Lens Test: Sigma 105mm

Sigma’s new ‘bokeh mas­ter’ lens aims for por­trait per­fec­tion, putting most com­peti­tors in the shade

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Sigma’s new ‘bokeh mas­ter’ 105mm f/1.4 lens aims for por­trait per­fec­tion, putting most com­peti­tors in the shade

the Canon EF 85mm f/1.4l IS USM stole the show in our su­per test of por­trait lenses, in is­sue 140. It’s a big, chunky lens that com­bines an 85mm fo­cal length with a wide f/1.4 aper­ture rat­ing, plus a highly ef­fec­tive image sta­bi­lizer. Sigma’s new 105mm beats the Canon for tele­photo reach, matches it for aper­ture width, but ditches sta­bi­liza­tion. Dubbed the ‘bokeh mas­ter’, it aims for top sharp­ness across the en­tire image frame, along with su­per-smooth creami­ness for de­fo­cused ar­eas. If you thought the 950g weight of the Canon 85mm lens was heavy for a prime lens, you might be sur­prised that the Sigma weighs in at 1645g and comes with a tri­pod mount­ing ring.

The com­plex op­ti­cal de­sign is based on 17 el­e­ments, laid out in 12 groups. These in­clude three top-per­for­mance FLD (Flu­o­rite­grade Low Dis­per­sion) el­e­ments, two SLD (Spe­cial Low Dis­per­sion) el­e­ments, and one aspher­i­cal el­e­ment. Multi-layer coat­ings are ap­plied and a flu­o­rine coat­ing is added to the front el­e­ment, to re­pel mois­ture and fin­ger­prints, as well as to aid clean­ing. Un­like many of Sigma’s older ‘Art’ lenses, this one has weather-seals, like a rub­ber gas­ket on the mount­ing plate.

As well as con­cen­trat­ing on sharp­ness and con­trast, in con­junc­tion with bokeh, the op­ti­cal de­sign aims to min­i­mize sagit­tal coma and astig­ma­tism across the en­tire frame, so that points of light are re­pro­duced nat­u­rally with, as

far as pos­si­ble, a cir­cu­lar shape. The well-rounded nine-blade di­aphragm helps to re­tain this, and to max­i­mize the over­all qual­ity of bokeh, when stop­ping down a lit­tle.

per­for­mance

The Sigma de­liv­ers ace im­ages in terms of sharp­ness and con­trast. Sharp­ness is great right into the cor­ners of the frame, even when shoot­ing wide-open. Vi­gnetting is no­tice­able at f/1.4 but isn’t bad, thanks to the wide phys­i­cal di­am­e­ter of the lens. Dis­tor­tion is neg­li­gi­ble and both lat­eral and lon­gi­tu­di­nal chro­matic aber­ra­tions are min­i­mal. The lat­ter is re­ferred to as ‘bokeh fring­ing’, which can’t be cor­rected in-cam­era or dur­ing pro­cess­ing. As with some other re­cent Sigma lenses, in-cam­era cor­rec­tions are avail­able for lat­eral chro­matic aber­ra­tion, pe­riph­eral il­lu­mi­na­tion and dis­tor­tion, when us­ing Canon DSLRS.

Ful­fill­ing its other main prom­ise, the Sigma de­liv­ers fab­u­lously smooth bokeh, and the tran­si­tional ar­eas be­tween fo­cused and de­fo­cused ar­eas within im­ages are im­pres­sively seam­less. De­fo­cused pin­pricks of light are well-rounded across the whole image frame, but can be a lit­tle prone to tak­ing on a slight onion ring ef­fect. Even so, it’s a lot less no­tice­able than from Sigma’s 85mm f/1.4 Art lens.

02 04 Big is beau­ti­ful: the crafts­man­ship on this Sigma Art lens is stun­ning 06

Switch be­tween man­aual and aut­o­fo­cus with gen­eral ease

105mm f/2 Even when nar­row­ing the aper­ture by an f-stop, de­fo­cused lights re­tain a cir­cu­lar ap­pear­ance

105mm f/1.4 The tran­si­tion be­tween fo­cused and de­fo­cused ar­eas in pho­tos is ren­dered with seam­less smooth­ness

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