GROUP TEST: BOKEH LENSES

It’s not all about sharpness. Here, we compare four legendary lenses that will give you blurred vision, in a good way…

We compare four legendary lenses that will give you blurred vision and dreamy effects

If you think about the key attributes of high-quality lenses, sharpness is probably one of the first things that springs to mind. But for portrait and still-life images, bokeh can be even more important. This is a term for the pictorial quality of defocused areas within an image. Ideally, photographers look for a really soft and creamy appearance to blur fussy backgrounds and make the main point of interest really stand out.

The first thing you’ll need in the pursuit of beautiful bokeh is a tight depth of field. ‘Fast’ lenses with a wide aperture rating are therefore the order of the day, and a longer focal length is helpful. When shooting on a full-frame camera, 85mm lenses with an aperture rating of f/1.4 or f/1.8 are often preferred, some of which we covered in a group test back in issue 220. This time, we’re going further still, looking at Canon 85mm f/1.2 lenses (old and new), along with 105mm f/1.4 lenses from Nikon and Sigma.

But there’s more to beautiful bokeh than just a tight depth of field. Although lenses with matching focal lengths and aperture rating technically give an identical depth of field, the quality of bokeh can be very different in terms of smoothness – both for defocused areas and in transitional regions between in-focus and out-of-focus points.

Colour fringing is another factor to look out for. It’s not just lateral chromatic aberration that’s a concern, as fast prime lenses can be notorious for longitudinal or ‘axial’ chromatic aberration too. This can produce a coloured fringe around objects in front of or behind the point of focus. Unlike lateral chromatic aberration, it can occur at any point across the image frame, instead of being mostly limited to the edges and corners.

Ideally, lenses should give a well-rounded appearance to defocused lights and bright spots in an image. A well-rounded diaphragm in a lens, typically based on nine or more curved blades, helps to retain this when stopping down. This is important when you can’t shoot at the widest aperture because the depth of field is too tight for the area you want to keep in focus, or the lighting is so bright that your fastest shutter speed is insufficient to avoid overexposure. Let’s take a look at our contenders…