Talking about the Canon EOS Flash System

Canon Speedlite 430EX flash with table stand.Canon Inc.'s EOS flash system the photographic flash mechanism used on Canon's EOS single-lens reflex cameras, whether 135 film or digital, from their 1987 introduction until the present day has gone through a number of revisions over the years, as new flash exposure metering systems have been introduced. The main technologies are known by the names "A-TTL", "E-TTL", and "E-TTL II". These technologies involve both the EOS camera bodies and the flash units themselves, which are sold under the trade name of Speedlite (similar but not to be confused with Nikon Corporation's "Speedlight" brand for their flashes). The EOS flash system is capable of wireless multiple flash control, whereby a master flash unit or IR transmitter mounted on the camera body can control up to 3 groups of flash units through infrared (IR) signals. The Speedlite name is also used by Ricoh for its unrelated product line of flash units. For example, the Ricoh Speedlite 202.

A-TTL

A-TTL is an initialism that stands for Advanced-Through The Lens flash metering. As with ordinary TTL flash exposure systems, a sensor inside the camera reads the amount of light being reflected off of the film during the exposure. When the sensor determines that the exposure is sufficient, it terminates the flash pulse. A-TTL, first seen on the T90 (which predates the EOS family), is a flash exposure system that adds a brief preflash during exposure metering when the camera is in the programmed exposure (P) mode. The amount of light returned from this preflash is used to determine an appropriate tradeoff between aperture and shutter speed in P mode. Depending on the specific flash unit and whether or not it is set to bounce, the preflash might be infrared or it might be the normal white flash. In an A-TTL system the sensor that reads the preflash return is located on the flash unit; this caused some issues especially when using filters as the filter would cover the lens (but not the sensor outside the lens) As a result causing inaccurate settings. Some early Canon EOS cameras also used the A-TTL preflash in non-programmed exposure modes to detect "out of range" conditions; the "out of range" warning feature was dropped on later models, reportedly due to patent conflicts.

Canon Speedlite 580EX II.

E-TTL

E-TTL (Evaluative-Through The Lens) is a Canon EOS flash exposure system that uses a brief pre-flash before the main flash in order to obtain a more correct exposure. Unlike TTL and A-TTL metering, which use a dedicated flash metering sensor mounted in the base of the mirror box, E-TTL uses the same evaluative metering sensor used for ambient metering. Like TTL (and like the actual flash metering, but not the pre-flash, of A-TTL), the sensor is internal to the camera and takes its exposure via the lens so any filters added to the lens will also affect the E-TTL readings giving more accurate exposure information to the camera.

The pre-flash occurs immediately before the main flash (except when using the camera / flash in 2nd curtain synch mode) and is barely perceptible, although can be seen if you watch carefully for it. The pre-flash may cause undesirable reactions of animate objects. E.g., humans may blink as a reaction to the pre-flash, and have their eyes closed by the time the main flash occurs. When using flash exposure lock (FEL), the pre-flash is fired when FEL is activated.

E-TTL II

Basically a software improvement on E-TTL, E-TTL II is now a standard in all EOS cameras introduced with or after the Canon EOS-1D Mark II (2004). E-TTL II is body-dependent and therefore can use existing E-TTL flash units and EF lenses.

The main improvement of E-TTL II is that it gives a more natural flash exposure, by being able to handle tricky scenes where normally the old E-TTL system will be thrown off. Such improvements are possible because E-TTL II now incorporates lens-to-subject distance information in its calculation (where available) to assist in determining an approximate guide number for flash output. The flash metering system is also no longer linked to the AF system, where in the old E-TTL metering bias is given to the selected AF point. Rather, E-TTL II compares the ambient and the pre-flash light levels of the scene to determine where the subject lies. This gives the photographer flexibility to lock focus and recompose the scene without fooling the flash metering system. 'Hotspots' (areas of high reflectance) that will normally throw off the flash metering system are also ignored in the calculation.

