hi i recently bought 420 ex flash there is two functions; ETTL and High speed sync HP.... refering to some of the articles, i understand that HP (FP) can be used in fill in flash but in other readings, it showed that ETTL Av mode can also be used....so can i know the REAL difference of these two mode? thasnk

-- luic (luicbee@hotmail.com), May 06, 2001

Answers

You don't state which Camera you have this mounted on. I'll assume one that offers E-TTL metering (Rebel G or 2000, Elan II or 7, EOS 3, EOS 1V. International designations: 500N, 300, 50, 30, 3, 1V. Can't remember any others besides the IX APS cameras).

For fill flash you can use regular E-TTL (or TTL, which the 420EX does on some camera bodies) with Av, Tv and M modes, and even P in some situations. But if the ambient light is bright, you are using a fast film or a fast aperture lens, the shutter speed may exceed the max sync speed of your camera (Rebel=1/90, Elan=1/125, EOS3=1/200, EOS1V=1/250). That's when you want to turn on the FP flash. Then you can use any shutter speed you want as long as you don't exceed the maximum flash to subject distance (which is greatly reduced in FP flash).

By the way, FP flash uses E-TTL metering as well.

-- Jim Strutz (jimstrutz@juno.com), May 06, 2001.