So the P1 has “one” radio channel, but my ETTL flashes have 4 channels.  How do these mix?

Elv posted a comment the other day asking this basic question:
“Hi, can you tell us if using the P1 with a number of other photographers using P1’s close by, could the 4 IR channels built into the Canon/Nikon sytstem be used to stop interference between users as it normaly would just using the IR, even though they’re now on the same single radio channel?”

Answer:

There can only be one active P1 transmitter in any immediate area regardless of what ETTL channel you have the slaves set to.

When a P1 Transmitter is active, it is constantly broadcasting a radio carrier signal.  The receiver units lock onto this signal and watch it for indicators that the master flash is activating.  For this reason, if another P1 Transmitter is activated in the immediate area (even if that person is using a different ETTL channel), then both P1 systems will perform intermittently as the receivers attempt to lock competing source signals.

However – in our testing we’ve found that the receivers are usually pretty good at reliably locking onto the strongest signal.  Which means if there is a bit of distance between yourself and the other shooting location your system should perform reliably.

In actual use, we expect it will be quite rare that you’ll have to “compete” for a radio signal anyway.  Except in large groups of photographers or at major press events, you’re likely to be the only photographer present with a P1 system.

You may “share” slave flashes with another photographer (like your assistant) in two different ways….

1) – Install the RadioPopper P1 Receiver without the Velcro shade installed so it can still “see” the optical line of sight signal.  If you and your assistant are both on the same ETTL channel (assuming you’re using a P1 Transmitter on your camera and your assistant is using the normal “line of sight” method) – then you can each trigger the same set of slaves as always.  You will likely trigger them more reliably as you will have the benefit of the extended range of radio.

2) – You may each use a P1 Transmitter on your master flash units.  We have designed a convenient function into the P1 Transmitter that allows you to easily “hand over” the radio signal to a second shooter.  You press the LINK button on your transmitter and the radio will stop transmitting.  It’s still powered up and ready, but it’s no longer emitting a radio signal.  Your assistant may then press the LINK button on their own P1 Transmitter and they will then take over control of the slave flashes.

A Reason for it All:

We gave much consideration to the very specific design of the radio system in this product.  The optical signals used in ETTL / iTTL happen extremely fast, with no warning, and they do not repeat.  This has lead many to believe a radio based ETTL solution was simply impossible.

The momentary sending of a signal just isn’t possible in this application. By the time a radio transmitter “spins up” and starts sending a signal, the visual ETTL system would have already completed it’s entire “conversation”.  It was therefore a requirement that the radio transmitter and receiver already establish a continual link prior to the user pressing the shutter.

We are projecting the release of a P8 model in the next several months which will perform exactly as the P1 unit, but will offer 8 different user-selectable frequencies which will allow up to 8 photographers to operate separate systems in the same location.  We expect this to be in large demand in the press and sports world.  We’ll keep you updated as that project moves forward.