Not compatible with EOS digital SLR`s.

There’s also the camera-mounted TTL Hot Shoe Adapter 3, which runs off a small lithium CR-2025 battery. This adapter connects with various dramatically costly accessories - 60cm and 3 metre connecting cords, the tripod-mount-equipped Off-Camera Shoe Adapter OA-2 for connecting Speedlites to cords and a TTL distributor that lets you hook one camera up to 3 flash units.


The cords must be used in conjunction with the Hot Shoe Adapter 3 and the Camera Shoe Adapter and connect together using mini-DIN style connectors - they don’t use, say, PC connectors or anything like that. Note: there was also the original Hot Shoe Adapter (no numeric designation), which worked only with the T90 and does not work with EOS cameras, and the Hot Shoe Adapter 2, which does work with EOS cameras.


This system works with TTL only - A-TTL and E-TTL are not supported. In fact, a whole slew of flash features are not supported if you use the TTL Hot Shoe Adapter 3 cable system. You can’t use A-TTL or E-TTL, there is no preflash, second-curtain sync does not work, the DEP mode will not work, program shift won't work, automatic flash head zooming is disabled (though manual zooming works if the flash supports it), the aperture and coupling range data is not displayed on flashes with LCD panels and the AF assist light does not work. These features are all disabled because their control signals a) are all sent down one line and b) would result in contradictory instructions from multiple flash units. (though as a side note this device can be used for disabling E-TTL features if you like)


You can’t automatically adjust lighting ratios between the individual flash units in TTL multiflash mode - all flashes will fire at the same time and shut off at the same time. There are four awkward workarounds for this problem. First, you could move individual flash units closer to and further from your subject. Second, you could stick neutral density filters or diffusers on the flash heads. Third, you could use manual zoom controls, if available, to zoom the flash head since that reduces the light output on wider lens settings. And fourth, you can use manual controls, if available, to adjust light output of each unit individually. However any flash set to manual will disable TTL flash for all of the flash units. You can’t shoot a multiple flash photo with a mixture of manual flash and TTL autoflash.


The TTL Hot Shoe Adapter 3 cord system is really only useful for older (type B) bodies and compatible flashes. In fact, the cord system doesn’t work at all on E-TTL only cameras like the digital 1D, 1Ds, D30 and D60. The wireless system supported by the latest E-TTL flash units is considerably more flexible (it supports ratios on certain cameras, for example) and convenient (no wires to trip over or limit your placement of slave units).