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Old 24-11-2008, 10:06 AM
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Benno85 (Ben)
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Exposure Times for Widefield

Hi All,

Is there a general guide as to the maximum exposure time for widefield astrophotography before star trails become visible?? At the moment all my setup consists of is a 450D and a tripod with shutter cable (plus the standard 18-55mm kit lens that came with the camera body)

As you can tell, I'm very new to all of this!!!!
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Old 24-11-2008, 10:52 AM
DJDD
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Hi,

This is info given me by someone else on the forum, and is a rough guide.

Maximum exposure time before trailing is evident isL

t = 1000/FL (near the pole)
and
t = 700/FL

where
t = exposure time
FL = focal length of lens

of course, this is a rough guide.

also, see this thread for what is possible:
http://www.iceinspace.com.au/forum/s...ad.php?t=21306
with 50 x 10 second exposures

and my poor first attempt with 10 x 13 seconds for comparison:
http://www.iceinspace.com.au/forum/s...ad.php?t=23805
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Old 24-11-2008, 01:59 PM
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At a guess I'd say around 15 seconds.

Greg.
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Old 24-11-2008, 08:13 PM
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Thanks to you both for the input. Based on these replies, is it safe to generally assume that 50 x 15sec still (i.e. tripod mounted) images can yield decent results with the right amount of post-processing?
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Old 24-11-2008, 08:23 PM
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Based on Luka's efforts:
http://www.iceinspace.com.au/forum/s...ad.php?t=21306

I would say so.

cheers.
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Old 24-11-2008, 09:03 PM
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Can't remember where I found the formulae for the attached table , will post it if remember but this will probably help


ie a 200mm f/2.8 will give 11th mag stars in 2.1 seconds with a star trail 0.51min arc long. Worked OK when I was photographing the comet in Jan last year with just a camera on a tripod.
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Old 27-11-2008, 10:52 PM
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It depends on the focal length of your lens and also which area of the sky you are imaging. Closer to equator means that longer exposure time is possible.

The simple way is to forget about formulas and just take a 10s exposure, zoom in and see if you see trailing. If there is no trailing try longer exposure. If there is trailing reduce exposure. In several shots you will have the answer.
Digital makes the life easy.

Scroll down in the thread mentioned above for some hints.
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Old 28-11-2008, 08:25 AM
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Quote:
Originally Posted by Benno85 View Post
Thanks to you both for the input. Based on these replies, is it safe to generally assume that 50 x 15sec still (i.e. tripod mounted) images can yield decent results with the right amount of post-processing?
Just to show you a concrete example: I was in the States a few years back without a scope when I took this picture of the big dipper.
Canon 350D, 27mm focal length, 6 exposures of 20 sec at iso 400.
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