Now for the stars. On a starry, moonless night, put the camera on a sturdy tripod, aim at a familiar constellation, set the aperture wide open, focus on infinity, and take a 10- to 30-second exposure at ISO 400 or 800. You'll get something like Figure 4.5 or Figure 4.6.
For this project, a 50-mm f /1.8 lens is ideal. Second choice is any f /2.8 or faster lens with a focal length between 20 and 50 mm. Your zoom lens may fill the bill. If you are using a "kit" zoom lens that is f /3.5 or f /4, you'll need to
make a slightly longer exposure (30 seconds rather than 10) and the stars will appear as short streaks, rather than points, because the earth is rotating.
If your camera has long-exposure noise reduction, turn it on. Otherwise, there will be a few bright specks in the image that are not stars, from hot pixels. If long-exposure noise reduction is available, you can go as high as ISO 1600 or 3200 and make a 5-second exposure for crisp star images.
Focusing can be problematic. Autofocus doesn't work on the stars, and it can be hard to see a star in the viewfinder well enough to focus on it. Focusing on a
very distant streetlight is a good starting point. Then you can refine the focus by taking repeated 5-second exposures and viewing them magnified on the LCD screen as you make slight changes.
The picture will benefit considerably from sharpening and contrast adjustment in Photoshop or a similar program. You'll be amazed at what you can photograph; ninth- or tenth-magnitude stars, dozens of star clusters, and numerous nebulae and galaxies are within reach.
This is of course the DSLR equivalent of the method described at length in Chapter 2 of Astrophotographyfor the Amateur (1999). It will record bright comets, meteors, and the aurora borealis. In fact, for photographing the aurora, a camera with a wide-angle lens on a fixed tripod is the ideal instrument.
Figure 4.6. Blitzkrieg astrophotography. With only a couple of minutes to capture Comet SWAN (C/2006 M4) in the Keystone of Hercules, the author set up his Digital Rebel on a fixed tripod and exposed 5 seconds at ISO 800 through a 50-mm lens at f /1.8. JPEG image, brightness and contrast adjusted in Photoshop. Stars down to magnitude 9 are visible.
Figure 4.7. Comet Machholz and the Pleiades, 2005 January 6. Canon Digital Rebel (300D) with old Pentax 135-mm f /2.5 lens using lens mount adapter, piggybacked on an equatorially mounted telescope; no guiding corrections. Single 3-minute exposure at ISO 400, processed with Photoshop.
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