HD Pentax-D FA 150-450mm F4.5-5.6

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 blades. Their number and shape will influence the look of the bokeh, especially around highlights and light sources.

Like most recent Pentax lenses, the 150-450mm features 9 curved aperture blades, which should offer superb results regarding bokeh. Longer zoom lenses are able to compress the perspective, and to create shallow depths of field. For instance, with a subject 10 meters away, at 450mm and F5.6 the depth of field will be approximately 17cm. 

Bokeh Test

In order to evaluate the characteristics of the background blur, we took pictures at varying apertures, using these test parameters:

Results are directly transferable to APS-C cameras.

	Pentax at 160mm
F4.5
F5.6
F8
F11
F16
F22

Highlights are nicely rounded and nicely defined, without being overwhelming. Darker areas show a smooth texture on the edges of shapes (look at the lamp post). There is really nothing to complain about. The background blur will be unobtrusive in most shooting situations.

Here are further real-life examples of how the lens handles background blur.

F6.7 - Click to enlarge (Full size: JPEG, DNG)

F5.6 - Click to enlarge

Verdict

The 150-450mm delivers a smooth and visually pleasing bokeh, devoid of harsh transitions. Highlights are well rendered.  Because of the rounded aperture blades, starbursts will not appear.

Further examples of the performance of this Pentax lens can be found in the sample gallery near the end of this review.