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This photo was more of a technical exercise rather than an attempt to create art, but I was so pleased with the eventual outcome that I decided to enhance the image and post it anyway.
I love looking at stars, planets, comets, the Milky Way and other celestial entities. After all, the heavens declare the glory of God don't they?
But as well as looking at the night sky I also want to be able to photograph what I see to the best of my and my equipment's ability, hence an experiment I conducted one cold winter's night up in the mountains near where I live in North Wales.
I wanted to find out what lenses, what apertures, what ISO's and what exposure times worked best, so I took shots of the night sky with my Canon 17-40mm zoom, 24-105mm zoom and 50mm f1.4 prime lenses, mounted on my Canon 5D set to ISO levels up to 800.
What I found was very helpful, and a few guidelines are noted below.
My 17-40mm lens at maximum aperture of f4 is a bit soft. On the other hand my 24-105mm lens is much sharper at f4, but doesn't give such a large field of view.
My 50mm prime gives a sort of halo effect (not unpleasant) at f1.4 maximum aperture. Closed down to f1.8 it is the sharpest of the bunch, but at 50mm focal length I can only fit one constellation in at a time.
My good old Canon 5D was the best of its class for noise when it came out in 1995. Now my consumer Nikon D3100 beats it hands down.
I found I need to use ISO of up to 200 only if I want to keep noise to a manageable (correctable) level wqith the 5D.
Not so good if you're using f4 maxium aperture lenses.
Obviously, if you're using a low ISO and you've stopped your lens down a bit to increase sharpness you'll need as long a shutter speed as possible to get enough light to make an exposure at night.
This is where the 'rule of 600' applies, in that if you want to avoid the stars streaking because of the earth's rotation, your shutter speed needs to be at most 600/focal length in seconds.
So for my 50mm prime lens, which I used to take this shot, the maximum shutter speed I could use before obvious streaking occurs is 12 seconds (600/50=12).
Of course, if you want to record the stars as streaked arcs that's a whole different scenario, and may be the subject of further discourse based on another image in the future.
With the gear I have available at the moment I'm struggling with the compromises between field of view, noise and sharpness when it comes to photographing the night skies.
To achieve better results I need to get a wide angle lens of maximum aperture f2.8 or less that's sharp wide open and a camera body that gives less digital noise at high ISOs. Let's see how generous Santa's feeling this year!
By the way, the stars shown in the Orion constellation here have been enhanced significantly in PhotoShop, otherwise you wouldn't be able to see them at screen resolutions!
There are a few 'unenhanced' stars in the frame also, which you can just about make out.
Filename - stars orion 02.jpg
Camera - Canon 5D
Lens - 50mm prime
Exposure - 10secs @ f1.8, ISO100
Location - The night sky, North Wales
This image - 800x640px JPEG
Conversion - ACR & PS-CS2
Comments - Tripod, mirror lockup and cable release used to prevent camera shake
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