Originally posted by pathdoc This raises two questions in my mind:
1) Do flashes have reprogrammable firmware the way digital cameras do?
2) Isn't this an issue that can be solved with a mode switch, just as is planned for DA-only vs. FF lenses?
As far as I am aware, doing TTL without a pre-burst requires only that the camera be able to issue an order to shut down the flash emitter once the appropriate amount of light has been delivered. The issue, which my first question addresses, is to what extent current P-TTL flashes are able to accept such an order as they currently stand.
Current shooters of the *ist-D who also own an AF360 or 540FGZ-II are invited to comment. Also, I haven't yet done that much shooting with my 540FGZ-II, but I could have sworn when playing with the menus the other day that I saw a TTL option offered without a P prefix.
Yes, the camera must be able to send a signal to the flash to shut down the lamp. However, the camera must have additional hardware, within the mirror box to, somehow, determine when the proper amount of light had been received, Current cameras do not have such hardware.
In the P-TTL system, the preflash is fired while the mirror is still down. The light sensing is done using the same photocells in the viewfinder that measure ambient light. The preflash goes off, the sensors read the returning light, the mirror goes up, the shutter opens, the main flash is triggered. The shutter closes, the mirror returns. While the mirror is up, the light sensors in the viewfinder do not receive any light from the lens.
It is the requirement for additional hardware that makes a return to TTL unlikely.
And, one must be careful when reading specs for flashes. I have seen several cases in which the specs referred to TTL, when the context clearly shows that the authors mean P-TTL, I-TTL or E-TTL; that is, preflash technology, not reading the light during exposure.