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Old Feb 2, 2012, 8:29 PM   #11
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Originally Posted by BillDrew View Post
You got the moon in proper scale. The moon is 0.5182 deg across when viewed from earth. The stars track at .25 degrees per minute, or 0.0625 degrees in 15 seconds, a ratio of eight (0.5185/.0625). The moon in the photo is seven or eight times wider than the length of the trails.
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Old Feb 3, 2012, 5:42 AM   #12
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BillDrew- Renaissance man, or scientist?
I was asking myself the same thing!
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Old Feb 3, 2012, 6:11 AM   #13
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Quote:
Originally Posted by BillDrew View Post
You got the moon in proper scale. The moon is 0.5182 deg across when viewed from earth. The stars track at .25 degrees per minute, or 0.0625 degrees in 15 seconds, a ratio of eight (0.5185/.0625). The moon in the photo is seven or eight times wider than the length of the trails.
NO S[tuff]!

The star trails were taken at a focal length of 85mm at f/8 for 60 seconds (not 30, like I mistakenly said in my earlier post), while the Moon was taken at a focal length of 300mm at f/8 for 1/250 second.

JOOC, The shot only contains star trails and the Moon. Who's to say which is to scale?
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Old Feb 3, 2012, 9:11 AM   #14
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I am thinking you are after something like this?
http://500px.com/photo/4776819?from=popular
90 minutes of stacked 30 second exposures.

that image is not mine, though I wish it was!
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Old Feb 3, 2012, 9:32 AM   #15
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It needs a Moon.
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Old Feb 3, 2012, 11:34 AM   #16
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I am thinking you are after something like this?
http://500px.com/photo/4776819?from=popular
90 minutes of stacked 30 second exposures.

that image is not mine, though I wish it was!
Yes although I was hoping to do it in one long exposure which looks like a lost cause. I've done a bit of experimenting and If I set the camera to say 10s exposures on the burst shutter mode and lock the cable release then it will just keep shooting until I stop it. If it's clear tonight I'm all set to try again - can start it and then retire inside for a hot chocolate for half an hour or so.
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Old Feb 3, 2012, 12:09 PM   #17
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You may also want to use the 2 second self-timer to avoid the mirror slap shaking your tripod.

Your A580 is capable of 30 second exposures, which will work just as well as 10 second exposures, and you only have to handle a third as many files. Also, a 30 second exposure time will greatly reduce the gaps resulting from the 2 second self-timer.
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Old Feb 3, 2012, 12:16 PM   #18
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Thanks TCav. I saw some tests with a dslr with a laser pointer attached which suggested the mirror slap was a pretty small effect and on a long exposure any shake from the slap should be lost I think. I'll try a bit of a scientific test though and use a few different methods for 15 minutes at a time and see what the differences are.
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Old Feb 3, 2012, 12:45 PM   #19
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This is a single 1 hour exposure at iso 800 by an acquaintance of mine
Canon EOS 1ds-MKiii ISO800, most cameras don't manage very long exposures like this without building up huge amounts of noise due to heat.

http://500px.com/photo/4179903
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Old Feb 3, 2012, 1:50 PM   #20
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OK, I think I've got it. Unfortunately within 5 miniutes of me starting, a beautiful still clear night had clouded over and half way through a low flying plane went through the middle. So, considering the trails are short because of the clouds and there's a gap where I discarded the plane frames, I think it's showing some promise.

f3.5, 15s, ISO-800, 16mm, a580+16-80CZ

I think there's a bit of distortion at 16mm but not too bad.

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