HD vs. SMC Pentax FA Limited Lenses

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.

The SMC FA Limited have always been known for their beautiful rendering. Indeed, the designers of these three lenses put specific emphasis on the rendering of the out-of-focus areas. Despite having straight aperture blades, they have always delivered pleasing results. We can only assume that the change towards curved blades will further improve bokeh.

In this section, we compare directly the bokeh of the SMC and HD versions of the three FA Limited.

31mm F1.8

	SMC 31mm F1.8	HD 31mm F1.8
F1.8
F2
F2.8
F4
F5.6
F8
F11
F16
F22

Differences between the two 31mm are minimal. The key points are smoother and more rounded highlights at medium apertures (f4 to F11). These are visible in the background. In all honesty, however, these differences will be hard to spot in many cases.

At wider apertures, there are no true differences between the two lenses.

43mm F1.9

	SMC 43mm F1.9	HD 43mm F1.9
F1.9
F2
F2.8
F4
F5.6
F8
F11
F16
F22

Below F5.6, it is difficult to find true differences between the rendering capabilities of the two lenses. At F5.6-F11, the HD version creates more pleasing highlights. Apart from that, the two lenses' rendering is essentially similar.

77mm F1.8

	SMC 77mm F1.8	HD 77mm F1.8
F1.8
F2
F2.8
F4
F5.6
F8
F11
F16
F22

Differences with the 77mm lenses are again small, but visible starting at F2.8. The HD versions produces a generally smoother bokeh, with less distracting highlights. In all honesty, a side-by-side comparison is needed to actually spot the differences.

Verdict

The switch to rounded aperture blades has had a small impact for the out-of-focus rendering. In particular, there is a subtle change to the highlights at medium apertures with all three lenses.

The most visible differences are observed with the 77mmm. That is not surprising given that longer focal lengths isolate subjects better so the difference is more easily visible.

Why are the differences not more obvious? The answer is that the shape of the iris is only one of the aspects influencing bokeh. Since the FA Limited were designed from the ground up with out-of-focus rendering in mind, it is not surprising that this single change does not have a major impact.

All in all, the differences to bokeh are small, and are probably not a sufficient reason for a photographer to replace existing SMC lenses with their HD counterparts.