Con­trol depth of field

NPhoto - - Feature -

Shut­ter speed is, of course, the cru­cial cam­era set­ting to get right when tar­get­ing sharp shots, but the aper­ture plays a sig­nif­i­cant role as well. The choice of aper­ture has a big in­flu­ence on the depth of field – or the depth of sharp­ness through the im­age. Small aper­tures, such as f/16 and f/22, in­crease the depth of field while large aper­tures – f/1.4, f/2.8, f/4 and so on – de­crease it. It might seem wise to reach for small aper­tures to boost the sharp­ness, but there are two big draw­backs. First, you’ll need to use a slower shut­ter speed or higher ISO to ex­pose the scene prop­erly, and sec­ond, the smaller the aper­ture, the more ob­vi­ous the ef­fects of dif­frac­tion be­come. Dif­frac­tion is an op­ti­cal phe­nom­e­non where light rays en­ter­ing the lens are bent out of shape by the edges of the aper­ture blades. The smaller the hole, the greater pro­por­tion of light rays strike the aper­ture blades, and the more fuzzy de­tails and edges in a pic­ture ap­pear. Stick­ing with aper­tures in the mid­dle of the range tends to give the best bal­ance of depth of field and op­ti­cal sharp­ness.

Don’t dis­miss large aper­tures ei­ther. Hav­ing a shal­low depth of field, with a sharply fo­cused sub­ject sand­wiched be­tween a blurred fore­ground and back­ground, can ac­tu­ally en­hance the im­pres­sion of sharp­ness where it counts.

Andy used a spe­cial­ist tilt-and-shift lens to give him pre­cise con­trol over the depth of field and plane of fo­cus in this im­age of sailor Giles Scott. Though most of the frame ap­pears de­fo­cused, Giles’s face is pin-sharp, draw­ing your at­ten­tion.

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