Go Back   IceInSpace > Equipment > Astrophotography and Imaging Equipment and Discussions

Reply
 
Thread Tools Rate Thread
  #1  
Old 27-02-2006, 12:31 PM
Vermin's Avatar
Vermin (Tom)
Cloud dodger

Vermin is offline
 
Join Date: Dec 2004
Location: Hobart
Posts: 584
Selecting exposure time(s) and Canon EOS data

I'm wondering if there is a reference for selecting exposure times and film speeds when doing DSLR DSO astrophotography.

How do you select the individual exposure lengths and number of exposures based on the surface brightness of the DSO and camera ISO setting?

I realise the noise benefits of keeping the ISO setting as low as possible to reduce noise, but that's about it.

Thanks,

Tom.
Reply With Quote
  #2  
Old 27-02-2006, 12:36 PM
[1ponders]'s Avatar
[1ponders] (Paul)
Retired, damn no pension

[1ponders] is offline
 
Join Date: Nov 2004
Location: Obi Obi, Qld
Posts: 18,778
There are formula around to help Tom, but I mainly use the tables in the back of Michael Covingtons book.
Reply With Quote
  #3  
Old 27-02-2006, 12:39 PM
Striker's Avatar
Striker (Tony)
Whats visual Astronomy

Striker is offline
 
Join Date: Dec 2004
Location: Brisbane
Posts: 5,062
It's trail and error with me anyway....

It's going to depend on ISO speed, focal ratio, aperture and skyglow plus other factors.

A good way to start is with ISO 800 - 1600 and do a 1 minute exposure..then 2 minute then 3 then 4 and so on...you will soon see if the image has been taken over with too much skyglow or is over exposed.

I dont think anyone could tell you exactly what timed exposures to take....you will also have to take into account what your imaging...too many factors for me to work out....so just do what I mentioned above...experiment...you will soon know approx what times you need to set your exposure length.

Hope this helps a little
Reply With Quote
  #4  
Old 27-02-2006, 12:49 PM
RB's Avatar
RB (Andrew)
Moderator

RB is offline
 
Join Date: Aug 2005
Posts: 21,995
I agree with Tony and Paul.
These days with the advent of DSLR's it's easier to do trial and error work.
I take my hat off to the guys who did such beautiful work on DSOs using film.
The reason I got back into astro is because DSLRs make it easier to check what you've just taken.

I'd recommend using ISO800 over the ISO1600 whenever possible.
ALWAYS shoot in RAW (and jpg at the same time if your camera allows this) because you can quickly see you jpg version when checking on the main computer.

1 to 2 min should give you a good indication on a starting point.
Reply With Quote
  #5  
Old 27-02-2006, 03:12 PM
Vermin's Avatar
Vermin (Tom)
Cloud dodger

Vermin is offline
 
Join Date: Dec 2004
Location: Hobart
Posts: 584
I agree a fair bit of experimentation is required but the tables Paul mentioned were the sort of ball park figure I was looking for to base this experimentation on.

As for shooting using ISO800 and above, until today I would have disagreed, unless you were using a Canon 5D camera.

A lot of the 350D and 20D photos I've seen are slightly marred by excessive noise (in my opinion). I certainly mean no disrespect to the photographers of these otherwise excellent images, I only hope I will be able to do half as well.

I thought using a lower ISO and longer exposure would be the go. That was until I saw Octane's wide field view of Scorpius today.

Maybe it's because most of the noise I've is in the red channel and Octane was using an unmodified camera?
Reply With Quote
  #6  
Old 27-02-2006, 03:29 PM
RB's Avatar
RB (Andrew)
Moderator

RB is offline
 
Join Date: Aug 2005
Posts: 21,995
Quote:
Originally Posted by Vermin
I thought using a lower ISO and longer exposure would be the go. That was until I saw Octane's wide field view of Scorpius today.

Maybe it's because most of the noise I've is in the red channel and Octane was using an unmodified camera?
If you go for longer exposures at lower ISO's you get other problems occuring like amp glow, sky glow etc.
Longer exposures also reveal problems with alignment and tracking. If your not using a good quality mount it will show up in longer exposures.
It also depends on what your shooting through and at what f ratio etc.
Octane was using a relatively wide FOV.
If Octane was to shoot the series at say 4-10 min instead of 30 sec exp you'd see more noise.
The whole Idea of shooting more shorter exp is to increase the sig to noise ratio of the final image. At the same time it allows us to use higher ISO's to grab some detail at the same time.
Reply With Quote
  #7  
Old 27-02-2006, 04:17 PM
Striker's Avatar
Striker (Tony)
Whats visual Astronomy

Striker is offline
 
Join Date: Dec 2004
Location: Brisbane
Posts: 5,062
I started out by taking 30 second exposures and thought that was the way to go maybe 50 x 30 second exposure....but since then I have found by doing 20 x 2 minute exposure's provide much more detail then I could ever wish to get on 30 seconds.

Then throw in a dark site and go for 10 x 5 minute exposures.

And obvioulsy with this new requirment I have the same problems Andrew has just mentioned.
Reply With Quote
  #8  
Old 27-02-2006, 06:27 PM
acropolite's Avatar
acropolite (Phil)
Registered User

acropolite is offline
 
Join Date: Feb 2005
Location: Launceston Tasmania
Posts: 8,985
Tom, I think I may have seen a table for exposures in Astronomy 2005, yep a quick check and it's there, page 139 or page 140 in the 2006 version.
Reply With Quote
  #9  
Old 27-02-2006, 08:42 PM
Vermin's Avatar
Vermin (Tom)
Cloud dodger

Vermin is offline
 
Join Date: Dec 2004
Location: Hobart
Posts: 584
Thanks for the heads-up Phil but they are for the moon and planets not DSOs.
Reply With Quote
  #10  
Old 02-03-2006, 01:31 PM
Vermin's Avatar
Vermin (Tom)
Cloud dodger

Vermin is offline
 
Join Date: Dec 2004
Location: Hobart
Posts: 584
Looks like DSLR focus has a suggested exposure time calculator too: http://www.dslrfocus.com/images2/Tools.jpg
Reply With Quote
  #11  
Old 07-03-2006, 11:04 AM
Vermin's Avatar
Vermin (Tom)
Cloud dodger

Vermin is offline
 
Join Date: Dec 2004
Location: Hobart
Posts: 584
Stumbled across some interesting information on sensitivity and dynamic range shown in these graphs that Canon 300D and 20D DSLR owners might like to peruse: http://www.pbase.com/terrylovejoy/dy...itivity_curves
Reply With Quote
  #12  
Old 16-03-2006, 09:56 AM
Vermin's Avatar
Vermin (Tom)
Cloud dodger

Vermin is offline
 
Join Date: Dec 2004
Location: Hobart
Posts: 584
Excellent noise comparison graph of the EOS 20D and 5D Canon cameras at different gains and luminance levels: http://www.ddisoftware.com/20d-5d/ns-prof.jpg

Looks like the 5D has about the same noise level at twice the ISO of the 20D.

Referring page: http://www.ddisoftware.com/20d-5d/
Reply With Quote
  #13  
Old 07-08-2007, 01:13 PM
ozstockman (Mike)
Registered User

ozstockman is offline
 
Join Date: Mar 2007
Location: Kenmore Hills, Brisbane, QLD
Posts: 392
I have found exposure calculation software which seems to be the same as the module built in DSLRFocus.

It can be downloaded from

http://www.covingtoninnovations.com/...astrosoft.html

cheers,

Mike


P.S. I have noticed that it's an old thread :-) I just want to help anyone who will find this thread looking for advices on exposure length.
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 09:23 PM.

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