Contributed by: evilscientist
Just before I left for my vacation I picked up a new camera. I've always wanted a Nikon digital SLR, and they've come down enough in price that I can afford one. So I picked up a Nikon D50 with a couple of lenses. It's a nice camera, 6.5 megapixels, has a nice heft to it and it will accept all the Nikon film lenses I've accumulated over the years.
So I've been going picture happy, which is what anybody does with a new camera. What I've also done is tried out the camera at astro-photography, that is taking photographs of the night sky. The digital camera makes this a lot easier for a couple of reasons.
First, instant gratification. I get to see if the picture turned out while still at the telescope. If it did, then I can move on, if not, I get to try again. With a film camera I'd have to wait till the film was processed then go out on another night to try again.
Second, reciprocity failure. The digital camera doesn't suffer from this. Film suffers from what is known as reciprocity failure. This is the tendency of a film to slow down as exposure time increases. For example, a 1600 ASA film may, after 30 seconds of exposure act like a 60 ASA film as most of the large silver particles have become activated by the photons of light striking them. This isn't a problem with terrestrial photography since there's usually lots of light and the shutter speeds measured in fractions of a second. It is a huge problem for astro-photography with exposure times measured in minutes or hours. The CCD that is the image sensor on the camera doesn't suffer from reciprocity failure, so if it's told to act like 1600 ASA film, it acts that way for the whole exposure, not just the first few seconds. This shortens exposure times to get the same image.
So here's one of my first attempts, it is M57, the Ring Nebula in the constellation of Lyra. It is a two minute exposure taken with my D50 attached at the prime focus of the Wilson Coulee Observatory's 14 inch Celestron telescope. The ASA equivalent of the sensor was set to 1600. The photograph was taken at 00:51 MDT on 10 July 2005.
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Evilness
http://www.evilscientist.ca/article.php?story=20050711194733518