EOS 3, 550EX, 70-200 f/2.8L

I've wondered about this for a while now. When shooting outdoor in near or full sun, is it to my advantage to use a smaller aperture that brings the shutter speed down to or below max sync speed and let my 550EX toss out some power? Or do I use FP mode and try to keep the shutter speed under 1/2000th? I mainly shoot with a 70-200 f/2.8L and the DOF is tight even at f/8 when racked out to 200mm. Even 100mm.

Can the powerful flash overcome the distance issue better than the problem of losing flash range when applying FP mode? The range in FP mode is dismal. 4.9 meters at 100 ISO with 1/8000th. Every stop slower adds about 2 meters of range. I use 250 ISO so I get an extra stop anyway.

-- Colin Miller (miller.photos@att.net), December 06, 2001

Answers

Your flash range at 1/8000 @ f2.8 should be about the same as 1/2000 @ f5.6 using FP mode. As you increase the shutter speed, in FP mode, the guide # goes down, but range stays the same because the aperture is decreased.

Check out the FP guide # for the 380EX at: "http://bobatkins.com/photography/eosfaq/380ex2.htm" If you run the calculation, the distance stays same for any shutter speed/aperture combinations (at the same EV), once you are in FP mode.

At 1/200 @ f16, your flash range should increase by about 30% from FP mode. I find it an advantage to shoot at 1/500 to 1/1000 with a 200mm lens (and give up some flash range), rather than try to hand hold at 1/200. For daylight fill, once you exceed normal sync speed, the FP penalty is paid and you might as well choose the best settings for the shot.

-- Kenneth Katz (socks@bestweb.net), December 06, 2001.