EX POSURE 101 Ex­plain­ing some key con­cepts of this dark art

Digital Camera World - - DIAL M FOR MANUAL -

Re­flected light

To cal­cu­late an ex­po­sure value for a scene, dig­i­tal cam­eras use a built-in light me­ter to mea­sure the light be­ing re­flected from the sub­ject. These me­ters are cal­i­brated to 18% grey, which cor­re­sponds with the amount of light re­flected by an ‘av­er­age’ scene.

18% grey (mid­tone)

This value cor­re­sponds to a mid­tone colour half­way be­tween white and black. When a cam­era strug­gles to pro­vide the cor­rect ex­po­sure value for scenes that in­clude ex­tremes of white and black, an 18% grey card can be used to take a light read­ing from.

Ex­po­sure his­togram

The his­togram shows the range of tones con­tained in a dig­i­tal im­age. The X-axis rep­re­sents 256 pix­els, and the in­ten­sity of those pix­els is dis­played in the height of the col­umns. For more on his­tograms, and how best to use them, see Cam­era Col­lege (p58).

The his­togram can be dis­played in a mir­ror­less cam­era’s elec­tronic viewfinder, or on a DSLR ’s rear screen, with the im­age pre­view.

A range of 18% grey ac­ces­sories is avail­able, in­clud­ing re­flec­tors and lens cloths. As an al­ter­na­tive, grass re­flects the same value.

Built-in me­ters are con­ve­nient, but in­ci­dent light (taken at the sub­ject us­ing a hand-held me­ter) gives more faith­ful read­ings.

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