Saturday, May 29, 2010

Photographing the Milky Way

Last year I was fortunate enough to go to Tenerife where, in the volcano's crater, there is not much light pollution so you can see the milky way. Unfortunately I didn't get very good photographs because I didn't have my tripod, having to rest my camera on some clothing on the roof of the car.

Luckily I am going back, and this time I'll have my tripod. But its just a regular tripod, not motorized or anything.

So now I looked into how to take good photos of the milky way, and I've discovered a few things:

  1. If the moon is up, it'll put too much light into the sky. Check site where you can put in different dates and locations to see when the moon rises and sets.

  2. I didn't really know what settings to use, so I tried ISO 2500, f/2,8, 25 seconds, which got me

    From (Very) Amateur AstroPhotography

    ie quite a bit of light pollution, and, blurred stars.

  3. There is always light pollution , which means that if you increase the exposure by increasing the exposure time, you will actually only brighten the sky. Its unlikely you'll get to capture more stars, planets etc

  4. Even relatively dim objects will, at the setting above, cause sensor bloom ie the sensor will go to 255,255,255. This means that you should use the widest aperture you have.

  5. The stars move surprisingly fast. With a 50mm lens on my D300 ie 75mm equivalent, for a 30s exposure I found the stars travelled about 7 or 8 pixels ie the point of light were not points anymore but trails:

    So I set out to find what a better exposure would be, and discovered that
    with an exposure time of 5s the stars moved 1 or 2 pixels:

    An alternative would be to use a wider lens. A 25mm lens would produce half the movement relative to pixels ie 30s exposure would give 3 or 4 pixels of movement, 12.5mm would produce maybe 2 pixels. My problem is that my Tokina 12-24 has a maximum aperture of f/4, and my Tamron 17-50 is f/2.8. So at 17mm on the Tamron 30s would give me ~3 pixels of movement.
So there's my answer. 5s f/1.8 highest ISO without getting too much noise. When I'm there I'll try both.

Final tip. Use a cable release because any slight movement of the camera will cause the stars to become trails.

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