Just shot this like 15 minutes ago. I have learned 3 things:
- Zoom in on a bright star to focus and then back off
- Lowest aperture possible by your lens (more light the better)
- Highest ISO
In general I am learning, at least for my camera, is that the shortest exposure is key.
So you need to let the most light in the camera possible. It is still extremely hard to get focus. I found the best way is to find a bright star, zoom into it, get a manual focus, zoom out, and take your exposure. Having the lens open all the way lets the most light in and the high ISO sensitivity makes for a rather quick exposure. I realized that as long as you have good focus you could shoot the sky with a 1.2 lens. The stars are so far away that the focal range is basically irrelevant. So stop it wide open!
I shot this in RAW format at 18mm f3.5 1600 ISO for a 6 second exposure, which was a pretty quick exposure for a night time image. You are probably guessing that the image generated quite a bit of noise and you would be correct. Take a look at the original and post processed image below. Via Adobe Lightroom 3 I was able to fine tune this image pretty well. Especially pulling the stars out via the clarity and vibrance slider and reducing the noise with the noise filter.
I would say a definite improvement over my last attempt, and also another example of why you absolutely NEED to shoot in RAW format.
Enjoy the photo!