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Old 23rd of July 2012 (Mon)   #1
VaiFanatic
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Default Focusing the image

I've seen some amazingly clear/sharp images of the night sky, but I never seem to be able to focus right. Everything is slightly blurry.

I've been using my nifty-fifty with an f-stop of 1.8, mostly at around ISO 800, f/2.8, with 8 second exposures.

What's the best thing for me to do to focus the lens so it's crystal clear?
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Old 23rd of July 2012 (Mon)   #2
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Default Re: Focusing the image

f/11
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Old 23rd of July 2012 (Mon)   #3
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Default Re: Focusing the image

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Originally Posted by B Koo View Post
f/11
Only if you really enjoy star trails. And even then, not really.

Live View, zoomed to the max if you have it. Otherwise, a bunch of test shots at various focus distance. You could maybe try auto-focusing on the moon if it's out, though I can't guarantee the results.
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Old 23rd of July 2012 (Mon)   #4
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Default Re: Focusing the image

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Originally Posted by armis View Post
Only if you really enjoy star trails. And even then, not really.

Live View, zoomed to the max if you have it. Otherwise, a bunch of test shots at various focus distance. You could maybe try auto-focusing on the moon if it's out, though I can't guarantee the results.
I've tried the auto focus approach with the moon before, images turn out OK, more or less. I've been using Live View zoomed to the max, and manually focusing, but I'm never quite sure of how well I'm focused.

I'll try again tonight.
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Old 23rd of July 2012 (Mon)   #5
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Default Re: Focusing the image

Here are two jpgs stacked together. Couldn't use the raw files because I wasn't using the latest beta.

My processing skills aren't all that great at all either.

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Old 23rd of July 2012 (Mon)   #6
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Default Re: Focusing the image

Quote:
Originally Posted by armis View Post
Only if you really enjoy star trails. And even then, not really.

Live View, zoomed to the max if you have it. Otherwise, a bunch of test shots at various focus distance. You could maybe try auto-focusing on the moon if it's out, though I can't guarantee the results.
^^^^This.

If the moon is out the sky will not have the contrast you want. A bright star should do to focus on. Like the post above said, use live view zoomed in to the max. Use MANUAL focus, focus to infinity then back it off ever so slightly to find the sweet spot. Most lenses focus just past infinity so you have to fiddle with it slightly to get it right. Keep your aperture all the way open - you need all the light into the lens you can get.

Yes, your processing skills need work - that will come slowly as you practice more, but processing won't help you if you don't get the focus right and capture some decent photons!

I hope this helps.
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Old 23rd of July 2012 (Mon)   #7
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Default Re: Focusing the image

Quote:
Originally Posted by A.S.I.G.N. Observatory View Post
^^^^This.

If the moon is out the sky will not have the contrast you want. A bright star should do to focus on. Like the post above said, use live view zoomed in to the max. Use MANUAL focus, focus to infinity then back it off ever so slightly to find the sweet spot. Most lenses focus just past infinity so you have to fiddle with it slightly to get it right. Keep your aperture all the way open - you need all the light into the lens you can get.

Yes, your processing skills need work - that will come slowly as you practice more, but processing won't help you if you don't get the focus right and capture some decent photons!

I hope this helps.
Thanks! I'll give it another shot tonight. The moon will be setting early for the next few days, so I don't have to worry about it. I've been practicing focusing on stars, but I can't ever tell if I've hit that sweet spot or not. It's times like these I wish some folks with similar interests lived near me that I could get together with.
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Old 24th of July 2012 (Tue)   #8
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Default Re: Focusing the image

Usually the sharpest is when the bright star seems the smallest. Out of focus star at maximum magnification looks like a doughnut!
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Old 24th of July 2012 (Tue)   #9
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Default Re: Focusing the image

Didn't get a chance to really try last night. I got incredibly tired, so I knocked out before midnight. Hopefully tonight I'll be awake long enough to try for some better results!
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Old 29th of July 2012 (Sun)   #10
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Default Re: Focusing the image

Another attempt has yielded no better results. I've used live view to focus, and I've used AF on a distant light, and nothing seems to be getting it just right. Stars around the center are somewhat clear, but off in the corner the really blur and even seem to have an oval halo around them.

I shot this at f/1.8, ISO 400 for 5 seconds. I took 1 others and stacked them, but the halos were only exaggerated further.


IMG_2163 by VaiFanatic, on Flickr
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Old 29th of July 2012 (Sun)   #11
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Default Re: Focusing the image

The corners of a star shot with my 50mm f1.8 are terrible. Supposedly it gets better if you stop it down, but then you end up needing a lot longer exposure than you would at 1.8.
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Old 30th of July 2012 (Mon)   #12
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Default Re: Focusing the image

Hmm, I've been distracted by web development, so I haven't had a chance to go out tonight, but we shall see. I've taken a picture before with the 50 wide open and the corner stars were not that bad.
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Old 4th of August 2012 (Sat)   #13
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Default Re: Focusing the image

If there is enough light, stopping you lens down just a bit will improve overall sharpness and make it a tad easier to focus as well.
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Old 5th of August 2012 (Sun)   #14
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Default Re: Focusing the image

I'll give it a try tomorrow night.
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Old 6th of August 2012 (Mon)   #15
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Default Re: Focusing the image

I've figured it out, why all of my images on the tripod have been coming out so terribly. Well, it's an old tripod from the 70s, for a Minolta. It's more or less a portable option until my nice manfrotto gets here.

When the shutter goes off, it moves the causes the camera to jerk ever so slightly, causing motion blur.

I did my best to ground the tripod, and got a much better result, but couldn't repeat my efforts.

But now I now I know what my problem is.
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