Originally posted by gattofix First of all thanks a lot, Ole, for the explanation...
Yes, in case the high-speed flash was weaker than the flash in normal mode, I could always open up aperture - that's quite reassuring.
But then I looked up how the GN is calculated, and found the following equation:
GN = f/stop x Flash-to-subject distance
So exposure time seems not to be part of the equation.
I guess I really need a flash with high-speed sync to be able to do what I want to do - use the flash inside at speeds between 1/250 and 1/500.
I just would have to be sure that the high-speed sync flash would be strong enough - I am not sure if the normal GN applies to the high-speed sync mode, as well.
By the way - I always bounce my flash off a wall, not sure if that would be a problem with high-speed sync mode...
Any ideas?
gattofix
The GN goes down when you exceed the flash sync speed. That's becasue the flash now strobes instead of firing just once.
So, at 1/500 (on my flash) the GN has dropped to one third.
The shutterspeed is not part of the GN = f/stop x Flash-to-subject distance equation becasue the GN varies with shutterspeed when the speed exceeds the sync speed.