Understanding Fill Flash

[jnick]

Something I am trying to "conquer" is fill flash. We all know how harsh the lighting can be when outdoors, especially mid day. In these situations, I always shoot with my 430EX, however, I don't understand how it works in regards to fill flash.

My understanding of fill flash (in this scenario) is a smaller flash emitted by the 430ex in order to light the shadowed areas that are casted by the sun. However, when in ETTL-II, does the flash/camera know to account for fill flash? When the camera is in manual mode, do I expose as I normally would? Or do I now have to either under/over expose the internal light meter in order to get the proper output?

I realize when the flash is in manual mode, it's a matter of trial and error in order to get the proper exposure/fill flash, but what about in ETTL mode?

Any help is appreciated!

[The Fox]

I set the camera to its sync speed, in your and my case it is 1/250th and adjust aperture to get a correct exposure for the background. Then set the flash to ETTL, and it will find and expose for that.

[Curtis N]

It's as much art as science, and requires practice and experience.

Keep in mind that your flash will not just lift the shadow areas but also add light to the highlight areas as well. So if you underexpose the ambient a little bit, it's easier to add fill flash without blowing out the highlight areas.

Setting FEC at zero with E-TTL normally doesn't provide enough light for complete exposure with flash as the only light source, so if you start somewhere between 0 and -2/3 for fill flash you'll usually be in the ball park. Chimp and adjust from there.

[jnick]

Thank you both for the info!

Curtis, when you say adjust the FEC, you're referring to lowering the output power of the flash THROUGH THE CAMERA by 0 to -2/3 a stop? Or are you referring to making the light meter in the camera read 0 to -2/3 stop under exposed?

Also, in this case, I should be metering off of the background with hopes that the flash will light the subject? Or do I still meter off my subject in the frame?

[luigis]

My recommendation is: Expose the background right using manual mode, when you are fine with the background just put the flash in TTL mode and it will automatically create the amount of fill light to make the foreground look good.
The key to fill flash (IMHO) is not to care about the flash but about the background.

Of course this doesn't always produce the best results to tuning might be needed but I think it is ok for more than 50% of the scenes.

Luigi

[Curtis N]

when you say adjust the FEC, you're referring to lowering the output power of the flash THROUGH THE CAMERA by 0 to -2/3 a stop?Right. Flash Exposure Compensation (FEC) can be adjusted with the camera or with some flash units including the 430EX. Take yer pick.

The meter in the viewfinder measures ambient light only, and is a helpful guide for adjusting the background ambient exposure.

I agree with the advice above to use M mode on the camera for metering the background. It's not the only way to do it, but it gives you the best control and I think will give you the most consistent results in the long run.

[Lotto]

Q for Curtis: outdoor day light, Av mode will set the ETTL flash to fill, any difference if the camera is in M mode as far as flash metering?

[Curtis N]

Q for Curtis: outdoor day light, Av mode will set the ETTL flash to fill, any difference if the camera is in M mode as far as flash metering?I have seen no evidence that E-TTL works any differently in M vs. Av or Tv. I have done a few tests (not real scientific) that seem to confirm this. I would take a shot in Av mode, check the EXIF, switch to M with the same exposure settings and take another shot, and I see no apparent difference in the flash exposure. It should be easy enough for you to do the same sort of test to see if I'm nuts (be sure to keep the same composition to minimize E-TTL variance).

So regarding the part of your quote that I have in bold, I think it's a widely held misconception.

[Lotto]

Thanks Curtis. Most of my flash shots are indoors and don't use Av mode, maybe that's where the misconception is coming from.

[jnick]

Curtis, when I meter off the background, should I be exposing for the lows, mids, or highs of the BG? I would assume that exposing off of each should give different results...?

[Curtis N]

Exposure is a matter of artistic choice. You can meter the sky and make it a nice, deep blue. Or you can meter something else.

Experiment. Try different techniques. Electrons are cheap.