Aurora Borealis Over Ottawa (pic)

Started Mar 10, 2004 | Discussions thread
Luminus
Regular MemberPosts: 155
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Re: Aurora Borealis Over Ottawa (pic)
In reply to Luminus, Mar 11, 2004

You can, but a simple subtraction will leave black spots (so instead of hot pixels you get...well cold pixels :P). If hot pixels show up in black background, this will be okay. Most of the times they will be where you don't want to see black dots (like right in the middle of the lovely Aurora). These dedicated programs have the option for simple subtraction as well as more sophisticated stochastic methods to guess the original color of the subtracted hotpixel from the surrounding pixels.

Of course, you can do this manually in PS using clone tool....but you will be spending a lot of time doing it.

Luminus wrote:
A1's dark frame subtraction won't get rid of hotpixels. You have
to do it again yourself. See my earlier post.

howard1 wrote:
This was ISO800 25 seconds. It turned out to be "overexposed" a
bit. I took some later at ISO400 10 s, but unfortunately, by then
the aurora was less spectacular, and the camera had heated up and
there were many hot pixels. The darker ISO400 shots were still
noisy, however.

I doubt the A2 is any better.

Note that the A1 already does dark frame subtraction for exposures
over 1 s. It's an option you can turn on in one of the menus.

howard1 wrote:

Shot tonight. Auroral activity was very strong for a couple hours.
That orange glow to the left is not the rising sun, it's blown out
glow from sodium street lights in a neighbourhood across the river.
I got down to the river for just the last 5 minutes or so of
activity. This was from my first shot when the camera was cold
started at -7 Celsius. Are those stars or hot pixels in the sky?
I'm not sure. As time went on, I saw more and more hot pixels in
the results, because many of them began to appear even in the snow
in the foreground.

I'm not really happy with the A1's performance for time exposures.
Noisy despite in-camera noise reduction and Noise Ninja post
processing.

http://www.pbase.com/hsandler

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