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Speedlite Transmitter ST-E3-RT (Ver. 2)


Item Code: 5743B012AA



Updated to include Wireless Rear Curtain Synchronization, A Minimum Output Range of 1/8192, and FE Memory


When used in combination with the Speedlite EL-1, the Speedlite Transmitter ST-E3-RT (Ver.2) provides additional benefits* of wireless rear curtain synchronization so the flash fires as the shutter closes to capture beautiful light trails to signify movement of the subject, minimum flash power as low as 1/8192 for even more opportunity to work in low available light, and FE memory so you can store an E-TTL flash exposure and continue to use that same exposure when subjects and scenes remain unchanged.

• Manual flash power below 1/128th not possible with 600EX-RT series, and 430EX-RT used as receiver units.
• 2nd curtain sync can be used with Speedlite EL-1, 600EX-RT series and 430EX-RT receiver units, but with EOS R5, R6, or EOS-1D X Mark III cameras only.

Up to 5 groups, or 15 Individual Flashes can be Controlled via 1 Transmitter


The Speedlite Transmitter ST-E3-RT (Ver.2) facilitates radio controlled, two-way wireless transmission up to 98.4 feet, for a reliable and robust connection among sender and receiver units. Communicating on 2.4 GHz frequencies, the ST-E3-RT (Ver.2) does not have the same directional limitations of traditional wireless optical transmitters. Where other wireless signals can be interrupted by physical obstacles, radio controlled systems excel. Fifteen transmission channels are available, selectable manually or automatically (for optimum radio transmission, depending on environment), and radio transmission IDs can be set to prevent interference from other photographers on the same channel. With the extended, more reliable range afforded by radio transmission, ambitious photography is made easier.

Supports E-TTL II Flash, Manual Flash, Stroboscopic and Auto External Flash Metering

With the Speedlite Transmitter ST-E3-RT (Ver.2), up to fifteen Canon RT-compatible Speedlites in five groups can be controlled from the camera, via a single transmitter. Each group can be set to a different flash mode, enabling multiple configurations for creative photography. For example, with the ST-E3-RT (Ver.2) some flashes can be directed to operate according to the camera’s E-TTL flash reading, others can be set manually; groups can be set to overexposure or underexpose, and much, much more. With up to fifteen flashes under the control of one transmitter, wirelessly, complex lighting setups normally reserved for the studio are a breeze.

Dot Matrix LCD Panel Displays all Pertinent Information Simultaneously and Backlit Control Panel means Easy Operation

The Speedlite Transmitter ST-E3-RT (Ver.2) features a dot matrix LCD panel (172 x 104 dots). This LCD displays Flash status, flash settings and wireless configuration for any combination of Speedlite EL-1, 600EX-RT series, and 430EX-RT, used off-camera as Receiver units. With the transmitter’s LCD screen combined with backlit operation buttons and even an internal sound emitter, the ST-E3-RT (Ver.2) is as easy to operate in the dark as in daylight.

8 Types of Custom Functions, 3 Types of Personal Functions

To accommodate the demands of a number of different shooting situations, the Speedlite Transmitter ST-E3-RT (Ver.2) can be configured with eight different Custom Functions and any of three Personal Functions. Custom Functions include: auto power off, modeling flash controls, sound, illumination and more. Personal Functions include display contrast and LCD panel illumination color for both sender and receiver flashes.

High-Performance Hot Shoe Contacts for Reliable Information Transmission and Operation

The Speedlite Transmitter ST-E3-RT (Ver.2) is built to the standards one would expect from professional Canon camera systems. The hot shoe contact ensures reliable communication between camera and transmitter. Dust and water resistance is excellent as well: all moving parts and areas surrounding the transmitter’s display and buttons are sealed for uninterrupted performance in harsh conditions. A dust and water resistant design for the mounting foot creates a dust and water resistant seal between camera and flash. Compact and lightweight, the ST-E3-RT (Ver.2) is approx. 2.7 (W) x 2.4 (H) x 3.0 (D) in.




Radio transmissions wireless Speedlite transmitter

Compatible Cameras

Type A EOS cameras (E-TTL II/E-TTL autoflash)

Sync Speed

High-Speed Sync provided

Flash Exposure Confirmation

Flash exposure confirmation lamp lights in green*
* If it does not light, shooting is not performed with the standard exposure

FE Memory


Exposure Control

E-TTL II / E-TTL autoflash



1/1 - 1/8192*¹ ( First curtain only when the second curtain is set.)
*¹ Less than 1/128 power possible only with Speedlite EL-1, used as receiver unit(s), as of February, 2021.


*¹ Less than 1/128 power possible only with Speedlite EL-1, used as receiver unit(s), as of February, 2021.

Wireless Functions

Transmission System

Radio Transmission

Transmission Range

Approx. 98.4 ft. (30m)

Flash Ratio Control

1:8 - 1:1 - 8:1, power 1/2-stop increments

Flash Coverage

Transmission Angle: 360° all around

Second-curtain Sync

*² Cameras that support wireless second-curtain sync as of February 2021:
• EOS-1D X Mark III*³
• EOS R5*³
• EOS R6*³
• EOS M50 Mark II
*³: Camera body must have firmware installed that supports Speedlite EL-1.

Receiver Operation Confirmation:

Green Light
Lit: Radio Transmissions Okay
Red Light
Lit: Not Connected
Blinking: Transmission Error/ Too many units (Sender units + sender units = more than 15 units)
Orange Light
Lit: Sub-sender transmission
Blinking: Receiving remote release shooting, linked shooting signal

Receiver Unit SE Mode Cancellation

The test flash button can be pressed to test if the receiver units fire or cancel the auto power off status.

LCD Panel


172 x 104 dot display


Power Source

AA/LRG Alkaline Batteries x2(Ni-MH and Lithium batteries can also be used)
Battery Life: Approx. 10 hours continuously when using AA/LR6 alkaline batteries (At a room temperature 23°C/73°F).

SE Mode

Power off after 5 min. of idle operation


2.7 (W) x 2.4 (H) x 3.0 (D) in. / 67.4 (W) x 61.5 (H) x 77.4 (D) mm


3.9 oz. / 110g (excluding battery)

Speedlite Transmitter ST-E3-RT (Ver. 2)

Speedlite Transmitter ST-E3-RT (Ver. 2)
  • Speedlite Transmitter ST-E3-RT (Ver. 2)
  • Soft Case
  • Warranty Card (USA/CA)


* When used with the Speedlite EL-1 in combination with an EOS R5, EOS R6, EOS-1D X Mark III or EOS M50 Mark II camera. Some features will work with older Speedlite models such as 600EX II-RT, 600EX-RT and 430EX III-RT, and previous EOS cameras, but not all. As of February 3, 2021.

† Prices and specifications subject to change without notice. Actual prices are determined by individual dealers and may vary.

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