Exposure Basics - ISO

ISO determines the sensitivity of the camera’s sensor to the light entering the camera through the lens. The higher the number, e.g., 100, 200, etc, the more sensitive the sensor will be to the light entering the camera. The advantage of higher ISOs is that you can use slower (lower) shutter speeds and smaller apertures (higher numbers) given the same amount of available light. The disadvantage of higher settings is the potential for “noise”, which is that grainy effect in which you start to see the individual pixels.

In the old days of film cameras, when ISO was known as ASA, 400 was considered “fast”, meaning that it could be used in low-light situations. Nowadays, settings of 2000 or even higher on some cameras can be used without generating a lot of noise. (That’s one of the main reasons I splurged on my Nikon D7000.)

With lower ISO settings, you will need one or more of, greater available light, slower shutter speeds, and wider apertures, but you will get less noise. The bottom line – don’t boost the ISO unless you really need to.