Sigma 20mm f/1.8 EX DG

£520, $630 Faster than any of the zoom lenses on test, this Sigma has a widest avail­able aper­ture of f/1.8

NPhoto - - Test Team -

All three of Sigma’s DX of­fer­ings gave a strong show­ing in last month’s big test, but this FX lens feels more ba­sic. Rather than ring-type ul­tra­sonic aut­o­fo­cus, there’s no built-in ac­tu­a­tor at all. In­stead, aut­o­fo­cus needs to be driven from in-cam­era mo­tors, as are fea­tured in all Nikon FX bod­ies. An­noy­ingly, switch­ing be­tween aut­o­fo­cus and man­ual fo­cus is a two-stage process, re­quir­ing you to op­er­ate the fo­cus ring’s push­pull mech­a­nism, in ad­di­tion to flip­ping the AF/M switch on the cam­era body.

On the plus side, build qual­ity is good and the lens fea­tures a fast widest aper­ture of f/1.8. This en­ables a rel­a­tively tight depth of field at short fo­cus dis­tances, as well as giv­ing the op­tion of faster shut­ter speeds in low light­ing con­di­tions.

Per­for­mance

In our tests, sharp­ness at the cen­tre of the frame proved bet­ter at f/1.8 than from the Samyang at its widest f/2.8 aper­ture. How­ever, the Sigma’s sharp­ness to­wards the edges and cor­ners of the frame is very poor in­deed, even when stop­ping down to f/8 or f/11. This can be a ma­jor prob­lem for ar­chi­tec­tural and land­scape pho­tog­ra­phy, and any other sit­u­a­tions where you want good lev­els of sharp­ness across the whole im­age frame.

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