LenScore™ Bokeh
 
How to rate bokeh? Certainly a fair question, and one that is frequently asked. Most photographers have a favorite lens when it comes to bokeh, and most of those lenses are fast, medium to long primes. However, some will argue that the smooth bokeh of modern lenses is bland and boring compared to the busy bokeh of a Helios 40-2 for example, and they have a point. Stunning pictures are taken with the Helios, with weird, beautiful bokeh. These images are not great despite the flawed bokeh, but because of it. Thus, it is all a matter of taste.

Or is it? When we discussed the different aspects of a lens we would like to measure, consensus was easily reached regarding measurement of bokeh: physics. A perfect lens does not introduce any kind of aberrations in out-of-focus areas, both in front of and behind the focal plane. No geometrical distortion, no color shift, no chromatic aberrations, no accentuation or attenuation of edges; just pure, mathematically perfect blurring. But that's exactly the kind of bland bokeh mentioned above, isn't it? Yes it is, but as it happens, the vast majority of people - not just photographers - find this kind of bokeh by far the most aesthetically pleasing. It's also the most versatile, as it will never ruin a shot, it will always look good, no matter what kind of picture is taken. Unfortunately, it is also hard to achieve. The lenses coming closest to mathematically perfect bokeh are also top performers in the other categories, and they're usually on the expensive side.

So what about the Helios and all those other lenses with interesting bokeh? In capable hands, they are creative tools able of producing beautiful images impossible to take with a mathematically perfect lens, but they are not good general purpose tools. In most situations, their optically flawed bokeh will lessen the quality of a shot. It is safe to say that for all but a few special applications, clean and smooth bokeh is preferable, and that's why the LenScore™ bokeh score is based on how close a lens' out-of-focus rendering is to mathematical perfection.