Here's an easy way to use fill flash
Photographer: Chuck Vosburgh. Model: Kristy Neuenschwander. Assistant: Pat McGlinchey
Fill flash does one thing; it lightens up shadows. By using fill flash, you can control the exposure of the background and the subject separately. Below is a photo taken with the sky the way I wanted it to appear. The problem is that it leaves the subject way too dark, and if I expose the subject properly the sky will be too light. Here's where the fill flash comes in.
It's a two-step process
1: Get the background exposed the way you want it.
2: Add enough light on the subject to expose it the way you want.
But there's a catch
Most cameras can't sync with an off-camera flash at more than 1/200 of a second. That means the shutter speed must stay below the sync speed no matter what. To make that happen, you may need to adjust the aperture and/or ISO. Also remember that like everything else in photography, there are always limits to what is possible.
So, getting back to the example, the first shot is 1/60 of a second at f-8 and ISO 100. The second shot is the same, except a flash was added. The way I do it is to set the flash at 1/4 power and either use a flash meter to determine the exposure or take a test shot and then adjust from there. Remember, you already have the background set, so all that we need to do is adjust the light on the subject. There are two ways to control the light on the subject; flash power and aperture. The shutter speed controls the ambient light (background). In this case, I increased the flash power to 1/2 power and it was perfect. Increasing the aperture to f-5.6 would have produced the same result if I left the flash power at 1/4 power. Open up the aperture or increase the flash power. Both are effective ways of making the exposure of the subject lighter.
The setup is simple. One off-camera flash.
The best way to master fill flash is to get out and use it, so get out and experiment! You'll master it in no time at all.