Will that also work with the 420EX
I think so ... but of course as I should have said in my statement about the 550EX
Choose any combo you like within the power range
of the flash. Setting f22 for a subject 50 meters away ain't gonna work, as the flash doesn't have that much power.
The 420EX is less powerful, and hence more restrictive, but you should still be able to say set f4 in manual or AV
mode and the flash takes care of the rest. Actually AV
mode is very much like manual mode in "normal" flash photography, as the shutter speed is fairly irrelevant. When using fill flash or long exposures, the shutter speed does matter, and manual will offer more control than AV
Colin K. Work, Pixstel