Speedlights

Speedlite 430EX

The Speedlite 430EX is an external flash made by Canon Inc. for use with their EOS line of cameras. The Speedlite 430EX is Canon's current midrange Speedlite, first released in 2005 and designed to be a replacement for the Speedlite 420EX. It is compatible with E-TTL II flash metering. The 430EX's replacement, the Speedlite 430EX II, was announced on June 10, 2008. The flash's Guide Number is 141'/43m (at ISO 100 and 105 mm).

The Speedlite 430EX can be used as a wireless slave unit with Canon Speedlite Transmitter ST-E2 or top-of-line flashes with built-in infrared controller, such as Speedlite 550EX or Speedlite 580EX II

The flash head can swivel up (to 90), right (to 90) and left (to 180). The swivel properties allow the photographer to bounce the flash off walls, ceilings, and other objects, diffusing the light that hits the subject and reducing the harsh shadows associated with on-camera flash.

Speedlite 430EX II

The Speedlite 430EX II is an external flash announced by Canon Inc. for use with their EOS line of cameras. It was announced on June 10, 2008. It replaces the Speedlite 430EX. The flash's Guide Number is 141'/43m (at ISO 100 and 105mm). It is compatible with wide-angle lenses up to 14mm. The Speedlite 430EX can be used as a wireless slave unit with Canon Speedlite Transmitter ST-E2 or top-of-line flashes with built-in infrared controller, such as Speedlite 550EX or Speedlite 580EX II.

The flash head can swivel up (to 90), right (to 90) and left (to 180). The swivel properties allow the photographer to bounce the flash off walls, ceilings, and other objects, diffusing the light that hits the subject and reducing the harsh shadows associated with on-camera flash.

Speedlite 550EX

Canon Speedlite 550EX
Canon Speedlite 550EX
The Speedlite 550EX is a flash made by Canon Inc. for use with their EOS line of cameras. Until the release of the Speedlite 580EX in late 2004, the 550EX was Canon's top-of-the-line flash.

The 550EX flash features an infrared controller that enables wireless control of other flashes similar to the Speedlite Transmitter ST-E2.

The flash head can swivel up, right and left. The swivel properties allow the photographer to bounce the flash off walls, ceilings, and other objects, diffusing the light that hits the subject and reducing the harsh shadows associated with on-camera flash. The image shows the flash head in a vertical position.

Speedlite 580EX

Canon Speedlite 580EX II
The front of the Speedlite 580EX..

Canon Speedlite 580EX II
Canon Speedlite 580EX II

The Speedlite 580EX is a flash made by Canon Inc. for use with their EOS line of cameras. It was succeeded by the Speedlite 580EX II in early 2008.

The 580EX flash can act as a controller that enables wireless control of other flashes similar to the Speedlite Transmitter ST-E2.

Speedlite 580EX II

The Speedlite 580EX II is an external flash announced by Canon Inc. for use with their EOS line of cameras. It replaced the Speedlite 580EX in early 2008.

The 580EX II flash can act as a controller that enables wireless control of other flashes similar to the Speedlite Transmitter ST-E2.

The flash head can swivel up, right and left. The swivel properties allow the photographer to bounce the flash off walls, ceilings, and other objects, diffusing the light that hits the subject and reducing the harsh shadows associated with on-camera flash.

Both versions of the 580 EX utilize the new ETTL II technology. TTL (Through-the-lens metering) is a dynamic exposure control system intended to properly expose a scene. Electronic sensors contained beneath an SLR camera's mirror box monitor light reflected from a digital camera's imaging sensor to detect when a proper amount of illumination from a flash is given. As an exposure is made, the TTL electronics instruct the flash provide more or less illumination based on the reflected light.

In instances where a subject is too far from the camera to reflect an appreciable amount of light back to the camera, a TTL flash will typically expose the scene at full power. Subjects wearing black clothing may cause TTL flashes to overexpose the scene because the clothing is less reflective. Likewise a subject who is wearing all white may cause a TTL flash to underexpose the scene due to the highly reflective nature of the clothing. In either instance, the photographer may use flash exposure compensation settings to correct for clothing choices.

Key features of the 580 EX II that make it desirable are a built-in PC terminal, metal foot, faster recycling time and a single-button tilt/swivel similar to the Nikon SB-900.

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