3 Top Ten FAQs

1

My camera already has a built-in flash. Why should I buy an external one?

That depends on what you want to do with your photography. Popup flash units are great for simple snapshots. You can’t lose them unless you lose the whole camera, they don’t add weight or bulk, and no extra batteries are needed.

On the other hand, the light from a popup flash is limited in range and tends to create harsh-looking photos. External flash units always provide much more power, and thus greater lighting distances. External flashes are also more flexible lighting devices, and they can enable the creation of more attractively lit photos when using the proper techniques. For example, an external flash with a swiveling head can be used to bounce light off a nearby wall or ceiling, resulting in softer lighting than direct flash.

Admittedly, flash can’t solve every photographic lighting problem. It’s a valuable tool, but sometimes the best way to ruin a nice picture is to blast tons of light onto the scene with a flash unit. Available light photography forces you to slow down and consider the light around you, which can ultimately help you become a better photographer. This may sound like a surprising thing to say in a book about flash photography, but the goal of any photographer should be to use whatever tools are appropriate to get the best shot.

2

Why are the backgrounds of my flash photos pitch black? It looks like I was in a cave!

In P (Program) mode, and all flash-using icon modes except for night mode, Canon EOS cameras assume that the flash is going to be the primary light source for the foreground subject. The camera is programmed to use a brief shutter speed (short exposure time) in these conditions.

However, if the ambient light levels are low, such as at night, the background will turn out very dark. This is because the flash can’t illuminate the background; additionally, the shutter speed is too short to expose adequately for those background areas.

The light from any battery-powered flash unit is always limited: you can’t expect to light up the Grand Canyon or the Eiffel Tower. Only subjects in the foreground, or near to the background, such as in a small room, are going to be lit. Simply cranking up the power of an on-camera flash unit won’t help bring up the background, since that will cause the near foreground to be overexposed.

To avoid the problem of black backgrounds, you will need to take the photo in Av, Tv, or M modes, as described in section 6.6, or use a second flash unit to light the background separately.

3

Why does the camera set a really slow shutter speed when I use a flash? Parts of my photos look sharp, but there’s weird fringing.

This situation is the reverse of the previous question. It happens when you take a flash photo in low-light conditions and the camera is in Av (aperture priority) mode or the night icon mode.

In Av, night, and Tv (shutter speed priority) modes, the camera meters the ambient (existing) light, and then fills in the foreground subject using flash. It doesn’t assume that the primary light source is the flash unit, and so the shutter speed it sets is the same as if you weren’t using flash at all.

In low light, this results in very long shutter times. If the shutter speed is very long, you’ll need a tripod to avoid motion blur during the exposure. If something in the photo, such as a person, moves during the shot, then you’ll end up with a double exposure. The flash-illuminated person will appear sharp and crisp, but the person will also be illuminated by ambient light, leading to ghosting or fringing. This can be desirable in some cases, as it lends a sense of motion, or it can just look like a smudgy mess.

Alternatively, you can switch to full auto (green rectangle) or P (Program) modes, which automatically expose for the flash-illuminated subject and not the background. These modes try to ensure that the shutter speed is high enough to let you handhold the camera without a tripod. The drawback of P and full auto modes is described above—dark backgrounds under low light conditions.

4

Why are the eyes of my friends and family glowing an evil red?

This is the “redeye” effect, a common problem with flash photography. It’s caused by white light from the flash unit reflecting off the red blood vessels lining the interior of the eye. “Greeneye” in cats and dogs is similar, though with a different underlying cause.

The easiest way to minimize photographic redeye is to use an external flash unit rather than a built-in flash, and reflect (“bounce”) the light from the flash unit off a wall or ceiling. For more detail, consult section 9.8.

If, however, the evil glowing eyes are visible in real life and not just in your photos, then you should probably consider arranging an exorcism. Contact a tabloid first if you want to exploit the situation to your financial advantage.

5

Why won’t my camera let me set a high shutter speed when I turn on my flash?

Each camera model has a maximum shutter speed that can be used with flash. This is known as the flash sync or maximum X-sync speed, and it varies from 1/90 second on older low-end cameras to 1/500 sec on one pro model. If you set a high shutter speed (say, 1/2000 sec) and you turn on a built-in flash unit or a Speedlite, the camera will automatically bring your shutter speed down to the X-sync value.

The maximum shutter speed when flash is used is always lower than the maximum shutter speed of an EOS camera, for complex mechanical reasons described in section 7.10. The X-sync value can be circumvented if your camera and flash unit both support high-speed sync (section 7.12).

