It doesn't. TTL flash controls flash exposure by varying the *duration* of the flash, not the power. So... During TTL flash exposure with -1.5 stop compensation, the system will shut off the flash (this happens in milliseconds) when the amount of exposure has reached 1.5 stops less
than the meter deems necessary. The *shutter*, however, will remain open for the necessary amount of time for proper, uncompensated, exposure.
So what you have is a combination of ambient exposure at standard and flash exposure at -1.5 stops.
Mark, this is probably the bit of knowledge that I did not have. My (wrong) understand was that by issuing exposure compensation at, say -1.5 stops, I actually let 2^1.5 less light strike the film. So in a sense I thought that even when using the flash one still thinks in terms of integrated exposure, so to say.
Well, I think I am proven wrong by your explanation and by my lack of successful photos while using the flash - both built-in in ZX-L and with AF220T that I had on loan...
Wisdom of PDML is indeed infinite <grin>.
Boris
