Nikon Know-how

This is­sue, our ex­pert at large ex­plores why depth of field is so cru­cial, and how to use it more cre­atively

NPhoto - - Contents -

Michael Free­man takes an in-depth look at depth of field: how you can con­trol it, and how to use it more cre­atively

As ev­ery­one knows, depth of field is de­fined as the range of dis­tance in front of the cam­era in which ev­ery­thing looks

ac­cept­ably sharp. It can be deep, cov­er­ing the en­tire scene, or it can be shal­low, with only a nar­row band sharp. It’s a term that we trun­dle out as if it ex­plains ev­ery­thing there is to know about aper­ture, but ‘why’ is much more im­por­tant than ‘what’.

And the rea­son why it needs ex­pla­na­tion is that depth of field is a visual ef­fect that we have very limited ex­pe­ri­ence of with our own eyes. Healthy, ad­justed eyes sim­ply see ev­ery­thing as nor­mally sharp. If you’re short-sighted or long-sighted (as more than a third of us are) then with­out glasses you’ll have some sense of blur, but it’s un­likely to come any­where near the smooth blur in a se­lec­tive-fo­cus shot, or in almost any macro back­ground. That’s why well-man­aged blur can be so ap­peal­ing – it’s beyond our usual visual ex­pe­ri­ence.

You change the depth of field by chang­ing size of a lens’s aper­ture (see be­low). Depth of field does not change with fo­cal length, but us­ing a tele­photo to mag­nify a small part of the scene gives the im­pres­sion of shal­lower depth of field. With a wide-an­gle lens depth of field might be, say, a me­tre at f/4, so ev­ery­thing within a me­tre of your sub­ject will be ac­cept­ably sharp; with a long lens, fore­ground and back­ground are typ­i­cally over a me­tre away from your sub­ject, so will be blurred out.

At its most me­chan­i­cal, depth of field is used to keep the im­por­tant parts of a sub­ject sharp, but there are many more in­ter­est­ing ways to use it to your ad­van­tage. You can use it to di­rect the viewer’s eye, but equally, by throw­ing some things un­ex­pect­edly out of fo­cus, you can dis­rupt the viewer’s ex­pec­ta­tions. Us­ing depth of field cre­atively means play­ing with the con­trast be­tween sharp and blurred ar­eas.

Us­ing depth of field cre­atively is a great way to di­rect the viewer’s eye to pre­cisely what you want them to look at

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