Sigma 18-300mm F3.5-F6.3 Contemporary
Bokeh
Bokeh is a Japanese term which refers to the quality, look and texture of the background blur. It does not relate to the depth of field but to the areas in the image that are beyond the range that is expected to be in focus.
A smoother bokeh is generally perceived as being of a higher quality. Bokeh is influenced by the lens design, with a significant role being played by the aperture. Its shape will influence the look of the bokeh, especially around highlights and light sources.
Modern lenses tend to use curved aperture blades, which generally produce a more pleasing bokeh. The Sigma 18-300mm uses a low number of curved blades, and does not offer wide maximum apertures anywhere on its range. As such, we expect bokeh to be acceptable but certainly not class-leading.
Bokeh Test
In order to evaluate the characteristics of the background blur, we took pictures at varying apertures, using these test parameters:
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Results at 18mm
| F3.5 |  |
| F4 |  |
| F5.6 |  |
| F8 |  |
| F11 |  |
| F16 |  |
| F22 |  |
At 18mm, the Sigma's bokeh is decent, but nothing special. The textures are a bit smeared, and highlights a bit too defined. As the aperture closes down, the lens is able to create beautiful starbursts, at least.
Results at 50mm
| F4.5 |  |
| F5.6 |  |
| F8 |  |
| F11 |  |
| F16 |  |
| F22 |  |
Things improve at 50mm. While the highlights still show strange shapes, the general look is more pleasing. The starbursts do not look quite as good however.
Results at 135mm
| F5.6 |  |
| F8 |  |
| F11 |  |
| F16 |  |
| F22 |  |
135mm delivers superbly rounded highlights at wider apertures. Their shape becomes more defined, but still nicely shaped, around F16, where hints of starbursts show, without deterring from the general quality. F5.6 at 135mm certainly looks better than at wider focal lengths.
Results at 300mm
| F6.3 |  |
| F8 |  |
| F11 |  |
| F16 |  |
| F22 |  |
The same findings apply at 300mm: bokeh is more pleasing than at wider focal lengths. Starting at F8, the highlight's shape becomes more defined but the shape looks nice, in an old-fashioned way perhaps.
More examples can be found in our Samples Gallery.
Verdict
At wider angles, the Sigma 18-300mm's bokeh is average, no more. Highlights take on strange shapes and the background texture is mushy.
Longer focal lengths deliver better background separation, of course, but also much more pleasing highlights.
