basic flash questions...

So I have read a the abridged EOS bible here, the manual for my flash, and a good portion of the real thing, and I feel like I'm still missing quite a few things. I apologize if all these questions have been answered 100 times before but I have spent a good deal of the past couple days trying to figure out how this thing works.

So I have a 430 ex II that im using as a slave with my 7D built-in flash as a master.

Does ETTL metering automatically do everything for me as far as the flash strength go, even if its a slave?
What do I need to physically set on the flash?
I hear that different camera modes effect flash differently. I virtually always use M, and just watch my meter while i adjust things. I assume this does not work because the camera is metering without the flash, correct? what should I do differently?
How is the metering different if I use diffusion? Do i need to change anything on the flash, like set exposure compensation higher to compensate for the loss of light?

Indoors always shoot with your camera in "Manual Mode" when the external flash is attached. For starters simply set your camera parameters at f5.6, 1\100, ISO400, and your external flash to ETTL Evaluative mode. Take a test shot and then you can adjust the FEC + or - to your tastes on your foreground subject. The in camera settings above is a starting point for the background ambient lighting which you can also re-adjust dependent on the existing ambient light. The FEC + or - is simply exposing the right amount of light on your foreground subject.

Here is a link to read that should help:

http://photonotes.org …les/eos-flash/index2.html

Personally when i shoot outdoors in late afternoon light i always use AV mode, which with the external flash attached creates fill flash.

Regards,

slash17 wrote in post #11998137
So I have a 430 ex II that im using as a slave with my 7D built-in flash as a master. Does ETTL metering automatically do everything for me as far as the flash strength go, even if its a slave? What do I need to physically set on the flash?

Well, it does what E-TTL does, which may or may not be acceptable to you. All you need to do is turn the flash on in E-TTL mode and make sure it's set to work as a slave. If the flash is on, it will always fire but might do so at very low power. In M or Av, you can compose a shot, metered 'right' and you will still get flash! BTW, remember that you can set your pop-up flash to either fire as a flash or only fire the preflash command.

In M, the metering just meters so I would say it is working. But it's only metering ambient; it's not calculating any kind of flash for you. It doesn't care about the flash. If you have the flash turned on with the meter centered, I think (but I don't know for a fact) that the flash will fire at minimum power because there isn't much extra illumination needed. The more you underexpose on the meter, the more the flash will add to bring the exposure up to a 'correct' level.

E-TTL theoretically compensates for diffusers but I think you will find that with larger ones that absorb more light (softboxes and so forth) you'll be getting into manual flash to get the results you want.

I have been having a similar problem and these two great answers have made things much clearer. Thanks, guys!

AntonLargiader wrote in post #12000328
E-TTL theoretically compensates for diffusers but I think you will find that with larger ones that absorb more light (softboxes and so forth) you'll be getting into manual flash to get the results you want.

PaceAce and I recently conducted flash tests of Canon 580EX and Metz 54MZ with a small softbox (5" x 7" Wescott Micro Apollo) on a variety of camera models with a variety of lenses. We find that ETTL might expose well with bare flash or bounce flash, but when the small softbox is added (and flash is pointing forward with head in usual position), ETTL for some reason either UNDERexposes or OVERexposes! We are uncertain as to the root cause of this, and what determinant causes one vs the other exposure error. The result does not vary with camera model, but does apparently vary with lens choice. Additional testing might determine why this is.

Interesting. I don't have nearly that amount of experience but from trying remote flash in different ways I find that I get inconsistent E-TTL results once I get too far from a standard flash scenario. It could be some sort of a scaling problem; that the required flash is just too much more than can be indicated by the preflash. I thought I'd only had underexposed shots, but now I'm not so sure.