A speed light is a common term used to describe an accessory electronic camera flash. Depending on the manufacturer, it might be spelled “Speedlite” or “Speedlight” and may also be referred to as a “flashgun,” which is a term that goes back to the days of scrappy newspaper reporters with Speed Graphics and flashbulbs. Some people simply call it a “flash.”
Nomenclature aside, speed lights allow you to take sharp, daylight-balanced pictures in dark environs in both color and black and white. Speed lights are also handy for “opening” shadow areas when photographing outdoors in contrasty or backlit conditions (time to break out the fill flash), as well as having an uncanny knack for freezing fast-moving subjects.
Your camera’s built-in flash is sufficient for quick snapshots and the sort, but party pics aside, it has its limitations in terms of power output and creative flexibility.
For starters, speed lights output more light than built-in flash. Even the smallest accessory speed lights output anywhere from a half to a full stop more light, and the larger models can output two to three additional f/stops of light than the average pop-up flash. This additional light output makes it possible to shoot at smaller apertures for greater depth of field. The additional power output also makes it possible to light up larger areas.
Most mid- to full-size speed lights also feature flash heads that tilt or swivel, which enables you to bounce the flash output from adjacent walls or ceilings, resulting in a softer, more flattering light than the harsher, dead-on light you get from direct flash. Because the flashtubes in speed lights are positioned further away from the lens axis, you’re less likely to have red-eye problems, even when shooting with the flash head aimed straight at your subject.
If your camera has a hot shoe, you can probably use a speed light with it. Even if your camera doesn’t have a hot shoe, depending on the make and model of your camera, there are often alternative methods of photo-slaving speed lights for use with cameras that don’t have hot shoes.
TTL is an abbreviation for “through the lens,” which means that the flash duration, or the amount of light emitted by the speed light, is determined by the reflective qualities of the subject as well as the distance of the subject from the camera position when viewed through the camera lens. As with ambient light readings, the most accurate method to determine the best flash exposure is by reading the reflective qualities of the scene as viewed through your camera’s lens.
With few, if any, exceptions, dedicated speed lights made by your camera manufacturer are TTL-enabled, and they will be labeled as such. Third-party speed lights, however, may or may not be TTL enabled and in some cases might perform in TTL mode only with specific make and model cameras. Some of the less expensive speed lights that do not have TTL capabilities more often than not feature auto thyristors that also measure reflectance, but with less precision than TTL models.
Technically speaking, any camera with a hot shoe will trigger any shoe-mount speed light regardless of who manufactured either component. The problem is that once you start mixing and matching components from different manufacturers, you more or less lose exposure control, which means even though the flash is firing there’s no way to determine how much (or how little) light is really striking your subject.
If you must use mismatched cameras and speed lights, you always have the option of setting the exposure manually using the exposure controls located on the back of the speed light. After eye-balling the results of a few test exposures on your camera’s LCD, you can establish correct flash exposures with relative ease.
Generally speaking, third-party speed lights are equal in performance to their OEM (Original Equipment Manufacturer) counterparts, and in some cases the third-party options have more features than OEM speed lights.
The differences invariably have to do with light output, whether or not the flash head swivels or tilts, power options (if any), and the number of accessories to complement the basic flash unit.
Guide numbers represent the illuminating power of your flash unit, with a higher guide number representing a more powerful device. Guide numbers are usually expressed in relation to 100 ISO film speed, and the formula to determine this number is GN = subject distance x by f/stop number. Conversely, you can determine which aperture to use by dividing the guide number of your flash by the distance between your flash and subject matter. If you have a flash unit with a guide number of 80' (24.4m) and are photographing a subject at 10' (3m), you would use f/8 to achieve a proper exposure (80/10 = 8).
In a bid to make their speed lights appear more powerful than they in fact are, some manufacturers calculate the guide number of their products based on the output with the flash head set to the telephoto position. What this means is when comparing guide numbers of competitive speed lights, check the fine print to establish which focal length setting was used to establish the output data.
Your camera’s flash sync speed represents the fastest shutter speed you can set your camera to before you start “clipping” the exposure, or not exposing the entire picture area to the flash portion of the total exposure. When you clip your flash exposure with a faster shutter speed than the camera’s sync speed, it will show up as a darker or non-exposed area along one edge of the frame (depending on the camera’s shutter mechanism), which failed to record the full duration of the flash because the entire sensor or frame of film was not exposed at precisely the same time of the flash burst. With slower shutter speeds, there is more time for the entire shutter to open and the flash to fire, before the shutter closes again. Depending on your camera, the sync speed usually varies from 1/125-second for entry-level DSLRs to 1/250 to 1/320-second for pro DSLRs.
Depending on the make and model of your camera/flash system, flash sync speeds of up to 1/8000-second are often possible when photographing with your speed light in manual or HP mode. See your camera and flash manuals for details.
Zoom heads are useful because they enable you to optimize the angle of the light emitted by your speed light to match the angle of view of the lens you are using. This means when shooting with a wide-angle lens, the zoom head pulls back to allow the light to spread across a wider field. Likewise, when shooting with a longer lens, the head zooms in to concentrate the light to fill a narrower field.
Another advantage of a zoom head is that as the flash head zooms in tighter, it requires less output to light the narrower viewing area, which speeds up recycling times and extends battery life.
Depending on the make and model, some speed lights have auto zoom heads that automatically zoom in or out as you zoom your lens in or out. Less expensive speed lights have to be zoomed in or out manually to achieve the same effects.
Speed lights require their own power sources, usually in the form of AA batteries or battery packs.
Many speed lights allow you to attach external power packs, which depending on the make and model of the speed light, are either tethered packs containing additional AA batteries, or rechargeable battery packs that enable you to shoot hundreds of exposures with far shorter recycling times than the speed light’s standard power supply.
There are also several third-party power supply manufacturers that make units that will power both your camera and flash.
In addition to external power supplies, accessories worth considering when purchasing a speed light include: