External Flash

More options and less red-eye mean better photos

In our learning section on flash, we describe how an external flash attaches to your camera via a hot shoe. If your digital camera doesn’t have a hot shoe (and many don’t) then you can’t use an external flash. Read no further.

For those who do have a hot shoe and wonder about the benefits of an external flash, we’ve got more information for you.

Benefits of an External Flash

There are three primary benefits of using an external flash: the elimination of red-eye, versatility and flash power.

No Red-Eye

We’ve all seen red-eye at some point or another. All of your family members are arranged for that nice portrait and every single one of their eyes is glowing bright red. This is because the flash on your compact camera is very close to the lens.

The good news: with the right software you can quickly and easily eliminate red-eye from all of your digital photographs. The better news: with an external flash, you can prevent red-eye so you don’t have to use any software at all.

For more information and diagrams about the relationship between red-eye and the distance of the flash from the lens, see our section on flash.


A flash on a compact camera only points one direction: forward. It also typically operates at one power: full.

An external flash gives you much more versatility. The flash can be angled up toward the ceiling, or rotated to bounce off a nearby wall. It can be pointed in just about any direction, so you are not always just blasting your subject with light.

Many external flash units also let you tone down the amount of flash produced. In those instances where you just need a small amount of additional light, you can adjust the flash accordingly.


For those individuals who are always looking for more power, an external flash is the way to go.

The power of the flash determines the amount of space it can light up. Let’s start with a dose of reality — no flash, no matter how powerful, is going to light up the Sistine Chapel.

However, if you are in a large room and taking a group photo, the small flash on your compact camera may not emit enough light to get a properly exposed photograph. In this case, you need something that is going to cover more distance, which means you need a more powerful flash.

Features of External Flash

There are several factors to consider when you purchase an external flash: guide number, type of flash head and recycle rate.

Guide Number

A guide number (GN) is used to indicate how much light a flash will produce when it goes off. As the guide number gets higher, the intensity of the light increases as well as the distance the light can travel.

Guide numbers are measured in feet (or meters), but don’t take this literally as “how far away can I be and still light something up.” Many factors will affect the physical distance the flash can cover: from outdoors to indoors, the amount your flash can light up will vary. Most guide numbers assume that your digital camera is set to ISO 100.

Here are some examples of Canon Flash units and their respective guide numbers:

FlashMax Guide Number
220 EX    7222
420 EX13842
550 EX18055
580 EX19058

The guide numbers increase along with the model numbers, and so does the price. While the 220 EX costs about $115 the 580 EX costs about $480.

Flash Head

There are two types of flash heads: fixed and full swivel bounce. A fixed flash points straight ahead, the direction the camera is pointed. The only difference between the fixed flash and your camera’s built-in flash is that one is further away from the lens so you should get less red-eye in your photos.

A flash with a swivel bounce head is not stuck pointing straight forward. The swivel allows the flash bulb to twist to the left and right, and the bouce allows the flash bulb to be tilted up toward the ceiling rather than straight ahead. The idea behind the “bounce” is that rather than shooting light straight at your subject, you bounce the light off a reflective surface (white wall or ceiling) instead.

Swivel and bounce gives you much more creative freedom when you’re working with flash. You can bounce the flash of any available surface to create soft lighting effects. The swivel lets you direct light to the right or left, rather than straight on ahead.

Recycle Rate

If you really are going to use your external flash a lot, then recycle rate is going to be VERY important to you. Here’s why.

Imagine that you are photographing a fast-moving subject, say your best friend’s miniature pet poodle. If you are outside in natural light (where you don’t have to use flash) then you can set your camera to continuous shooting mode, and take photos in burst of 3 and 4. This will ensure that you have some nice photos, even though your subject is moving all over.

When you are stuck indoors with a flash that is slow to recycle, you can’t do this. You take one photo, the flash goes off, then you have to wait. Once the flash recycles (and is back to full power again) then you can take another shot.

If you don’t wait for your flash to recycle, the next photo you take is bound to be under-exposed. Since the flash is not at full power, it can’t emit enough light to get a proper exposure.

A flash with a fast recycle time reduces the amount of waiting you have to do between shots when you can’t rely on any natural light to help you out.

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