6

I have an old flash unit. Will it work on my new Canon EOS digital camera?

Maybe. It depends on what type of flash unit you have and how you want it to work.

Canon EOS digital cameras work automatically with Canon Speedlite flash models ending in EX. However, if your Canon flash unit has a model name that ends in E or EZ or anything else, then its automated features will not work with EOS digital. It will fire at full power only, or not fire at all, depending on the camera.

As for flash units manufactured by other makers, check the specifications to see there’s support for “E-TTL flash metering.” If not, or if only “Canon TTL flash metering” is listed, then the unit probably won’t work automatically with a digital body (see section 7.2.2).

Some flash units have manual output controls, which let you specify the flash unit’s power output by hand. While this sounds limiting, manual flash as described in chapter 10 is actually a great way to light a scene.

If it’s a very old flash unit (pre-1980 or so), or if it’s a large studio flash unit that runs off AC power, it’s worth confirming that its trigger voltage won’t destroy your camera (see section 10.5).

7

I took two flash photos in rapid succession. Why is the second one totally dark?

All flash units take a number of seconds to charge up between flash bursts; the cycle time. If your second photo is dark, it probably means that your flash unit hasn’t had time to recharge after the first burst. You’ll need to wait for the unit to charge back up (and the pilot light on the back goes on) before taking the second photo.

Some flash units have “Quick Flash” ability that lets them fire when only partially charged. If your flash can do this, then you still probably took the second photo too quickly; the flash unit didn’t have enough time to recharge to an adequate power level but tried to fire anyway.

Different types of batteries charge up the flash at different speeds, so you might want to consider your battery options. To achieve a more rapid cycle time, external battery packs (section 12.12) are often used by wedding and news photographers. Note also that if your camera has a small built-in flash, it probably recharges more quickly than an external unit.

8

Why are my photos dark when I use a Speedlite EX or built-in flash to trigger my studio flash equipment?

The short answer is that manual flash metering (flash output set directly by the photographer) is not compatible with automatic flash metering (flash output controlled by the camera). You can’t reliably mix and match the two when optical slave triggers are used.

The slightly longer answer is that Speedlite EX flash units, when operating in E-TTL mode, send out at least one brief flash of light before the actual scene-illuminating flash. This “preflash” will prematurely trigger the optical sensors used by most studio flash units and optical slave devices. Consequently, since the light from the studio gear will have faded by the time the shutter opens, the resulting pictures will be too dark. For more details, consult section 11.7.3.

In this shot, E-TTL prefire triggered the studio flash too soon. The camera has recorded the reddish tail end of the slave flash unit concealed inside the antique camera’s flash bulb. See pages 20–21 for what this photo is supposed to look like.

9

Why use flash at all? Why not just use a fast lens and a high ISO?

As digital cameras improve and their image quality at high ISO settings becomes less noisy, this question becomes even more relevant. Why not shoot at f/1.8 with, say, ISO 3200? There are a number of reasons you might want to consider using flash, and a number of reasons you might want to avoid it.

Shooting at wide apertures like f/1.8 means that the depth of field (DOF)—the area of the image in sharp focus—will be very, very shallow, especially with a longer lens. If more than one person appears in the photo, for example, it will probably be possible to get the eyes of only one person in focus. If people are moving around, such as at a wedding, it probably won’t be possible to nail accurate focus with such a shallow DOF.

Shooting with a high ISO means that the picture will be noisier. Most digital cameras have grungy speckled “noise” at high ISO settings, which can mar the appearance of the photo.

Finally, with flash you have total control over the lighting. Available lighting is great, but there are times when the ability to specify precisely what light goes where can be very valuable. In a sense, this is about building a photo rather than finding it.

10

Why do my flash photos look so lousy? Do I need to buy a better camera or a more expensive flash unit?

Camera advertising often suggests that modern, fully computerized flash has the magic ability to let even inexperienced photographers take amazing photos. However, while automated flash has taken a lot of the drudgery and guesswork out of using flash, it hasn’t eliminated the need for good technique.

The first step in improving flash photography is to understand the nature of lighting. On-camera flash originating from a small light source is usually going to make hard-edged, harsh, and unflattering photos. That’s what most people think of when they think of flash.

The first step is to move the flash unit off the camera or to use multiple flash units. The second step is to start experimenting with light-modifying tools such as diffusers, softboxes, umbrellas, and filters. These are ways of improving the quality of light so it’s no longer just a harsh, blue-white beam emitting from the top of the camera.

While much of this book focuses on automated flash, this is often just the beginning. Most of the best flash-illuminated photos out there are taken by experienced photographers using purely manual equipment.