Canon EOS flash system
's EOS flash system refers to the photographic flash equipment and automation algorithms used on Canon's film or digital EOS single-lens reflex cameras. The line was first introduced in 1987. It has gone through a number of revisions over the years, as new flash exposure metering systems have been introduced. The main light-metering technologies are known as A-TTL, E-TTL, and E-TTL II.
The EOS flash system is capable of wireless multiple flash control, whereby a master flash unit IR or RF transmitter mounted on the camera body can control up to 3 or 5 groups of flash units. The Canon EOS 7D is the first Canon body to be able to control Speedlites wirelessly without the use of a Master Speedlite or IR transmitter; four other EOS models, the 60D, 600D, 650D, 70D, and 700D, also have wireless flash capabilities. The 7D is capable of handling three slave groups. The other cameras can handle two slave groups.
Metering systems
Canon has introduced several different metering systems for its flash products: A-TTL, E-TTL, and E-TTL II. Each system represents different approaches to achieving the proper flash exposure.A-TTL
Advanced-Through The Lens is a through-the-lens metering system that was expanded to support flashes. A sensor inside the camera reads the amount of light being reflected off 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, is a flash exposure system that adds a brief preflash during exposure metering when the camera is in the programmed exposure 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 thus 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.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, 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 and is barely perceptible, although it can be seen if you watch carefully for it. The pre-flash may cause undesirable reactions from 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, the pre-flash is fired when FEL is activated.
E-TTL has two major disadvantages over A-TTL when used with film cameras. One, since it takes its readings using the same sensor the camera uses for ambient metering, which is located above the prism in the viewfinder assembly, it cannot meter during exposure as the raised mirror prevents light from reaching the metering sensor. This means the flash cannot be quenched during the exposure, which can lead to overexposure if the lighting changes while the shutter is open, e.g. from a mirrored surface moving to reflect light directly back into the lens or another camera's flash going off at the same time. Two, since the E-TTL algorithm assumes the subject to be metered is positioned under an AF sensor and biases the exposure calculation to that sensor's location in the frame, it can choose settings that do not take into account the brightness in other areas of the image, resulting in overexposure if the selected AF sensor covers an area of low reflectance, or underexposure if the selected sensor covers an area of high reflectance that results in a bright specular highlight.
E-TTL II
E-TTL II is a software improvement on E-TTL and is now a standard in all EOS cameras introduced with or after the Canon EOS-1D Mark II in 2004. E-TTL II is implemented in the body, not the flash unit, and therefore can use existing E-TTL flash units and EF/RF 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 the old E-TTL system would normally be thrown off. Such improvements are possible because E-TTL II incorporates lens-to-subject distance information in its calculation to assist in determining an approximate guide number for flash output. The flash metering system is also no longer linked to the AF system, whereas in 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, in conjunction with subject distance information if available. This gives the photographer the flexibility to lock focus and recompose the scene without fooling the flash metering system. "Hot spots" that would normally throw off the flash metering system with systems such as E-TTL are also ignored in the calculation.
Speedlite products
Speedlite is the trade name for Canon's line of external flashes for use with their EOS line of cameras. It is similar but not to be confused with Nikon Corporation's "Speedlight" brand for their flashes. The Speedlite name is also used by Ricoh for its unrelated product line of flash units, such as the Ricoh Speedlite 202.The Speedlite name is intended to indicate that strobe flashes produce much shorter and more intense bursts of light than earlier photographic lighting systems, such as flashbulbs, or the continuous lighting used in some studio situations.
The model number indicates the guide number in decimeters, EG, the 430EX has a guide number of at 100ISO.
90 series flashes
90EX
Introduced in autumn 2012, the Speedlite 90EX is a very small unit designed specifically for the company's first mirrorless interchangeable-lens camera, the EOS M. It runs off two AAA batteries, and can serve as a wireless flash controller. At introduction, the 90EX was bundled with all EOS M kits sold in the EU, though not in the U.S.100-series flashes
160E
The Speedlite 160E was a compact basic flash with a guide number of, introduced in 1988 to accompany the EOS 750/850. It is unique among Speedlites in being powered not by AA alkaline batteries, but by a 2CR5 lithium photo battery. It was replaced in 1990 by the 200E.200 series flashes
200E
The Speedlite 200E was a minor upgrade to the 160E, bumping the output to GN and taking regular AA batteries.220EX
Introduced in 2000, Speedlite 220EX is a compact entry-level flash unit with a guide number of 22 m. It operates with four AA batteries, and does not feature any wireless capabilities.270EX and 270EX II
Speedlite 270EX and 270EX II are compact entry-level flashes with a guide number of 27 m.270EX features a zoom head which covers 28–55 mm lenses and bounce head capability. 270EX II adds wireless slave mode and remote shutter triggering.
300 series flashes
300EZ
The Speedlite 300EZ was a compact zoom flash released at the introduction of the EOS system in 1987 with the EOS 650. It has a guide number of, takes 4 AA batteries, and incorporates automatic zooming of the flash head to match the angle of illumination to EF lenses in the range of 28 to 70mm. It also has a visible-light auxiliary AF illuminator which projects a pattern of red lines on the subject to aid autofocusing in dark environments.320EX
In 2011, Canon introduced a new flash that has a built-in LED light. One reviewer noted that the flash occupied a completely new niche in the Canon flash lineup, "slotting between the 270EX II and the 430EX II", and added that it did not replace a previous model.The LED can be used as a spotlight to see objects in dim light before taking a photo, but is mainly present to provide fill light for video shooting. The aforementioned reviewer also stated that the LED could be used in some situations as a substitute for a standard flashlight.
380EX
This unit is very similar to 430EX in terms of E-TTL functions and power levels. It does not feature an LCD screen like 400 series systems but has several LEDs indicating zoom position and other functions. It is the first E-TTL unit from Canon sold as a dedicated flash for the first E-TTL cameras - EOS 50 and EOS 50e, which were introduced in 1995.400 Series Flashes
Canon's external flashes with model numbers in the 400 range tend to be their mid-range external flashes. They all tend to have the ability to adjust the direction of the flash via a swivel head, which allows 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 400 series differs from the higher end 500 series mostly by lacking a remote controller.420EX
The Speedlite 420EX is an external flash formerly made by Canon. The Speedlite 420EX is one of Canon's older mid-range flashes, being replaced by the 430EX in 2005. It was primarily intended for users wanting to step up from the entry-level flashes, as well as for use as a slave flash along with the more advanced Speedlite 550EX flash.Compared to its predecessor, the 380EX, it provided slightly more power, an improved autofocus assist beam, tilt and swivel, and the ability to serve as a slave in Canon's wireless multiple-flash system. Like the 380EX, the 420EX did not provide user controls ; any flash-related settings, such as exposure compensation or second-curtain synchronization, had to be set using the body.
Its autofocus assist system was designed to cover Canon's autofocus layouts with between 1 and 7 autofocus points; it was not designed to cover the 45-point autofocus layout used by higher-end bodies. It used two lamps to project horizontal and vertical patterns, which matched the line sensitivity of the autofocus sensors used in those autofocus layouts. Either or both patterns would be projected depending on the body being used and the user's selection of autofocus sensor.