HD Pentax-DA 20-40mm F2.8-4 Limited
Bokeh
With its rounded blades, the 20-40mm's aperture diaphragm has an impressive ability to turn even the busiest or brightest objects into smooth, soft, and pleasing background blurs. While bokeh is a highly-subjective matter, we don't think it would be the stretch to say that the 20-40mm has the smoothest bokeh of any current Pentax zoom. Combined with its close minimum focusing distance, this makes the lens excellent for close-ups, and to a lesser extent, portraits.
The aperture diaphragm is almost perfectly circular when stopped down slightly
It turns out that the F2.8 or F4 aperture settings (depending on focal length) are just fast enough to provide the user with flexible control of the background blur when shooting close-ups.
To illustrate the beautiful bokeh that this lens delivers, we've photographed four test subjects at key aperture settings. Click on any thumbnail in the tables below to enlarge it, and then browse using your arrow keys.
20mm | 40mm | |
| F2.8 |  | --- |
| F3.5 |  | --- |
| F4 |  |  |
| F5.6 |  |  |
| F8 |  |  |
| F11 |  |  |
| F16 |  |  |
| F22 |  |  |
| F32 | --- |
|
40mm | 40mm | |
| F4 |  |  |
| F5.6 |  |  |
| F8 |  |  |
| F11 |  |  |
| F16 |  |  |
| F22 |  |  |
| F32 |  |  |
Verdict
Bokeh is one of the strong points of the 20-40mm lens, and it has been a while since we've seen a zoom lens this good at close-up photography. This sort of bokeh rivals that of Pentax's best prime lenses, though the comparatively-short focal length of the 20-40mm combined with the somewhat slow maximum aperture setting may be a bit restrictive for some applications, such as portrait photography.
