Hi adjfotofilmagem
I have two of the Canon 430EX III RT Speedlite Flashes. I also own two Canon 430EX II Speedlite Flashes and a number of Canon DSLRs.
The 430EX III RT DOES send the infrared AF assist beam on the 'center zone' mode on my 7D. This is only for the central 9 squares (as per the illustration in your original post). It also sends the infrared AF assist beam on the AF point expansion, but again, ONLY where the central AF points is the very centre one. (See the attachment to my post here for that mode which I am describing). When in 19 point AF auto selection mode, it does fire the infrared AF assist beam too.
The beam is a fairly small, reasonably thin vertical set of beams. This is sadly, quite limiting.
It would have been so much better if the infrared AF assist beam was transmitted on ANY AF point to - and if it was cross type too.
The older 430EX II has a better implementation of this; as the infrared AF assist beam is transmitted when any AF point is selected. However, weirdly, when the centre AF point only is selected, it only transmits a vertical beam (but better - as in, bigger and wider spread- than the 430EX III RT's beam). On all other AF points, the 430EX II transmits both vertical and horizonal beams. It is quite effective.
Finally, a note that on my 80D with the 430EX III RT flash. On the 80D, the 430EX III RT follows the same logic as on the 7D - it transmits an infrared AF assist beam only when the centre AF point is selected (or when that is the centre of the zone selection, or all / auto AF points are chosen).
I have owned 3 x 580EX II in the past too - and at certain focal lengths for certain DSLRs, the AF assist 'dots' did not align that well (the minority of cases, true... but still). However of all of my devices, I find my ST-E2 to be the best AF assist beam of them all. It is powerful, provides great coverage (a horizontal and vertical cross pattern using any AF points). The Canon ST-E2 is small and light too, which is a bonus if you just want AF assist).
Despite the infrared AF assist beam limitation, the Canon 430EX III RT is a very nice Speedlite on the whole. The central point AF is still much better than nothing. Overall, it is an easy to use flash, has a good menu system, packs decent power into a small package. Its wireless (radio and optical) capabilities are great. I particularly appreciate that the 430EX III RT can operate as either a master OR slave in radio mode! (and as a slave in optical mode). So for the price and functionality, it works well for me.
I hope the above information is helpful. 8) Kind regards,
Paul
