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My new Canon SX10 IS has a hot shoe; I've been experimenting with a borrowed Nikon SB-22s flash and have posted my experiments in my Experimental Photos albumn.

Why an external flash?

You may be wondering, "Your camera already has a built-in flash, why bother with a large bulky external flash?" Well, there are a couple of reasons why I like an external flash. First simply has to do with the greater output available from an external flash unit. As you can see in the photos, the external flash can produce far more light than the internal one, and the light covers a greater distance, which is useful when you're shooting in a large area or out of doors.

The second reason is because the flash I'm using can be re-aimed to bounce the flash off a reflector. (reflector in this case can be a flash umbrella, or even the ceiling.) This means that the harsh shadows that appear on the wall behind a subject can be reduced or eliminated.

Setting up a flash

The hot-shoe on my camera has more than just the standard contacts for firing a manual flash. In fact, if I were using a Canon Speedlite flash, the camera would be able to set the flash output to match the camera's exposure settings, resulting in a good picture with no brain-effort.

Unfortunately, the Nikon flash I'm using does not communicate with my Canon camera (no surprise there.) So, I'm left doing things the old-fashioned way, just like back in the film-SLR days. An external flash has a lookup table on the flash body that tells you what aperture to use, giving a certain distance to the subject. These values change based on the ISO of the film you're using; the same holds true for the ISO setting in a digial camera.

Set the camera to manual mode

The camera doesn't know what the flash output power is, so if we let the camera make any decisions on shutter speed or exposure, the resulting photo will probably not turn out.

Adjust the white balance for the flash

The auto-white-balance setting will not be suitable either, so we have to manually set the white balance to the "flash" setting.

Fix the ISO setting on the camera and the flash

In an automatic setting, the camera will auto-adjust the apparent ISO of the image sensor in order to compensate for light levels. We want to fix this value so that the chart on the flash makes sense. I usually use an ISO of 100; don't forget to set the flash to the same value, again so the lookup table is correct.

Set the shutter speed on the camera

Most flashes work on a shutter speed of 1/125 or 1/60. I use 1/125 for my flash photos, and I've had good results so far. The reason for a specific shutter speed is that the flash strobe is not infinitely short; it does have a duration, and the shutter needs to be open long enough to catch all the light. Too slow a shutter speed, though, will result in an over-exposed image, as the lookup table is designed around a certain shutter speed.

Determine the distance to the target

Here you can guess, use a range finder, or use the manual focus setting on the camera to get an idea. (if you put the subject in focus, the camera will tell you what the focal distance is.)

Look up the correct aperture for the distance

Using the lookup table on the flash, determine the correct aperture setting to use for this distance.