HD Pentax-D FA 28-105mm F3.5-5.6 ED DC WR

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 which 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.

Photo by wtlwdwgn shot @ 105mm, F8 (click to enlarge)

Notice how in the photo above, everything that's out of focus is nice and smooth, both in the foreground and in the background.

With the ability to focus on subjects just 50 cm away, the 28-105mm turns out to be a solid choice for close-up photography.  At its minimum focusing distance, the lens delivers a maximum magnification of 0.22x (roughly 1:5).

Bokeh Test

We ran the lens from the widest aperture down to F22 at both ends of the zoom range.  Click on any thumbnail to enlarge and browse the gallery corresponding to that focal length.

	28mm	105mm
F3.5		N/A
F4		N/A
F4.5		N/A
F5.6
F6.7
F8
F9.5
F11
F13
F16
F19
F22

Overall, the bokeh is nice and smooth until small apertures such as F16.

Note that the 28-105mm can be stopped down to F38 at 105mm, but we did not include this and other intermediate apertures above as they are seldom used and prone to diffraction.

Verdict

While the 28-105mm is neither a macro nor a wide-aperture lens, it works well for close-ups and delivers pleasing bokeh.  At 105mm, F5.6 suffices to deliver a very strong background blur.  This lens is thus a good choice for on-the-fly portraits and close-up nature shots.  We are happy to see that Pentax decided to fit this lens with a modern, rounded aperture diaphragm, as the positive effect of this clearly shows.