What are the key things to know about ISO?

Your cam­era’s ‘sen­si­tiv­ity’ con­trol can al­low you to keep shooting when the lights dim – but it’s ac­tu­ally much more ver­sa­tile than you might think…

Digital Camera World - - CAMERA COLLEGE -

There are three key cam­era con­trols that de­ter­mine the ex­po­sure of a pic­ture: aper­ture, shut­ter speed and ISO. The size of the aper­ture (the hole in the lens) dic­tates how much light enters the cam­era, with the shut­ter speed reg­u­lat­ing how long the imag­ing sen­sor is ex­posed to that light. But it’s the ISO that de­ter­mines how much light is re­quired to make an ex­po­sure.

ISO es­sen­tially con­trols the sen­sor’s sen­si­tiv­ity to light. I say ‘es­sen­tially’ be­cause tech­ni­cally it doesn’t re­ally make the sen­sor more or less sen­si­tive: the light fall­ing on it is con­verted into an elec­tri­cal sig­nal, and the ISO set­ting de­ter­mines the de­gree to which this sig­nal is am­pli­fied.

The cam­era will set an ap­pro­pri­ate sen­si­tiv­ity when you’re us­ing an au­to­matic shooting mode, but once you move to more ad­vanced modes such as Aper­ture Pri­or­ity and Man­ual, you can opt to con­tinue us­ing Auto ISO or set the sen­si­tiv­ity your­self. Dig­i­tal cam­eras typ­i­cally have an ISO range of 100 to 6,400, with lower num­bers mak­ing the sen­sor less sen­si­tive and higher num­bers in­creas­ing the sen­si­tiv­ity. The more sen­si­tive a sen­sor is to light, the less of it you need in or­der to record an im­age, so you can carry on tak­ing pictures when there’s not much of it avail­able.

As a rule, you should keep the ISO as low as

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