Which have better bokeh, zooms or primes?


Right from the start it should be clear that there is no general answer to this question. As is often the case, circumstances are critically important. Which specific lenses are being compared? Are you comparing widest aperture vs widest aperture or are you stopping down the prime lens? Are you looking at bokeh circles or bokeh of a shot with busy background (foliage for example)? These and other factors play a role.

I have taken shots with the Sigma 135mm f/1.8 Art and Sigma 100-400mm f/5-6.3 Contemporary (at 135mm, of course) just for fun, which we are going to examine carefully down below. “Just for fun” because there is no fair way of comparing lenses which are as different as these two. The 135mm has a widest aperture of f/1.8 while the 100-400mm at 135mm has a widest aperture of only f/5.6 – this is a huge difference of more than 3 aperture stops. Keeping that in mind, how are you supposed to present the shots of the two lenses side by side? I have opted for the following method: f/1.8 vs f/5.6, f/2.8 vs f/5.6…and same aperture values for both lenses starting with f/5.6.

Let’s first take a look at the photos with a busy background. The Sigma 135mm f/1.8 Art is always on the left, the 100-400mm f/5-6.3 C on the right. Sorry for the different framing. I only had a lousy tripod at hand, which gave in under the weight of the 100-400mm. Since the 100-400mm doesn’t have a tripod collar, the combo is fairly front heavy.

Sigma 135mm f/1.8 A @ f/1.8 vs 100-400mm f/5-6.3 C @ f/5.6

 

Sigma 135mm f/1.8 A @ f/2.8 vs 100-400mm f/5-6.3 C @ f/5.6

 

Sigma 135mm f/1.8 A @ f/4 vs 100-400mm f/5-6.3 C @ f/5.6

Sigma 135mm f/1.8 A @ f/5.6 vs 100-400mm f/5-6.3 C @ f/5.6

Sigma 135mm f/1.8 A @ f/8 vs 100-400mm f/5-6.3 C @ f/8

Sigma 135mm f/1.8 A @ f/11 vs 100-400mm f/5-6.3 C @ f/11

Let’s take a look at the bokeh circles. The 135mm is again on the left.

Sigma 135mm f/1.8 A @ f/1.8 vs 100-400mm f/5-6.3 C @ f/5.6

Sigma 135mm f/1.8 A @ f/2.8 vs 100-400mm f/5-6.3 C @ f/5.6

Sigma 135mm f/1.8 A @ f/4 vs 100-400mm f/5-6.3 C @ f/5.6

Sigma 135mm f/1.8 A @ f/5.6 vs 100-400mm f/5-6.3 C @ f/5.6

Hardly surprising the 135mm f/1.8 has a better ability of blurring the background at widest aperture. In addition the bokeh circles, also at widest aperture, are larger and nicer, even though there is a noticeable propensity for so called cat eyes. What is surprising, however, are the results are identical aperture values. Even while pixel peeping one cannot discern an advantage for the 135mm. Btw you can find all of the pictures in full res over on flickr. 100-400mm’s bokeh circles at f/5.6 are even nicer, because this is the widest aperture for the zoom. The 135mm, on the other hand, must be stopped down more than 3 stops, which makes it impossible even for curved aperture blades to retain a perfectly round form. But that’s not all. Most zoom lenses rely heavily on aspherical lenses, which lead to so called onion rings or other more or less ugly imaging artifacts. With the 100-400mm this is different. It has quite beautiful bokeh circles, which are similar to those of the 135mm and which have no onion rings and hardly any “outlining”.

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