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PostPosted: Fri Oct 03, 2008 2:19 am 
I'm lucky enough to live far away from any towns and associated lighting, so in any given reasonably clear summer night, portions of the Milky Way can be seen stretching across the sky. I have several images I've taken of different parts of the sky, but I have yet to do any post-processing on them.

In order to avoid waiting 30 seconds to a minute in between shots, I turned off the in-camera noise reduction on my 40D. So now I have a bunch of images and a bunch of corresponding dark frames.

I have two questions:

1.) Is it beneficial to do dark frame subtraction while the images are still in RAW format? It would make the most sense to me to remove the noise first, and then do the other post-processing afterward, as any post-processing might alter the noise in the images and result in a less accurate subtraction if the subtraction were done last. Are there any programs out there that will allow you to do this (that is, edit in RAW)? The only program I have right now that can read the Canon RAW files is the Canon DPP software -- if I want to work with them (like doing a dark frame subtraction), I have to turn them into JPEGs and send them to Photoshop 7.0. Are there any alternatives out there?

2.) I read today that dark frames need to be taken very soon after the actual images are taken, since the hot pixels on a sensor change over time. The images I've captured are from several different days over the past 3 months, and I only just made my dark frames today! Is this likely to cause problems for me?

...And of course, any other advice/tips would be appreciated as well. It took a lot of standing out in the chilly night to capture these images -- I want to make them look their best!

Here's a quick sample of one of my images I captured from my front yard late August, facing SSW -- JPG straight from the camera, with no PP. You can see these will need some work!


Canon 40D
EF-S 17-55mm f/2.8 IS USM @17mm
Aperture: f/2.8
Shutter: 45 sec
Speed: ISO 1600

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PostPosted: Fri Oct 03, 2008 7:47 am 
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Joined: Tue Feb 05, 2008 9:14 am
Posts: 599
Location: Netherlands
I can't really give any advice, but what an awesome shot! I'd love to live further away from the city someday, out here you'd be lucky to spot a few stars...

Canon 5D + 17-40 F4L + 50 F1.4 + 70-200 F2.8L
Velbon Sherpa 200R

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