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Old 22-07-2012, 10:00 AM
TheDecepticon
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Wide Field

Howdy,

What is the generally accepted way to focus a camera and lens assembly for wide field sky shots.

I tried again last night while we were out, and had auto focused on a distant object, but then all the stars clearly show out of focus. I was using my 40d with an EFS 17-85 lens.

Thanks in advance,

Gray.
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Old 22-07-2012, 10:15 AM
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multiweb (Marc)
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Quote:
Originally Posted by TheDecepticon View Post
Howdy,

What is the generally accepted way to focus a camera and lens assembly for wide field sky shots.

I tried again last night while we were out, and had auto focused on a distant object, but then all the stars clearly show out of focus. I was using my 40d with an EFS 17-85 lens.

Thanks in advance,

Gray.
I use the star profile in nebulosity and confirm with a bathinov mask with my QHYs. With the SONY I use live view zooming right in (7x).
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Old 22-07-2012, 10:27 AM
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Octane (Humayun)
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40D has Live View!

Otherwise, use the infinity mark on the lens focus ring.

H
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Old 22-07-2012, 10:58 AM
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CapturingTheNight (Greg)
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In the absence of a computer hookup to use software, I use magnified live view to zoom in on the brightest star/planet I can find and manually focus the lens on it until it is as tight as possible, and then switch the lens to AF. I have the camera setup for back button autofocus only meaning that the lens wont try and change focus when I press the shutter button and wont slip focus during the night.

Not sure if the 40d has live view though? (Edit: Well H just said it does)

The other thing you can do is work out the hyperfocal distance of your lens/ camera/aperture combo. There are numerous online calculators for this. The hyperfocal distance given means that if you, say place a flash light or get a friend to hold a flashlight at that distance from the camera and you focus on it- Everything from that distance to infinity (ie. the stars) will be in focus. Add a meter or so to the given distance. Best to sacrifice a meter of focus in the foreground than miss getting infinity.

Hope this helps.
Cheers
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Old 22-07-2012, 12:34 PM
TheDecepticon
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Thanks guys,

I didn't have a lap top as the new battery I had ordered had not arrived so I was doing it manual. I did actually forget that I could use live view and zoom in. I don't get much time to try this type of photography and by the time I get to try again, I've forgotten it as I don't write anything down.

Better luck next time. I'll look up how to use one of those calculators, too.

Cheers!
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Old 22-07-2012, 02:37 PM
Auster1b (Neil)
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40d live view

Gray,
On my 40d I use Live View and Manual Focus on a bright star and 10x mag to zoom in.

You may have to also set Live View exposure simulation for long exposures to pick up stars etc.
Custom function: C.Fn IV-7 (pg 163 in my manual)

Neil.
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