Beautiful Bokeh

August 24, 2015 in Information

This lovely shot of a Pied Wagtail by Bob Brown illustrates how good bokeh is favoured in a nature shot, picking out the subject clearly.

This lovely shot of a Pied Wagtail by Bob Brown illustrates how good bokeh is favoured in a nature shot, picking out the subject clearly. A 500mm lens with 1.4x converter was used, giving 700mm and a very small depth of field.

Bob’s picture illustrates very well how a blurred background can help to make your subject “stand out”; it is a favourite technique of nature and portrait photographers especially. A lens which produces a lovely even background blurring is said to have “good bokeh” (we didn’t have a word for it, so borrowed from the Japanese). All other things being equal bokeh is improved by bigger apertures and longer lenses. This is something to watch out for in switching from a full-frame DSLR to a smaller format mirrorless system, as many are doing. You will need to go for faster lenses to get the same bokeh.

Why? Well, a 23mm lens on a Fuji X camera is said to be equivalent to about 35mm on a full frame camera such as the Canon 5D III; the angle of view is the same (your picture covers the same area). But the 23mm at any given aperture will give a less blurred background than the 35mm because its depth of field is greater. To blur the background to a similar degree you will need a larger aperture. This is why the top Fuji lenses tend to be f1.2, 1.7 etc, where the Canon lenses are often content with f2.8. (Bigger apertures put the price and weight up).

A quick look at any depth of field calculator will illustrate this. For example;

Fuji Pro-1 (1.5x crop) with 23mm at f2.8 focussed at 20 ft; everything from 12ft to 57ft is suitably sharp (Depth of field of 45 ft)

Canon 5D III (full-frame) with 35mm lens at f2.8 focussed at 20ft; everything from 14ft to 34.5 ft is suitably sharp (Depth of field 20.5 ft).

You would need to open up the Fuji lens to f1.8 to get the same depth of field, or bokeh.

So this is why the wedding photographer who switched from Nikon 70-200 f2.8 (full frame) to a (roughly equivalent) 50-150mm f2.8 on a Fujifilm camera posted a video declaring that the bokeh on the Fuji lens was poor. It isn’t, it’s physics.

 

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