OFF-CAMERA FLASH WITH EOS DIGITAL CAMERAS
With the increasing popularity of using battery-powered flash units off-camera, and the quirks and complexities of Canon’s flash systems and components, certain questions often arise about how to make various units work in off-camera setups. This guide is designed to cover the basics and clear up confusion.
The options for making an off-camera flash unit sync with your camera’s shutter come down to four categories: 1) A wired connection, 2) A radio remote system, 3) Optical slaves, and 4) Canon’s wireless flash system. We’ll go into each of the options in detail. The only two options that allow E-TTL flash metering are an extended Off Camera Shoe Cord 2 or the Canon wireless E-TTL system. All other systems require manually adjusted flash power or auto-thyristor (automatic) flash units.
Attached to this post is a chart in PDF format to show which flash units are compatible with each option. The chart lists some of the more popular flash units today. I can add more models to it if you provide me with detailed information. Most of the links in this post are to products at B&H Photo. I am not recommending this seller specifically, I'm just using their site as a reference.
The cheapest cord system is a PC cord. PC cords are available in various lengths and are reasonably priced. Using a PC cord with a most Canon Speedlites will require a PC cord - hotshoe adapter like this. These adapters have a threaded hole in the bottom for mounting on a lightstand or tripod. The other end of the cord plugs into your camera’s PC socket. If you have one of the Rebel series cameras (300D, 350D, 400D), you will also need a hotshoe – PC cord adapter like this, since these cameras don’t have a PC socket. Exception to the above paragraph: The 580EX II Speedlite has a female PC socket for attaching a PC cord. Connecting a 580EX II to a camera requires a PC cord with a male connector on both ends. Alternatively, the hotshoe adapter mentioned above will also work.
Another option is to use a Canon Off Camera Shoe Cord 2 (or aftermarket equivalent) and extend it to make it long enough. Extending this cord requires some basic electrical skills. Learn how to do it here, or buy an extended cord from Michael Bass Designs.
RADIO REMOTE SYSTEMS
The professional standard nowadays is the PocketWizard brand. They are extremely reliable and have more range than you’ll ever need. One pair (transmitter & receiver) will cost about $370 US. The transmitter mounts on your camera’s hotshoe. The receiver output jack is a 1/8” miniplug and you’ll need to purchase hotshoe adapters like this or thisor PC adapter cords, depending on your setup.
The Elinchrom EL-Skyport Universal Set is a relatively new system that has received good reviews. It's about half the price of PocketWizards, but there differences in battery types, distance range and other capabilities so read before you buy. You'll still need hotshoe adapters for your flash units.
On the other end of the price scale, there are two systems available from Gadget Infinity (Hong Kong). The 4-Channel system has a receiver designed to mount on a light stand with a hotshoe for use with shoe mount flash units (review). The 16-Channel system is designed for studio lights (review) but can be used with shoe mount flash units with the right adapters. There are other brands available also.
OPTICAL SLAVE SYSTEMS
An optical slave is a sensor that “sees” the light from a master flash and instantaneously closes a circuit to fire a slave flash to which it is connected. Optical slave sensors like thisattach to hotshoe flash units, are relatively inexpensive and have a threaded hole in the bottom for mounting on a lightstand or tripod. Some flash units have built-in slave sensors (see the chart). In general, optical slave setups work very well indoors but not outdoors.
Optical slaves do not work if the master flash is in E-TTL mode. The E-TTL pre-flash fires the slave prematurely. Because of this, the built-in flash on a Canon DSLR cannot be used as a master with optical slaves. The same is true of the 420EX Speedlite and other E-TTL flash units with no manual mode. Using the FEL button to fire the preflash before taking the shot can work, but it’s not a practical way to take pictures.
Be aware that most of these slave attachments do not work when connected to Canon EX series Speedlites. Optical slaves work when connected to the PC socket of the 580EX II, but not when connected to the hotshoe. Update 01/04/09: Flash Zebra has an optical slave that will work with EX Speedlites, and Michael Bass Designs is selling a line of economical adapters to make EX Speedlites work with Sonia brand optical slaves. Info here.
WIRELESS E-TTL SYSTEMS
Some Canon Speedlites can be used with their proprietary wireless E-TTL system (see the chart). Since the master unit uses light to communicate with the slaves, it doesn’t work well outdoors and sometimes requires line-of-sight between master and slave when used indoors. The system is designed to set ratios between master and slave or between groups of slaves. The ratios and output levels are adjusted from the master unit, which makes these adjustments quick and easy. This system requires a significant investment in equipment. Sigma and Metz also make flash units that are reportedly compatible with the Canon wireless E-TTL system. Reports vary as to the reliability of mixing brands.
Edit Feb. 5, 2008:
Paul Duncan has created a short video to illustrate many of these concepts, as well as other basic equipment and terminology (gear and jargon) used with off-camera lighting. I highly recommend clicking here to watch the video.
Anyone interested in off-camera flash should definitely check out the Strobist blog, as well as the Strobist group on Flickr.