FEC and EC interaction

mercphoto

I'm trying to determine how FEC and EC interact with each other with respect to the baseline exposure. For example, if I dial in -2/3 FEC and take a picture, the flash will fire with a certain amount of power. If I then dial in some positive EC, does that increase the flash power or not? Is the FEC value biased off the standard exposure reading or off the EC value dialed in?

If it matters, I'm shooting Canon.

Also any way to tell how strong the flash fired on any given shot? Would be useful info to have when learning.

BenA2

In Av, Tv, and M modes, the EC has no impact on flash power at all. In P mode, however, I've wondered exactly the same thing and hope someone out there has the answer. Oh, and I'm also not sure about Av mode when you use the custom function to lock shutter speed at max flash sync speed.

I've meant to test this myself. It should be fairly easy. But, I haven't gotten around to it.

Richard

Bill,

Everything you ever wanted to know about Canon flash can be found here.

Cheers,

BenA2

rsinmadrid wrote:

Everything you ever wanted to know about Canon flash can be found here.

Well... not everything. I've learned nearly everything I know about Canon flash phtography from that very website. But, I cannot find anything that conclusively answers Bill's question. The closest I come is this:

Program (P) Mode flash wrote:

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]On most if not all EOS cameras, P mode is not shiftable when flash (internal or shoe-mounted Speedlite) is used.[/SIZE][/FONT]

If "shiftable" is refering to setting +/- EC, than what I've said in my first post is true. EC has no effect on flash power in any mode on "most if not all EOS cameras". Even if this is the case, which EOS cameras are the exception?

I'm still looking for something more definitive.

Richard

BenA2 wrote:

I'm still looking for something more definitive.

This is from part 3:

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1] FEC is adjustable in half or one-third stop intervals, depending on the camera and flash. You can apply both positive (more light from the flash) or negative (less) compensation, usually by up to three stops. Remember that, on cameras which have it, FEC is completely independent from regular exposure compensation on your camera. (cameras which lack FEC simply adjust flash and ambient compensation simultaneously) It’s quite possible to, for instance, apply plus 1 stop FEC and dial in minus two stops exposure compensation at the same time. Just like regular light metering, one stop represents a doubling or halving of light output. Altering FEC means altering power output, not distance. (see the section on guide numbers for more information) [/SIZE][/FONT]

[FONT=Verdana, Arial, Helvetica, sans-serif][SIZE=-1]It sounds to me like your first post is correct.
[/SIZE][/FONT]