A recent conversation lead me to revisit the delays between camera and wireless activated speedlights.
Andy Gock did a blog on measuring flash durations a while back and I had my replicator set up still kicking around the test bench. A bit of digging, two RF603II modules, a Yongnuo YN560IV wireless speedlight, a bit of arduino code and the unit could now be used to measure delays. Luckily I have access to all this and the Agilent Oscilloscope to measure all the ins and outs.
The basic setup diagram.
I push the big red button, the arduino spits out a 5ms(1/200) shutter emulation pulse. This is not the length of pulse a camera would send but I thought it would be nice to give some real numbers that equate to something useful like the length of time the shutter would be open on a typical flash shot. I’ve dismissed the irrelevant RF propagation delay( time it takes the RF signal to get from one unit to another) which in comparison is negligible over the short 100m distances. If we were trying to trigger one on the moon then maybe I might revisit the equations 🙂
The pulse triggers the RF603II transmitter via the hot shoe interface(a piece of veroboard gaffered to the 603, Outer casing metal is ground and the middle pin(for Nikon is the input.). Below you can see the wires and hookups. The thin black tube in front of the flash is the photodiode pickup.
The transmitter does its thing of transmitting the RF channel info. For all intents and purposes this is where half the delay actually exists. It has to transmit information serially (a string of 1s n 0s). This string is picked up by the speedlight receiver and the second RF603 unit and decoded back to a trigger pulse(the second half of the delay).
I have my Oscilloscope hooked up to various points along the way. Triggering (Blue) from the arduino output. Yellow the inverted signal fed to the TRX(just to prove no delay in my interfacing). Green shows us the actually measured light output of the flash from a photodiode(I said this was a real world test. Set to 1/64 for those curious). While finally Red, is the trigger output from the second RF unit.
So here are our results. AS you can see by the trace we have a ~580us delay from the input (yellow) to the flash(green) pickup. I tested this a few times and there was some variance in the delay. On average it was around 560us with a few at 490us and this one the longest at 580us.
Our zoomed in view of another test shows a bit more of the story. Red(the second rf503 output leads the green(flash) by about 30us. Again this was fairly consistent. I put this delay down to the YN560IV internals actually collapsing the capacitor into the tube etc.
Pretty good really, 560us to encode and then decode the trigger is pretty good and puts the light output well and truly in the first 1/5th of our shutter window of 1/200th.