Lens Test: Sigma 105mm
Sigma’s new ‘bokeh master’ lens aims for portrait perfection, putting most competitors in the shade
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.