September 2008
Beginner to intermediate
288 pages
9h 36m
English
Content preview from The Canon EOS Digital Rebel XSi/450D Companion
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CHAPTER 10
USING AN EXTERNAL FLASH
234
Using an External Flash
On the top of the camera sits a hotshoe, a fairly standard camera interface that
allows you to use a number of different accessories. It’s called a hotshoe because
it’s an interface that provides electrical contacts through which the camera can
communicate with an attached accessory (as opposed to a coldshoe, which has
the same type of mount but provides no communication between the camera
body and whatever’s in the shoe).
You can attach an external flash to the hot shoe on the top of the camera.
You can use the hotshoe to attach special wireless or wired remotes, levels (for
ensuring your camera isn’t tilted), umbrellas to keep your camera dry, and other
specialized accessories. But hotshoes are most commonly used for external flash
units.
Even though the XSi has a built-in flash, there are a number of reasons to use an
external flash. ey’re more powerful, so they can cover a longer range and of-
fer more latitude for exposure adjustment. Flash units all provide a specification
called a guide number that indicates how powerful the flash unit is. For example,
on page 180 of the Rebel XSi’s instruction manual, you’ll find a listing for Guide
Number: 13/43 (ISO 100, in meters/feet). is number represents a constant that
you can use to determine the range of the flash at a given aperture. For example, a
guide number of 43 indicates th ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.