For sophisticated lighting setups

If you're an advanced enthusiast or professional whose flash photography has progressed to coordinating synchronized groups of Canon flash units for complex lighting, then the ST-E3-RT Speedlite Transmitter is made for you. Using radio frequencies, the ST-E3-RT offers extensive metering options, multiple flash modes, and two-way communication over a range of 98.4 feet. It controls up to five groups, or up to 15 individual Speedlite flashes.

Compact and rugged, the ST-E3-RT features a detailed, logically laid-out back-lit information panel, so you'll have up-to-the-instant feedback right at your fingertips. Note: because the ST-E3-RT only communicates by radio frequency, it is not compatible with older Canon Speedlite models that only communicate via optical transmission, like the 580EX II.

Product Highlights:

  • 2-way radio frequency transmitter for sophisticated control of multiple-flash setups
  • compatible with Canon EOS cameras that support E-TTL or II/E-TTL autoflash
    • does not support optical transmission. Not compatible with older Speedlite models like the 580EX II.
  • supports high-speed sync (for Canon EOS 1D X or 5D Mark III only)
  • radio transmission range: 98.4 feet
  • transmission angle coverage: 360°
  • uses two "AA" alkaline, Ni-MH, or Lithium batteries
  • powers off after 5 minutes of idle operation
  • 2-11/16"W x 2-3/16"H x 3-1/4"D
  • 3.9 ounces
  • warranty: 1 year
  • Our 60-day money-back guarantee

Hands-on research

What's in the box?

Download owner's manual

  • ST-E3-RT Speedlite transmitter
  • Soft case
  • Instruction Manual
  • Regions of Use and Restrictions
  • Warranty Card

Product Research


Overview: The Canon ST-E3-RT is a camera-mounted transmitter for wirelessly controlling multiple Canon Speedlite flash units. The transmitter uses 2-way radio waves to communicate between the master and slave units. It can control up to 5 groups, or up to 15 individual flash units. It can be mounted to Canon EOS digital cameras with a hot shoe. Some restrictions exist with cameras released before 2012.

Range: The ST-E3-RT operates on 2.4 GHz radio frequencies which provides 360° of coverage with a range of up to 30 meters (98.4 feet). Using radio waves, the unit does not have the same directional limitations of traditional optical wireless transmitters, such as physical obstacles.

Compatibility: The ST-E3-RT is compatible with Canon Speedlites with the Radio Transmission Wireless Function, such as the 600EX-RT. It does not have an optical transmission function, so it is not compatible with some earlier Speedlite models, such as the 430EX II or 580EX II.

Wireless Flash Shooting: Using a transmitter and a compatible Canon Speedlite, you can shoot with advanced wireless multiple flash lighting in the same way as using normal E-TTL II/E-TTL autoflash shooting. If desired, you can also shoot in the Manual Flash mode. The settings of the transmitter attached to the camera (master) are automatically transferred to the wirelessly controlled Speedlite (slave). You can use one slave unit, or divide the slave units into two or three groups, and perform E-TTL II/E-TTL autoflash shooting. You can also set and shoot with a different flash mode for each firing group, up to five groups.

Stroboscopic Flash: Stroboscopic flash is an advanced manual flash shooting method with multiple flashes in rapid succession for a single photo. Using stroboscopic flash with a slow shutter speed lets you capture successive movements within a single picture, similar to stop-motion pictures. You can set the number of flashes (up to 100) and the flash frequency (up to 500 Hz) in the menu. You will also need to calculate the shutter speed (Number of flashes ÷ Flash frequency) to make sure the shutter stays open until the end of the continuous flashes.

Modeling Flash: When the camera's depth-of-field preview button is pressed, the flash fires continuously for 1 second. This "modeling flash" lets you see the shadow effects of the flash on the subject and the lighting balance.

FEB: The ST-E3-RT's Flash Exposure Bracketing (FEB) function allows you to take three shots while automatically changing the flash output. The range can be set to up to +/-3 stops in 1/3-stop increments.

Linked Shooting: Linked shooting is a function that automatically releases the shutter of a slave unit camera by linking it to a master unit camera. You can shoot with linked shooting for up to 16 units, including both master and slave units. This allows you to shoot a subject from multiple angles at the same time.

LCD: The ST-E3-RT features a 1-7/8" (W) x 1-3/16" (H) LCD screen that displays the flash transmitter's settings and status.

Transmission Channels: To avoid interference with wireless multiple flash systems using radio transmission used by other photographers, you can change the transmission channel (1 to 15 or Auto) and wireless radio ID (4-digit number: 0000 to 9999). You should set the same channel and ID for both the master unit and the slave unit.

Memory Function: You can save the wireless settings and recall them for later use.

Power Requirements: The ST-E3-RT operates on two AA alkaline batteries (not included). Fully charged batteries provide approximately 10 hours of wireless flash shooting time. The unit will power off after 5 minutes of inactivity to save battery power.

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Canon ST-E3-RT Speedlite Transmitter Reviews

Average Customer Review:

2 reviews
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Hit or miss

Written By Starphotog, Alabama on Wednesday, January 01, 2014

Crutchfield Customer Review (What's this?)

This is a hit or miss item! By that I mean sometimes it works perfectly sometimes it doesn't work at all. Every assignment is a crap shoot. It works great then it doesn't work at all even with the camera an inch from the flash! I'll say when it does work it works great but maybe it's a 60/40 work/doesn't work thing.

Pros: Quality build

Cons: Doesn't work ever shot

Canon ST-E3-RT

Written By Randy S, Crimora, Va on Wednesday, November 27, 2013

Canon hit it on the nail head this time with an easy to use radio controller for multiple groups of speedlites. Easy to use even for a beginner in off camera flash photography.

Pros: Nice that it uses AA batteries and not some expensive odd ball ones.