1/2500 at f/4. (I was sure that I posted that...) I was in Av mode for this image. The advantage of using manual flash at 1:1 as I understand it is that the flash is putting out full power. At 1/2500 sec. the flash needs to fire three times (with High Speed Synch). Thus, as above, flash output (and therefore its range) is drastically reduced. This technique really works well on sunny days. In dull conditions I often use the flash in ETTL at -1 or zero and shutter speeds from 1/500 to 1/1250 sec., but here I wanted a really fast shutter speed as the boat was rocking.