Flash Work EOS/EOS DIGITAL + SPEEDLITE
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Flash Terminology
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Flash Terminology
Ambient exposure compensation Ambient light Autoflash metering
Bounce flash Catchlight Clip-on flash
Diffusing Exposure compensation FE (Flash Exposure) Lock
FEB (Flash Exposure Bracketing) Flash Flash exposure compensation
Guide Number (G No.) High-speed sync Intermittent flash
Main flash Modeling flash Multiple flash (wireless and wired)
Normal flash Preflash Recycling time
Red eye Slave unit Stroboscopic flash
Synchronization White balance Wide panel
X-sync Dustproof, water-resistant design  
Ambient exposure compensation
A function for adjusting ambient exposure through aperture and shutter speed and without adjusting flash output. This function affects both foreground and background brightness and is useful for brightening the background during fill-in flash photography.
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Ambient light
All light in the shooting environment from natural and artificial sources (such as tungsten light, fluorescent light and candle light), excluding light provided by the photographer via flash units.
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Autoflash metering
The camera's light sensor meters the light reflected by the subject after the flash begins firing. The flash output is then controlled instantly so that the proper flash exposure is obtained.
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Bounce flash
Light bounced off a ceiling, wall or other surface to soften the light hitting a subject. A white or light-colored surface is best since the color of the reflective surface affects the color of the light. Bouncing the light also lowers its brightness in comparison to direct flash, requiring adjustments to aperture or ISO speed settings.
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Catchlight
Light that reflects in a subject's eyes and adds life to the portrait. Either a flash or reflector panel is used to create catchlight.
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Clip-on flash
Any flash unit that can be attached to the accessory shoe of a camera.
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Diffusing
Spreading and softening flash illumination by using a translucent material placed between the flash unit and subject or bouncing the flash off a ceiling or wall. Soft diffused light naturally lightens the shadows and makes flash photography with softer contrast possible.
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Exposure compensation
A function for adjusting ambient exposure through aperture and shutter speed. Since the flash output is automatically controlled by the aperture, no flash exposure compensation is applied. To compensate flash exposure, use the flash exposure compensation function.
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FE (Flash Exposure) Lock
When the photographer locks the focus, this feature locks the flash level (determined by spot or partial metering) by firing a preflash and storing the appropriate flash output level so that the ideal exposure will be maintained for the main subject even if the scene is reframed. In flash photography, this feature is useful for obtaining the proper exposure by metering at a certain spot or subject in the frame.
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FEB (Flash Exposure Bracketing)
A feature that automatically produces three shots with different flash output (correct exposure, underexposure, overexposure). Background exposure is unchanged since the aperture and shutter speed are not adjusted.
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Flash
A flash is a short-duration, brilliant burst of light.
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Flash exposure compensation
This function only adjusts the level of illumination provided by the flash. It's particularly effective for fine-tuning the balance between foreground and background exposure during fill-in flash, but it can also be effective at compensating for highly reflective and non-reflective subjects.
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Guide Number (G No.)
A number indicating the amount of light a flash emits. Its relation to the aperture and the distance between the flash head and subject is as follows:

G No. /Aperture (f) = Distance for optimal exposure
G No. /Distance = Aperture (f) for optimal exposure
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High-speed sync
In normal flash photography, the flash is synchronized to fire at the moment when the first curtain finishes traveling and before the second curtain starts traveling. High-speed sync extends the flash duration, making flash synchronization possible when using fast shutter speeds that form a slit between the first and second curtains while traveling. EOS dedicated EX Series Speedlites offer this feature, enabling automatic high-speed sync control with E-TTL II.
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Intermittent flash
Simulating a longer-lasting flash by repeatedly firing the flash unit(s) at high speed. This technology is used for high-speed sync and modeling flash.
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Main flash
The principle flash fired after the preflash when the shot is actually taken.
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Modeling flash
A monitoring flash that can be fired before photographs are taken to help determine light placement for desired light balance, shadows, etc.
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Multiple flash (wireless and wired)
This is a flash setup with one or more Speedlites other than the one attached to the camera. In a wired system, multiple Speedlites are connected with a multi-Speedlite connector and extension cords. In a wireless or slave unit system, multiple Speedlites can fire without any wired connections. Speedlite 580 EX II and 580EX are equipped with both transmitting and slave functions. With a Speedlite Transmitter ST-E2 or Speedlite 580EX II, 580EX, MR-14EX, or MT-24EX set as the master unit, multiple Speedlite 580EX IIs, 580EXs or 430EXs (set as slave units) can be wirelessly controlled for E-TTL II autoflash.
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Normal flash
A normal flash is a short-duration flash of 1/200 sec. or less that illuminates the subject but leaves the background underexposed. See "ambient light" for comparison.
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Preflash
This is the low-output flash fired before the main flash is fired in synchronization with the shutter. It is used for measuring the subject distance and evaluative metering. A preflash is also fired when using FE lock.
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Recycling time
Speedlites use a capacitor to store electrical energy for the high voltage required by the flash. When a flash is fired, the capacitor is discharged and then recharged for the next flash. The recycling time is the time it takes the capacitor to recharge after firing.
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Red eye
This refers to the red dots in the eyes of the subject in a photograph taken with a flash. It is prone to occur when the person's pupil is wide open (in low light), the flash is mounted near the camera lens, and the flash reflects off the retina's red capillaries. With red-eye reduction, an incandescent lamp shines or a preflash is fired to shrink the pupil's diameter and lessen the likelihood of red eye.
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Slave unit
This is a flash unit that fires in response to the firing of a master flash unit. For example, Speedlite 580EX IIs, 580EXs, and 430EXs can be used as slave units that fire when high-speed pulses are received from a Speedlite Transmitter ST-E2 or Speedlite 580EX II, 580EX, MR-14EX or MT-24EX set as a master unit.
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Stroboscopic flash
This is a series of flashes fired in a single burst while the shutter is open. Stroboscopic flash is effective for capturing the movement (for later analysis) of a moving subject against a dark background.
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Synchronization
Firing of the flash at the moment the first and second shutter curtains are fully open.
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White balance
A function in digital cameras that allows colors to be corrected, based on the color temperature of the light source, to ensure faithful color reproduction. Auto white balance, selectable pre-set white balance modes for different light sources, and manual white balance settings are provided. The preset daylight mode provides warm colors in incandescent light and a bluish tint in fluorescent light or shade. The color temperature of a flash is almost the same as sunlight.
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Wide panel
A translucent panel that extends flash coverage when fitted to the flash unit's light-emitting component. Speedlite 580EX II, 580EX and 430EX include a built-in slide-type wide panel.
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X-sync
This is an electrical contact that enables the flash to fire when the shutter is fully open. In SLR cameras equipped with a focal-plane shutter, the x-sync speed is the fastest shutter speed at which the first and second shutters are fully open.
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Dustproof, water-resistant design
Outdoor photo shoots expose camera equipment to various risks. For example, an unexpected rainstorm or sandstorm might spray the camera with water or dust that could cause a malfunction if it penetrated the body. To prevent such problems, the EOS-1D Mark III features a dustproof, water-resistant design with rubber sealing where panels meet and where buttons and dials join the body. Such measures are also applied to various Canon accessories including the Speedlite 580EX II, CP-E4 Compact Battery Pack, and OC-E3 Off-Camera Shoe Cord. Users can therefore build entire systems that are highly resistant to water and dust.
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