Canon Speedlite Transmitter ST-E3-RT

The Canon Speedlite Transmitter ST-E3-RT (Ver. 2) is a radio-frequency wireless flash controller designed to fire and manage compatible Canon RT-series Speedlites without requiring line of sight, giving photographers reliable off-camera flash control for intricate multi-flash lighting setups. It mounts to the camera’s hot shoe and supports E-TTL II/E-TTL autoflash, manual flash, stroboscopic, and auto external flash metering.

The transmitter uses 2.4GHz radio-frequency, two-way wireless communication, achieving a transmission distance of up to 98.4 ft. (30m) at a full 360-degree angle, even around corners or other obstacles that would interrupt a traditional optical wireless system. A single ST-E3-RT (Ver. 2) can control up to 5 groups or 15 individual Speedlites, with 15 selectable transmission channels and radio IDs to help prevent misfiring from interference on a shared channel.

This Ver. 2 update adds wireless rear (second) curtain synchronization, letting a remotely triggered flash fire as the shutter closes to capture light trails and a sense of motion, along with a minimum flash output of 1/8192 power (supported with the Speedlite EL-1) for working in very low ambient light, and FE Memory, which locks in an E-TTL flash exposure level for consistent results across a multi-flash scene. Other supported features include High-Speed Sync, Flash Exposure Lock (FE Lock), Flash Exposure Bracketing (±3 stops in 1/3- or 1/2-stop increments), Flash Exposure Compensation (±3 stops), and modeling flash. The transmitter can also remotely trigger a compatible EOS camera or Speedlite, such as the 600EX II-RT.

Handling centers on a dot-matrix LCD panel (172 x 104 dots) displaying all relevant settings simultaneously, along with backlit controls for easy operation in low light. The unit offers 8 custom functions and 3 (or 4, depending on source) personal functions for further customization. Build quality includes weather-sealed construction against dust and moisture, matching the durability standards of Canon’s professional EOS cameras and L-series lenses, along with high-performance hot shoe contacts for reliable information transmission.

The transmitter runs on 2 AA batteries (alkaline or Ni-MH), rated for approximately 10 continuous hours of operation, and measures approximately 67.4 x 61.5 x 77.4mm, weighing approximately 110g. It ships with a soft carrying case.

Key Features
– Radio-frequency (2.4GHz) wireless Speedlite transmitter, no line of sight required
– Controls up to 5 groups or 15 individual Speedlites
– Transmission range of up to 98.4 ft. (30m), 360° angle
– 15 selectable channels with radio ID interference protection
– Wireless rear (second) curtain synchronization
– Minimum output of 1/8192 power (with compatible Speedlite EL-1)
– FE Memory
– E-TTL II/E-TTL autoflash, manual, stroboscopic, and auto external flash metering
– High-Speed Sync, FE Lock, Flash Exposure Bracketing, Flash Exposure Compensation
– Modeling flash
– Remote camera/Speedlite triggering capability
– Dot-matrix LCD panel (172 x 104 dots) with backlit controls
– 8 custom functions and 3-4 personal functions
– Weather-sealed (dust- and moisture-resistant) construction
– Runs on 2 AA batteries (~10 hours continuous operation)
– Includes soft case
– Approximate weight: 110g