:07 PM
iceman's Avatar
iceman (Mike)
Sir Post a Lot!

iceman is offline
 
Join Date: Sep 2004
Location: Gosford, NSW, Australia
Posts: 36,760
Eric!? What!? jpeg? Shoot RAW you lazy so and so! Your images will improve even more!
Reply With Quote
  #12  
Old 13-03-2008, 06:11 PM
EzyStyles's Avatar
EzyStyles (Eric)
I HATE COMA!

EzyStyles is offline
 
Join Date: Jan 2006
Location: Melbourne, Victoria
Posts: 3,208
LOL you guys have no idea how many times i get flamed for shooting my images in RAW. ... i guess laziness plays a huge part and how easy it is to play with .jpg files than RAW. yess im guilty now and will shoot in RAW when i get a new camera
Reply With Quote
  #13  
Old 13-03-2008, 08:19 PM
skwinty's Avatar
skwinty (Steve)
E pur si muove

skwinty is offline
 
Join Date: Dec 2007
Location: Cape Town
Posts: 494
Hi Fred
Sorry took so long to reply but had to rush off to the nuclear power station down the road.
I work for Nuclear Consultants International.
No major problem at the power station. I like to call myself an Unclear Engineer.
Will read some more tonight and post some tomorrow.
Regards
Steve
Reply With Quote
  #14  
Old 13-03-2008, 09:35 PM
Zuts
Registered User

Zuts is offline
 
Join Date: Mar 2007
Location: sydney
Posts: 1,830
Hi,

I think when they say take 5 times as long darks as lights they dont mean take one dark 5 times as long they mean take 5 darks as long as the light.

If you go longer then you will get a different hot pixel response and would be removing good data because the dark would have many many more hot pixels.

You stack images to average noise and you should also stack darks to average noise as well.

If you go longer DSS for example will try and scale but this is not optimal.

Paul
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 10:09 PM.

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