I never shoot indoor events so I have never needed to use my 580EX, but tonight I have to shoot a indoor event and I'm not sure on the best way to use my 580EX. I read the manual for the flash but I'm still iffy. I will be shooting with a 1d mark II and a 580EX. I just need to take head shots of people so I want to pretty much use the same setting all night long. What are the easiest way to use the flash. Thanks for the help
Keep it in ETTL with the camera in M. Indoors you'll probably want to be around ISO 800, 1/40th (unless there's motion, letting in lots of ambient looks great), f/2.8. Make one of Chuck's flash diffusers even if you're not gonna bounce.
f/4 is fine, you might just have to drop your shutter speed a little. IS will definitely come in handy. My favorite event combo is a 5D+70-200 2.8L IS for that reason.
With the camera in M mode shutter speed and ISO speed controls how bright or dark the ambient background is. With the flash in ETTL mode the FEC (Flash exposure compensation) controls foreground exposure.
Pick a shutter speed you can easily hand hold at all focal lengths, f/stop which provides sufficient DOF, and then adjust ISO to get the desired amount of background ambience in your flash shots. But be aware that too much ambience will start to create mixed color balance problems on skin tones which are almost impossible to fix. Usually I prefer to keep the background darker that "normal" (i.e. as seen by eye in person) for that reason and because it causes the background to distract less from the more important stuff in the flash-lit foreground.
The flash part of the exposure is controlled by the camera by measuring the pre-flash reflected from the scene. The pre-flash goes off after you fully press the shutter button. The camera can only guess based on the relative intensities over the 35 metering zones what is most important. Closer objects reflect more light and the camera metering assumes you know that they are most important. Because of that its critical to compose all flash shots so what you want correctly exposed is CLOSEST TO THE FLASH. Also everything you want correctly exposed must be the SAME DISTANCE TO THE FLASH. Keep that in mind when composing shots and keep all unimportant stuff out the foreground when using direct flash.
What the camera metering does is guess on how much flash power is needed to correctly expose the foreground. That guess is seldom perfect. That's were FEC or Flash Exposure Compensation comes. FEC overrides the camera's initial guess. So if you take your first shot at FEC = 0 and find the foreground subjects are either overexposed and clipping in the highlights or too dark, you'd need to dial in minus or plus FEC, respectively.
FEC can be dialed in two ways on your camera: 1) by pressing the FEC button on the camera and turning a thumbwheel, or 2) turning the wheel on the flash. I find its easier to keep track of FEC by setting it on the flash because the amount is shown on the LCD display at all times. On the camera the amount of FEC only shows when the FEC button is presses.
Because clothing causes scene reflectance to vary its necessary to "chimp" and constantly adjust FEC to maintain correct exposure on the faces. The simplest way to see when exposure is optimal is via the over-exposure warning. If you see white shirts, etc. clipping back off FEC to 1/3 stop below the point they clip. If the last shot looks underexposed per the playback or histogram an nothing in it is clipping per the OEW then raise FEC until important white highlight detail barely clips and then back off 1/3 stop.
So once you dial in the background ambience via the shutter and ISO speed you will control exposure completely with chimping and FEC tweeking. Its pretty simple actually
If you bounce the flash or use my diffuser design you'll find much more FEC is needed vs direct flash. Unfortunately in ETTL mode the flash does not indicate how much of its power was used so you find there are situations where dialing in +FEC doesn't change the exposure. That occurs when the flash is already working at or near full power. For example for + 1-stop FEC to actually increase exposure by 1-stop the flash would need to have used only 1/2 of its power or less on the previous shot. If you dial in +FEC and no change occurs to correct underexposure you'd need to raise the ISO speed or open the aperture more to obtain correct exposure.
In situations where you suspect you are at the limits of the flash range the simplest way to find out is to press the mode button of the flash to "M" mode and make a test shot at 1/1 power. Its a simple but effective way to mentally benchmark what your maximum working range will be for whatever ISO, aperture, diffusion strategy being used and I'll often do it at the start of a shooting session to get my bearings, especially if bouncing light off the ceiling. If I find things are correctly exposed at full power at 20ft. then I'll know not to exceed that distance when shooting.
