Chapter 5: Dave's rules when it comes to controlling flash

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Actually they were Canon secrets until now. What Canon is less than helpful when explaining how their flash system works with the camera body is:

E-TTL Flash uses zones to meter exposure and the camera tracks your focus point to meter ambient exposure at the same time:

  • When you are in Av or Tv program mode and you are using evaluative metering.

E-TTL Flash Exposure defaults to metering at the center of your viewfinder:

  • When evaluative metering is not set prior to doing a flash shot.

  • Any time you switch out of any one of the several program modes your camera has.

  • Any time you use FEL, regardless of if you are in program mode or not.

All learned from doing my own testing with my Canon camera. And you can do the same too. By the way the E in E-TTL stands for evaluative!

In program mode and using evaluative metering; if you off center your subject don’t center focus and recompose your image to take the shot. Rather move your focus point to where your main subject is off center and focus and shoot. 

The Canon flash system allows you to do fill flash, but it does not calculate it for the correct exposure

 To make things more confusing; in program mode it automatically reduces the exposure by one stop (it assumes you want to match flash to ambient and not reduce the flash). When set to manual mode it does not reduce ambient. So you end up having to be your own computer when figuring out the exposure. I’ve put some guide settings that work well for me (See next chapter). Try them and see if they work for you. You may have to tweak them but you should be in the ballpark when needing to get a good exposure.

As your own rule (when doing fill flash) you should meter from a standard reference point for consistency. For me when there are shadows on the face that I want to lighten up slightly, I meter from the highlight side of the face each time. Remember the flash metering area is no bigger than the small center circle area in the camera’s viewfinder. So I make sure my metering spot is fully covering the highlight side. As if it crosses over into the shadow area of the face, even slightly, it will add too much flash. Now the fill flash turns into full flash and that is not good!