This week's photographic super power is shooting stars. The first decision you'll want to make is whether or not you want star trails or fixed stars. The easiest way to take star trails is to put the camera on a tripod, then expose for as long as the battery in the camera will let you. Some people use a lot of individual pictures, of about 20 second or 50 second pictures and then stack them. There are advantages to it. You could make a video with it, decrease digital noise, and remove things that are in the way. There's freeware called StarStax for the Mac, Windows, and Linux. This will give you a lot of options on how to stack the photos together, or fill gaps between the individual pictures. Chris does a wide-angle for this.
The other kind of picture is the fixed stars. Star trails happen quicker than you think, so avoiding them will be a challenge. Chris goes with the 600 rule. It depends on the focal length -- when you shoot with a wide-angle you can move the camera a bit more, but when there's a long telephoto lens, a little motion of the camera will show. So the longer the focal length, the shorter the time that you shoot. The 600 rule means to take 600 divided by the focal length. That's the number of seconds you can shoot without getting too much motion in the stars. For example, if you're shooting with a 50mm lens, 600/50 = 12 seconds.
Of course, to get enough light from the stars with shutter speeds anywhere between 10 and 50 seconds, you will need a higher ISO. Or, another trick is to use a tracker that they actually put between the camera and the tripod. It's a mechanical device that turns the camera and evens out the motion of the earth. This allows you to expose for several minutes without having the stars move. Even the entry level trackers will set you back a few hundred dollars.
Next week we review our assignment, "Fly." Join the Tech Guy group on Flickr, post your photos to the group, and we'll share three of Chris' favorites.