Con­trol sharp­ness

A kit lens might not be ‘fast’, but you can still achieve a shal­low depth of field

NPhoto - - Feature -

Kit lenses are lim­ited by their max­i­mum (largest) aper­ture. The 18-55mm f/3.5-5.6 that typ­i­cally comes bun­dled with the D3400 has a vari­able max­i­mum aper­ture – f/3.5 at the wide, 18mm end of the zoom and f/5.6 when it’s at 55mm. Com­pare this with the max­i­mum aper­ture of two clas­sic kit lens up­grades: a ‘nifty fifty’ 50mm f/1.8, and an 85mm f/1.8. At 55mm, the kit zoom is more than three stops ‘slower’. This doesn’t mean it takes three times longer to fo­cus, but when the kit lens is used at its max­i­mum aper­ture, the smaller open­ing lets in less light, and con­se­quently a much slower shut­ter speed is re­quired for a cor­rect ex­po­sure. Slower shut­ter speeds can lead to blurred im­ages, whether that’s be­cause the sub­ject moved dur­ing the ex­po­sure or the cam­era did.

There are ways to get around this light loss (as you’ll see over the page), but there’s an­other side ef­fect of the smaller max­i­mum aper­ture: it’s much harder to blur out back­grounds. Depth of field is a mea­sure of how much front-to-back sharp­ness an im­age ap­pears to have, and it varies ac­cord­ing to the type of cam­era used, the fo­cus dis­tance and – cru­cially – the size of the aper­ture. The smaller the aper­ture, the greater the depth of field, and vice versa. This is one of the rea­sons that por­trait pros use ‘fast’ lenses with large max­i­mum aper­tures, as they make it eas­ier to achieve a shal­low depth of field, with the sub­ject’s eyes sharp and the fore­ground and back­ground beau­ti­fully blurred. Em­brace blur Although you might not be able to achieve the wafer­thin depth of field and soft, creamy blur of an 85mm f/1.4 lens that costs more than a grand (though see page 83 for a bril­liant sec­ond­hand op­tion), there are some sim­ple steps you can take to get the shal­low depth of field look with an in­ex­pen­sive kit lens. For a start, make sure that there’s a con­sid­er­able dis­tance be­tween the sub­ject and the back­ground, so that the back­drop is pushed far be­yond the depth of field. Shoot­ing to­wards a ‘clean’ back­ground that’s de­void of dis­trac­tions will heighten the ef­fect, as will zoom­ing the lens to its long­est set­ting.

The closer you fo­cus the lens, the shal­lower the depth of field, so move in as close to the sub­ject as ap­pro­pri­ate. As a fi­nal touch, in­clude fea­tures that are close to the front of the lens to pro­vide a dif­fuse fore­ground and make the sharp sub­ject ‘pop’ from the im­age (see above). Wildlife pho­tog­ra­phers of­ten use this tech­nique by shoot­ing through grass and other veg­e­ta­tion, but it can be used for por­traits and ac­tion im­ages too. Of course, when you’re deal­ing with a shal­low depth of field there’s less room for er­ror when it comes to fo­cus­ing. To en­sure sharp shots, choose an aut­o­fo­cus point, po­si­tion it over the most im­por­tant fea­ture (such as the eyes in a por­trait) and mag­nify the im­age on the rear screen to check for sharp­ness.

Set a large aper­ture, get up close to ob­jects in the fore­ground and fo­cus be­yond them to sand­wich your sharply-fo­cused sub­ject be­tween a dif­fused fore­ground and a dis­tant, blurred back­drop

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