Now it's time to take the picture. Obviously, you can't just press the button with your finger; the telescope would shake terribly. Nor do DSLRs take conventional mechanical cable releases. So what do you do?
There are several options. If the exposure is 30 seconds or less, you can use the self-timer (delayed shutter release). Press the button; the camera counts down 10 seconds while the telescope stops shaking; and then the shutter opens and the picture is taken.
That won't work if you're using "Bulb" (the setting for time exposures). You need a cable release of some kind.
Nikon makes an electrical cable release for the D70s and D80, but for most Nikon DSLRs, your best bet is the infrared remote control. Set the camera to use the remote control, and "Bulb" changes to "- -" on the display. That means, "Press the button (on the remote control) once to open the shutter and once again to close it."
With the Canon Digital Rebel family (300D, 350D, 400D), you can buy or make a simple electrical cable release (see p. 119). This is just a cable with a 2.5-mm phone plug on one end and a switch on the other.
Some people have reported success by simply plugging a cheap mobile telephone headset into the Digital Rebel and using the microphone switch to control the shutter. This is not as silly as it sounds. The headset can't harm the camera because it contains no source of power. It may have the right resistance to work as a Canon cable release. If not, you can take it apart and build a better cable release using the cable and plug.
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