More E-TTL info from Bill

As mentioned in a previous post, Bill Grundmann has been documenting his investigation into Canons E-TTL protocol.  Bill has just released a PDF summarising what he has found so far.

I’ve yet to go over it in detail, but for those looking at doing some E-TTL investigation of their own this document is a must.

Canon E-TTL Timings

More success from Bill Grundmann in his attempt to decrypt Canons E-TTL protocol !

It appears that there is a consistent 4msec delay between when the CLK signal from the camera body drops to GND and when the actual flash is triggered.  This would give us plenty of “leeway” in our timing to sync with the shutter I would guess.

Then next part of the puzzle is to now trick the body that it has a flash in high speed sync mode attached to achieve some high sync rates.

Next week I’ll start investigating this further (already got a pretty busy weekend on the cards )

For those of you that shoot Nikon, it might be worth looking at what Bill has done so far and see if those with knowledge can do the same for the Nikon protocol.  With the knowledge of both major protocols we just might be able to have both vendors protocols talking to each other via the Strobit Triggr.

Well done Bill and keep up the great work!

Bills’ Post:

Strobit Triggr and Canons E-TTL

Seeing as I’m a canon person as far as bodies and lens goes I thought I’d look into the E-TTL protocol and how the camera body and the flash can talk to each other.

I’m not looking to completely implement the E-TTL protocol in the Strobit Triggr, (well not yet anyway), but more along the lines of fooling the camera body that I have an E-TTL capable strobe attached and thus enable high speed sync mode.  If we know what the sequence is between the camera and the flash is, then  I can play around with the timing of the Strobit Triggers.  Why do we need to do this?

  1. By not using E-TTL we are then limited to standard hotshoe only sync speeds,  so when the camera triggers the hotshoe we are at least guaranteed 1/60 – 1/250 etc rather than some higher sync speeds like 1/1000 or more.
  2. Wireless as a transmission medium has some inherent lag due to the physical properties (i.e. air) so if we can fool the camera I have a high speed strobe attached and so enable high speed sync mode, the camera triggers will still be out of sync due to this lag.  So with some knowledge of the basic E-TTL sequence and by playing around with the timing I should be able to get the Strobit Triggrs to fire early, before the actual camera fires and still be in sync with the high speed shutter.

While I’m waiting for the boards I will look at playing around with this idea, I’ve just ordered a cheap canon E-TTL flash extension cord ( so I can gain access to the hotshoe contacts easily with my logic analyser. 

Unfortunately one of my biggest stumbling blocks is that I do not own or have access to a Canon E-TTL flash, (the only non canon equipment in my kit are my strobes mix of Nikon and Vivitar), thus started some research, it just so happens that Bill Grundmann has recently started his analysis of the E-TTL protocol and making fantastic headways.  Dang he has saved me a huge amount of time!  Well done Bill!