When your camera is set to auto or program, the camera reads the light and sets the f/stop and shutter speed for you. This is point-and-shoot at it’s best, and worst. Sometimes, the camera may fire the flash when natural light would actually look better. The camera may also choose a shutter speed that is too slow to be handheld for a clear picture, or too slow to capture the action. Now that we have the capability to change the ISO easily, we can adjust the ISO to a higher number, making the camera more sensitive to the light.
As previously stated: If there’s enough light available, with the camera set to a higher ISO, you can turn off the flash and shoot with available light. In addition, when the camera is set to Program (P) and not Auto (Green,) raising the ISO will also force the camera to use a faster shutter speed, which may be fast enough now to handhold the camera or stop the action your trying to capture.
So what’s the catch? Noise. We called it “film grain” when we shot 35mm: As the ISO number goes up, photos become more and more “grainy.” Digital noise equals tiny bits of misinformation that get in the way of the overall clarity of the photo. As the ISO is raised, our photos don’t look as sharp, crisp, or clean because of the noise. I think it’s a worthwhile trade-off when trying to shoot candid, nothing kills candid photography like a flash going off, and the artificial quality of flash photography can be unflattering at best. Using available light, which sometimes in artificial, means that we’ll have to keep a eye on our colors to make sure they look correct. More on that later when we cover adjusting your camera’s white balance.
The next installment in the series: “Green Auto is The Devil!”