Digital Photography Hacks [Electronic resources] نسخه متنی

Hack 45 Freeze Action with Electronic Flash

The hand is quicker than the eye, and your
electronic flash is faster than your shutter. Use it to stop time and
capture that magic moment.

The shutter on your camera can reach speeds
of 1/2000 of a second or faster. The faster the shutter speed, the
easier it is to stop actionthat is,
freeze your subject in its tracks or, in the case of Figure 4-13, in mid flight. The challenge with a fast
shutter speed is that it also severely reduces the amount of light
passing to the image sensor. So, you have to either open up the
aperture all the way (f-2.8 or so), increase your ISO speed (to ISO
400 or more), or both. And even then, you still might not have enough
light to capture the picture.

Figure 4-13. A hummingbird captured in flight with flash

But there's a workaround for these limits imposed by
the laws of physics. Your camera's electronic flash
is an excellent tool to stop action when you don't
have enough light to use a super-fast shutter speed.

In fact, even when you do have enough light, you still might want to
use the flash. Why? Your camera's shutter probably
tops out at 1/2000 of a second or so. But the electronic flash is
just getting warmed up at that speed, and some external units can
emit bursts of light as short in duration as 1/50,000 of a second.
Now that's high-octane performance!

And it gets even better. Since the flash adds light to the scene, you
don't have to fiddle as much with aperture and ISO
settings. It's rare when you get to have it all in
photography, but this is one of the few occasions where
that's possible.

To use this technique, you first have to make sure the flash fires.
If you're outdoors, switch to
Fill Flash
or Flash On
mode. Now, make sure you're within range of your
flash. For most built-in units, this means eight feet or closer. You
can extend this range if your camera accepts an external flash, which
is more powerful.

If you're using a point-and-shoot digicam,
you're still going to have to deal with
shutter lag: the delay from the moment you press the
shutter to when it actually fires. You'll have to
anticipate the decisive moment and shoot accordingly. Digital SLR
shooters have more responsive cameras and don't have
to compensate nearly as much for lag. Get to know your camera, and go
from there.