Flash shooting distance range (in TTL auto flash mode): 0.6m ti 20m (2 to 65.6 ft.) (varies depending on the ISO sensitivity, zoom-head position and lens aperture in use)
How do i calculate this, i will be doing an outdoor photoshoot with my 80-200 2.8 ED D and want to know how far it will reach at aperture 2.8
Thanks!
~William