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  Canada Nature Star Photography
(Entered Sep. 07, 2010)
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No doubt you've had it happen to you at least once. You're out in the countryside in the middle of the night, you look up into a perfectly clear sky and see millions of stars. Amazed, you try to take a photograph of this wonder. You point your little digital camera up into the sky and click, but all you get on your LCD is pure blackness.
Shooting the night sky is surprisingly difficult. To do so there are a few things that are a necessity. You'll need a tripod at the very least, as well as a camera that allows you to: take long exposures, change the aperture, and adjust the ISO (sensor sensitivity). Of course it also helps to be in an area that is not drowned by artificial light, such as in a city or even a whole country (if you've ever seen a satellite image of Japan at night you'll know what I mean). Other factors are things like clouds and haze. Clouds will of course obscure any stars, but even atmospheric haze (from hot muggy weather or pollution) on a clear night can obscure stars and make them seem dim and fuzzy.
However even if you've got the above equipment covered, and the air is clear and crisp, you'll soon realize that there's another problem which is a bit more difficult to deal with: the Earth's rotation.
When you photograph stars, you generally have to use a long exposure. However if your exposure time is more than about 30 seconds, you'll notice that the stars begin to look more and more like lines instead of dots. I found that an exposure time of about 25-30 seconds is the maximum that you can use before the stars start to show some obvious motion blur. To compensate for a shorter exposure time, you need to increase your camera's ISO, and widen the aperture. I took the below shot with a shutter speed of 25 seconds, an ISO of 800 (higher than that and some graininess started creeping in) and an aperture of f/2.8

stars big dipper

In the photo below you can clearly see the effect of the Earth's rotation, which can be kind of cool if that's the look you're going for. This photo was taken with a shutter speed of 350 seconds, an ISO of 400 and an aperture of f/8 (to keep the image from being too overexposed). Incidently this is also a good way to find Polaris (the North star). Seeing how Polaris is situated almost directly above the north axis point of the Earth's spin, to an Earthbound observer, it seems to stay in the same position relative to the stars around it (which is of course the reason seafarers used it centuries ago to navigate). Polaris is the pinkish tinted star just above center, about a centimeter away from the left border. Oh and if you're wondering why some stars leave blue streaks and some leave orange or yellow, it has to due with factors such as their age, composition and temperature. The youngest, hottest stars are bluish, while the reddish ones mean the star is cooler and/or older.

stars earth rotation

Another interesting point of star photography is that a quality camera can 'see' many more stars than the unaided human eye. With a shutter speed of 64 seconds, an ISO of 800 and an aperture of f/2.8, more and more (previously imperceptible) stars begin to appear.

star photography

With a shutter speed of 155 seconds, a thick, bright band (the plane of our galaxy), starts to appear (below image), albeit with some unappealing motion blur and graininess.

milky way

I suppose the next piece of equipment I need (to get tack sharp photographs of the night sky) is some kind of specialized mount that slowly pans across the sky, compensating exactly for the Earth's rotation, but I'm sure something like that would cost crazy amounts of money. If anyone has a better, cheaper solution, I'd love to hear it!



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