Back in the days of film photography, ISO referred to a film's sensitivity to light, and you were stuck in whatever ISO film you happened to have bought. With digital cameras, however, it's a synthetic effect, so adjusting ISO will alter the graininess and softness of the picture you're taking (referred to as "noise"). The higher the ISO, the more sensitive the sensor is to the light, which is good in dark places, but this can also result in unwanted noise. The lower the ISO, the less sensitive the sensor will be to light, which is better for bright places – but this will soften the edges of everything. "You should use ISO to tweak lighting: Raise it when it's dark, lower when it is light," Winter says. "A good languid morning shot, like this one in Bagan, Myanmar, worked because I constantly checked my light as we were gaining altitude in the balloon."
Credit: Steve Winter
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