This unit combines a high guide number with E-TTL flash metering. However, it is when two or more Speedlite 550EX units are used together that you realise the major advances being made in flash photography for EOS cameras.

The 550EX is designed to be used in a wireless control mode. This allows one gun to be designated as the master unit and up to three groups of guns to be remotely controlled from this master unit. Studio-type lighting can be created while retaining the advantage of a fully dedicated flash system.

The main components of the system are the Speedlite 550EX flash and the Speedlite Transmitter ST-E2. The 550EX can be used as a master flash, remotely controlling up to three groups of additional flashguns from the camera.

The Speedlite transmitter, used on camera in place of a Speedlite, has more limited capabilities; it can control just two remote groups of flashes.

If you use the Speedlite 550EX as the master unit there is no limit to the number of flashguns that can be used in the flash groups. Ratio control can be applied to groups A and B. Group C, intended for ‘accent’ lighting, does not have ratio control. However, flash compensation can be used to control the brightness of the illumination from Group C, effectively giving total control of the lighting from all three groups.

EOS magazine, December 1998, page 39

Type: Direct-sync, shoe-mount flash with E-TTL/TTL autoflash control and wireless transmission/reception (E-TTL preflash, AF-assist beam, auto zoom, and bounce flash).
Compatible cameras: Type-A EOS cameras (for E-TTL autoflash control)
Type-B EOS cameras (for TTL autoflash control)
Flash duration: 1.2ms or less. For quick flash: 2.3ms or shorter
Flash coverage:
• auto zoom head covers 24mm, 28mm, 35mm, 50mm, 70mm, 80mm and 105mm lens focal lengths automatically
• manual zoom: enabled with zoom button
• wide panel: when the built-in wide panel covers the flash head, flash coverage is extended for 17mm lens focal length
Flash modes:
• normal flash
• quick flash
• high-speed sync (FP flash)
• stroboscopic flash: 41 flash frequency settings, 31 firing settings
• preflash: obtains exposure reading for E-TTL autoflash control
• test flash: with test firing button
• modelling flash: fired with the EOS-3’s depth-of-field preview button
Bounce positions:

Exposure control modes:
• E-TTL autoflash (with Type-A cameras: Preflash evaluative metering)
• FE lock (with Type-A cameras
• TTL autoflash (with Type-B cameras: Off-the-film metering)
Flash exposure compensation:
• automatic flash output reduction for fill flash
• flash exposure compensation adjustable manually with the speedlite up to 3 stops in 1/3- or 1/2-stop increments
• flash exposure compensation adjustable manually up to 3 stops in 1/3- or 1/2- stop increments with cameras equipped with flash exposure compensation function
FEB: set with the speedlite up to +/ - 3 stops in 1/3-stop or 1/2-stop increments
Flash range (with 50mm f1.4 lens at ISO 100):
• with normal flash: 0.5 - 30 meters / 1.6 - 100 feet
• with quick flash: min. 0.5 - 7.5 meters and max. 0.5 - 21 meters
: min. 1.6 - 25 feet and max. 1.6 - 70 feet
• with high-speed sync: 0.5 - 15 meters / 1.6 - 49 feet (at 1/250 sec.)
Flash exposure confirmation: yellow-green pilot lamp lights
Flash-ready indication:
• red pilot lamp indicates normal flash ready
• yellow pilot lamp indicates quick flash ready
AF-assist beam linkage and range: linked to area AF (45 focusing points), effective from approx. 0.6 to 10 meters / 2 to 33 feet at the centre and 0.6 to 5 meters / 2 to 16 feet along the periphery (in total darkness)
Wireless functions
Transmission system:
optical pulse transmission
Configuration: camera, master unit, and slave unit(s)
Wireless switch over: with wireless selector
Wireless selector positions: OFF, master, slave
Channels: 4
(Master unit)
Transmission angle:
horizontal: approx. 80 / vertical: approx. 60
Transmission range: indoors: approx. 12 to 15 meters / 39.3 to 49.2 feet
outdoors: approx. 8 to 10 meters / 26.2 to 32.8 feet
No. of transmissions: approx. 1500 (without master unit firing)
Controllable slaves: A, B, C (3 groups)
Flash control:
• E-TTL autoflash (with Type-A cameras)
High-speed sync (FP flash) / FE lock / flash exposure compensation / FEB / flash ratio control
• manual flash (with Type-A and B cameras)
• stroboscopic flash (with Type A and B cameras)
Flash ratio control: A:B = 8:1 to 1:1 or 1:1 to 1:8 (in thirteen 1/2-stop increments)
(for C, flash exposure compensation can be set up to 3 stops in 1/3 or 1/2-stop increments)
Master flash: ON/OFF possible (when ON, automatic set as slave unit A)
(Slave unit)
Reception angle:
horizontal: approx. 80 / vertical: approx. 80
Flash coverage: set automatically to 24mm (manual zooming of flash head also enabled)
Flash-ready indication: AF-assist beam emitter blinks
Flash modes:
• controlled automatically by master unit
• manual flash and stroboscopic flash settable independently from master unit
Flash exposure compensation: settable individually with each slave unit up to 3 stops in 1/3- or 1/2-stop increments
Slave operation confirmation: enabled with master unit’s test firing button
Slave unit SE mode cancellation: while the slave unit’s SE mode is in effect, the slave unit turns on when a flash is fired.
The slave unit’s SE mode can be cancelled by the following wireless operations:
• when the master unit’s test firing button is pressed
• when the camera’s FE lock button is pressed
Power source: internal power sources:
• size-AA alkaline LR6 batteries (6 V) x 4
• size-AA Nicad KR15/51 batteries x 4
• size-AA lithium FR6 batteries (6 V) x 4
External power sources:
• compact battery pack CP-E2
Size-AA alkaline LR6 (AM-3) batteries (9 V) x 6
• transistor pack E
Battery magazine TP with size-C alkaline LR14 (AM-2) batteries (9 V) x 6 Ni-Cd pack TP (NR-SC Ni-Cd batteries x 6 in sealed pack)
SE mode: with the power switch set to SE, the speedlite enters the SE mode as follows:
• on-camera master unit enters the SE mode after 90 sec. of non-use
• slave unit enters SE mode after 60 min (or 10 min. with CF-4) of non-use
Custom functions:

Dimensions (mm) and weight: 80 (W) x 138 (H) x 112 (D), 405g


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