Disneyboy,
thanks for the great info. I was wondering about the compensation settings. Looks like I'll need to do some more experimenting with different FEC's to get a better understanding of it.
BTW, that is an awesome shot of the parade. About what kind of range can you expect when using fill-in-flash? I know I used it when I was only a few feet from my daughter. Would the fill flash have about the same range as the normal flash? Do you need to learn to adjust your FEC as the range increases, or is there perhaps a good rule of thumb that helps you know how to adjust the FEC as the range increases / decreases? Or is it more situation (brightness, composition, etc...) that determines FEC rather than just distance (or maybe a combo of different things).
Again, thanks for the info, and I look forward to trying to put it to good use.
There are others who know tons more about flash than me, so hopefully others can chime in.
Whether you're using your flash for fill or not, if you decrease your flash exposure compensation (FEC), then you flash will give out less power than if your FEC were at zero.
There are several things that affect the exposure from your flash: (1) the distance to your subject, (2) the aperture you've set, (3) the ISO you've chosen, and (4) flash power. FEC is a way of controlling the flash power. You can also control the flash power manually.
One other thing about flash distance you're probably already aware. Your subject probably shouldn't be too far away from your flash. There's a concept called
inverse-square law that you might remember from physics but is very applicable to flash photography. If your subject moves further and further away from the flash, s/he'll receive substantially (exponentially) less and less light from the flash.
In nerdy terms, if the flash-to-subject distance doubles, then the subject receives only 1/4 of the light from flash (or, you'll need 4x power from your flash to get the same illumination on your subject). If the flash-to-subject distance triples, then the subject receives only 1/9 of the light from flash (or, you'll need 9x power from your flash to get the same illumination on your distant subject).
In fact, before our flashes had "TTL", photographers had to manually calculate the flash power & flash exposure based on (1) distance, (2) aperture, (3) ISO/film speed. Nowadays, we've got TTL with our flashes, so we let the flash & camera do all these calculations to automatically determine the correct flash exposure.
TTL stands for "through the lens", which means that your flash first fires a pre-flash to determine how much power the flash really needs for your photo. Based on how much the subject is lit by the pre-flash (as seen by the camera "through the lens"), the camera will then control how much power to fire the flash so that you get a proper flash exposure. Think of TTL as an "auto" mode for your flash.
In the end, you can basically set your flash to TTL, and just let the camera worry about the flash exposure. Just set it and forget it! So no need to worry about the distance to your subject or any other camera settings. Occasionally, you can adjust the power of the flash by adjusting the FEC, but that's basically all you have to do.
I stumbled on the power of TTL at Epcot one night when I was trying to learn more about using my external flash. No matter what crazy camera settings I had in Manual mode, I always ended up with a proper flash exposure.