Slow Shutter Speeds and Long Exposure Photography
Many new cameras will come with built-in shutter speeds of up
to 30 seconds or longer, which is enough for most long-exposure
photography. Other cameras will have a B (bulb) setting that
will keep the shutter open as long as you keep your finger on
the shutter release button or a T (time) exposure setting that
will keep the shutter open until you press the shutter release
button a second time. Cameras with bulb settings can also be
fitted with a locking cable release so that it isn't necessary
to keep your finger on the shutter for long exposures. If your
camera doesn't have a cable release, you can use the self-timer
option found on most cameras. This will eliminate camera
vibration from your hands.
A tripod, or something to rest your camera on, is essential
because the camera must be completely still during the time that
the shutter is open. If you want to make a fast-moving car blur
as it speeds by you, a relatively fast shutter speed of 1/20 of
a second may give you the results you are after, however, if you
want to make stars in the nighttime sky look like glowing rings
as the earth rotates, your exposure may last all night.
The light meter on your camera may not be able to accurately
judge the best aperture setting for longer shutter speeds,
especially in low-light situations, so your best bet is probably
to "bracket." This means taking up to six pictures of the same
subject, but doubling the shutter speed each time. This will
give you a variety of effects and exposures and allow you to
choose the best shot. In general, slow shutter speeds will allow
a lot of light into the camera, which means that you will want
to use a small aperture (ie. f/22) to avoid over-exposing the
shot. In bright daylight it will be necessary to use the lowest
ISO available and a neutral density filter to cut the light down.
Some great effects and shutter speeds to try are:
Moving stars: several hours Moving cars at night: 10 seconds
Waterfalls: 4 seconds + Amusement park rides: 1 second