Canon EOS flash system
Advanced-Through The Lens (A-TTL) is a through-the-lens (TTL) 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.
[1] The amount of light returned from this preflash is used to determine an appropriate tradeoff between aperture and shutter speed in P mode.
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) thus causing inaccurate settings.
[1] 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.
Such improvements are possible because E-TTL II incorporates lens-to-subject distance information in its calculation (with lenses that communicate distance information to the camera body)[3] to assist in determining an approximate guide number for flash output.
This gives the photographer the flexibility to lock focus and recompose the scene without fooling the flash metering system.
[5] 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.
The Speedlite 200E was a minor upgrade to the 160E, bumping the output to GN 20 m (66 ft) and taking regular AA batteries.
[9] Introduced in 2000, Speedlite 220EX is a compact entry-level flash unit with a guide number of 22 m (at ISO 100).
[12] It has a guide number of 30 m (98 ft), 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.
[13] 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.
It does not feature an LCD screen like 400 series systems but has several LEDs indicating zoom position and other functions.
The 430EX II[19] was announced on June 10, 2008[21][22] and improved on its predecessor by adding a stronger, all metal foot with quick release mechanism, silent flash recycling, 20% shorter recycle times and support for setup through the camera's menu system.
The Speedlite 470EX-AI is an external flash made by Canon for use with their EOS line of cameras that was announced on February 25, 2018.
Key features of the 580EX II that make it desirable are a built-in PC terminal, easy locking metal foot, faster recycling time, silent charge, a much easier-to-use battery cover and support for setup through the camera's menu system.
However some better features on the earlier model were dropped like EL backlight on the LCD (580EX II uses simple led back-light) and designated master/slave switch.
Countries that are not listed include: the Republic of South Africa, Israel, Argentina, Pakistan, to name but a few.
It weighs only 190g (without batteries) while providing full swivel and bounce support as well as ability to control other Speedlite flashes in master mode.
[35] The Speedlite EL-1 was announced in October, 2020, and released in February, 2021, replacing the 600EX II-RT as Canon's flagship flash.
New features include rechargeable Li-ion Battery Pack (LP-EL), upgraded Xenon Flash tube and internal cooling system, as well as dust- and water-resistance of the same standard as found on Canon's EOS-1D camera.
[36] It allows for multiple off-camera flashes to be fired in E-TTL mode without the need for connecting wires.
[32] It features a new bi-directional 2.4 GHz wireless communications with a range of 30m, but does not control the older IR-based Speedlites.
The ST-E3-RT II was introduced February 4, 2021 and brings control over 2nd-curtain sync, support for the Speedlite EL-1’s low-power 1/8192 micro flash, and FE memory which saves E-TTL settings for further manual adjustment.
[39] The ST-E10[40][41] was introduced in September, 2021 along with the EOS R3, as a small, lightweight radio flash controller for cameras having the Multi-Function Shoe.
Canon currently produces three flash products for macro photography RF slave and master.
