HD vs. SMC Pentax-DA 18-50mm F4-5.6
Bokeh refers to the quality, look and texture of the background blur. A smoother bokeh is generally perceived as being of a higher quality. It is one area where the newer design should show improvements. It features seven curved aperture blades instead of six straight ones for the older kit lens.
In order to evaluate the characteristics of the background blur, we took pictures at varying apertures, using these test parameters:
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The 18mm setting was used to benefit from the wider apertures available with the two zooms. The scene provides a mix of lights and lettering, at varying distances. Click on the images to see larger versions.
Even at F4, the improvement brought by the rounded aperture blades is visible, especially on the bright circles. At every aperture, the 18-50mm performs better in this regard than the 18-55mm. It will deliver more pleasing out-of-focus patterns. Looking at the red panel on the left and the windows on the right (top), the older design still holds its own for less defined shapes. It also creates pleasing starburst effects at very small apertures. The two lenses still have relatively narrow apertures and cannot be expected to compare well with more expensive portrait or macro lenses for subject isolation. Overall, the 18-50mm is still an improvement regarding bokeh and it does quite well even alongside more expensive lenses lacking rounded apertures.
Further bokeh examples can be found in the Samples gallery near the end of this review.