Built in flash techniques: 02. Use flash exposure compensation
Flash exposure can be varied just like the overall exposure, however, instead of using the exposure compensation control you need to use the Flash Exposure (FE) compensation control.
This will increase or decrease the flash output depending upon what you dial in.
It’s worth noting that with modern TTL (through the lens) metering systems the exposure is adjusted above and below what the camera considers to be correct.
Flash exposure compensation is a very useful feature that helps to balance flash power with the ambient light, which means it’s great when you’re using fill-in flash mode.
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