key con­cept ISO (sen­si­tiv­ity) set­tings

Along with shut­ter speed and aper­ture, it con­trols ex­po­sure

NPhoto - - Special Feature -

Your main tools for ad­just­ing ex­po­sure are the length of the ex­po­sure (shut­ter speed) and the amount of light (lens aper­ture). But dig­i­tal cam­eras have in­tro­duced a third op­tion – ISO.

In­creas­ing the ISO set­ting on your Nikon is like turn­ing up the vol­ume. If the light is poor, in­creas­ing the ISO will am­plify it and make it stronger (though this does also in­crease dig­i­tal ‘noise).

Some pho­tog­ra­phers now in­clude ISO as an ex­po­sure ad­just­ment along­side shut­ter speed and lens aper­ture to pro­duce an ‘ex­po­sure tri­an­gle’, be­cause it works on the same ba­sis – you can in­crease the ISO to com­pen­sate for a smaller lens aper­ture or faster shut­ter speed. This quickly gets com­pli­cated, though. It’s sim­pler to stick to shut­ter speed and aper­ture for rou­tine ex­po­sure ad­just­ments and only in­crease the ISO if the con­di­tions are so poor than you can’t get us­able set­tings any other way.

You don’t al­ways need to in­crease the ISO at night. If you put the cam­era on a tri­pod, you can leave it set to its low­est ISO and use as long an ex­po­sure as you need.

Shut­ter speed, lens aper­ture and ISO set­tings have been clev­erly ar­ranged so that each set­ting de­liv­ers twice the ex­po­sure of the one be­fore. You can use this to bal­ance these set­tings up so that you keep the same over­all ex­po­sure even though you’ve changed one of the val­ues. For ex­am­ple, 1/1000 sec at f/4 gives the same ex­po­sure as 1/125 sec at f/11.

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