The TTL system will usually do an excellent job of balancing the flash and ambient light for your exposure, but it does have the limitation of not knowing what effect you want in your image. You may want more or less flash in a particular shot. You can achieve this by using the Flash Compensation feature.
Just as with Exposure Compensation, the Flash Compensation feature allows you to dial in a change in the flash output in increments of 1/3 of a stop. You will probably use this most often to tone down the effects of your flash, especially when you are using the flash as a subtle fill light (Figures 8.10–8.12). The range of compensation goes from +1 stop down to –3 stops.
Using the Flash Compensation feature to change the flash output
- With the flash in the upright and ready position, press and hold the flash button while viewing the control panel.
- While holding down the flash button, rotate the Sub-command dial to set the amount of compensation you desire. Turning to the right reduces the flash power 1/3 of a stop with each click of the dial. Turning left increases the flash power. Release the button when you have made your selection.
- Press the shutter button halfway and then take the picture.
- Review your image to see if more or less flash compensation is required, and repeat these steps as necessary.
The Flash Compensation feature does not reset itself when the camera is turned off, so whatever compensation you have set will remain in effect until you change it. Your only clue to knowing that the flash output is changed will be the presence of the Flash Compensation symbol in the viewfinder. It will disappear when there is zero compensation set.