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Old 27-02-2006, 12:31 PM
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Vermin (Tom)
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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.
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  #2  
Old 27-02-2006, 12:36 PM
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[1ponders] (Paul)
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There are formula around to help Tom, but I mainly use the tables in the back of Michael Covingtons book.
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Old 27-02-2006, 12:39 PM
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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
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Old 27-02-2006, 12:49 PM
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RB (Andrew)
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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.
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Old 27-02-2006, 03:12 PM
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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?
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Old 27-02-2006, 03:29 PM
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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.
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Old 27-02-2006, 04:17 PM
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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.
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Old 27-02-2006, 06:27 PM
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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.
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Old 27-02-2006, 08:42 PM
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Thanks for the heads-up Phil but they are for the moon and planets not DSOs.
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Old 02-03-2006, 01:31 PM
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Looks like DSLR focus has a suggested exposure time calculator too: http://www.dslrfocus.com/images2/Tools.jpg
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Old 07-03-2006, 11:04 AM
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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
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Old 16-03-2006, 09:56 AM
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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/
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  #13  
Old 07-08-2007, 01:13 PM
ozstockman (Mike)
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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.
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