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 My first attempt - why are the stars not sharp? 
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Joined: Mon Sep 20, 2010 2:54 pm
Posts: 90
Post My first attempt - why are the stars not sharp?
Howdy,
Got my timer yesterday and did a few tests in my back yard. I posted them all here:

http://morningstar.smugmug.com/Other/Time-Lapse-Tests/13936058_XTgrV#1023364363_S5Vde

But in particular I wanted to see if I could get any stars on an almost full moon night. My exposure was:
1DmkIV, iso 1600 (I was afraid that 3200 would have too much noise)
16mm, f/2.8
8 sec exposures, 12 second intervals
sRaw files, processed in Aperture, added some contrast and a little sharpening. exported to 50% jpegs, compression 10
movie file made with Quicktime 7 pro.

I knew the moon would be very much blown out, but was hoping it would move out of frame before I ran out of memory. I was wrong.
Either way, I'm wondering if the stars are what I can expect on a moonless night? They show movement. Is it the lens? The exposure length? Both?
Any advice will be much appreciated.

I was going to embed the video of the stars (with the moon) but I guess I can't do that from SmugMug, so here's the direct link:

http://morningstar.smugmug.com/Other/Time-Lapse-Tests/13936058_XTgrV#1023364363_S5Vde-A-LB


Sun Sep 26, 2010 5:31 pm
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Post Re: My first attempt - why are the stars not sharp?
Hey you've got the dream body there so don't be afraid of 3200 (not that it's necessary under full moon).

Looks like your simply a little out of focus. All lenses are a little different and rarely fall exactly on the infinity symbol. Use live view or take a series of shots around it noting where each one falls. Then you'll know for sure your in the sweet spot.


Sun Sep 26, 2010 7:08 pm
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Joined: Thu Mar 27, 2008 2:15 pm
Posts: 1696
Post Re: My first attempt - why are the stars not sharp?
How did you focus? On a full moon, you can drop your ISO and exposure very low, then literally focus on the moon. It will be super sharp. Use "Exposure Simulation" in Live View mode, then punch into the image 10x.

Why export jpeg at 50%? That seems very low.

Some types of sharpening (like "Clarity" in ACR) can make your stars look like balls, rather than pinpoints.

A couple more things:

Never shoot sRAW for astro. It treats hot pixels as stars, and burns them into your image. For astro, shoot RAW.

Try to have an interval that is shorter than your exposure time for astro. Three to five seconds is the max. If you have 15 or 20-sec exposures, the timelapse can appear choppy.


Sun Sep 26, 2010 7:58 pm
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Joined: Mon Sep 20, 2010 2:54 pm
Posts: 90
Post Re: My first attempt - why are the stars not sharp?
Thank you guys for your feedback! As an aside, I've never participated in a photography forum that was so helpful!

A few notes:
For my focus I put my focus spot on the brightest start, then recomposed. I might have been careless and adjusted the focal length. Also I understand that I should just go ahead and fill up my cards/drives with full size raw files.

I did another experiment last night from Coronado across at San Diego skyline. I wish I had let the camera go longer, and had started earlier but... oh well. I'll post that one for feedback.

Again, thank you both!
-rand


Thu Sep 30, 2010 1:44 pm
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