Because even the best machines are imperfect, there are usually methods for making manual adjustments to their work. This is the case where exposure values (E/V) are concerned. This comes into action because a camera might not always be able to make the proper assessment of a scene or particular photographic demand.
What does that mean? Well, consider a snowy landscape; it is full of bright whiteness all around, but many cameras would record this as a somewhat gray image. This would be due to the sensor deciding on its own that the very bright part of the image is actually a mid-point instead. This turns white snow to grey and makes any darker areas of the scene even more so.
This is the time to utilize the E/V compensation setting of your camera to demand that the exposure is bumped up or down accordingly. The rule of thumb is that brighter scenes nudge the E/V value up one or two digits and darker scenes take it down a bit as well.
So, you have the exposure of the scene under control, why would you need to use the flash unit? Well, let’s leave the snowy setting behind and head to the beach. Out on the bright golden sands, the sun does very much the same thing to the camera as it does in the snow. It allows it to see the brightest part of the sands as the mid-point, which makes other things very dark. It also causes some photographs to end up as under exposed images. This occurs because the sensor takes all of that brightness and forces the camera to use a faster shutter speed and smaller aperture in order to avoid an over-exposure.
If we have already learned the lesson about E/V in a snow scene, we can then do the same exact thing for a beach scene, BUT we are going to use the flash for our pictures. Why? For this image we are photographing a group of friends gathered together with the brilliant and sunny beach in the background, and we need to ensure that there are no areas of darkness and shadow. This is something known as “flash fill” and it is often a surprising technique employed by photographers snapping pictures in brilliantly lit surroundings.
Finally, many photographers do what is known as “bracketing” when using the E/V and flash fill technique. This simply requires them to adjust the E/V compensation setting up or down one digit in each direction to see which settings make the best photograph.