Will a 85mm 1.2 or a 135mm 1.4 produce the biggest bokeh? It depends of the background distance
Hi everyone,
I was looking into reviews of the new Sigma 135mm f/1.4 lately and kept seeing references to its '100mm entrance pupil' making it the bokeh king. In comparison, a 85mm f/1.2 has an entrance pupil of 'only' 71mm, 30% less.
I decided it was time for me to properly understand what determines bokeh size (i.e. the size of the circle of confusion) in practice. I designed this interactive simulator to compare lenses (and cameras): https://romaincr-git.github.io/bokeh-simulator/
It has 2D and 3D previews which allows you to play with the distance of the subject and the background. It also includes light grids at two distances: the distance of the background, and infinity. These grids display the size of the bokeh (aka the circle of confusion / blur disk) and give the answer to the question I asked in the subject of the thread.
Basically: the entrance pupil (which is simply the focal length divided by the aperture, e.g. 135/1.4=96) does determine the size of the bokeh at infinity. So longer focal lengths and larger apertures play an equal role. Additionally, the size of bokeh increases linearly from the subject (the focal plane) to its maximum, creating a cone.
However, this is only relevant if you compare two lenses focusing at the same distance. If you compare two lenses at the same framing (e.g. a headshot), a lens with a shorter focal length (or the same lens on a larger sensor) will be closer to the subject and have a wider cone, and thus a larger bokeh, if the aperture permits.
The simulator shows that a 85mm f/1.2, despite having a much smaller entrance pupil, has a slightly larger bokeh when the background is near. However the 135mm has a significantly larger bokeh at infinity. Said differently, the near background is blurrier on the shorter lens and infinity is blurrier on the longer lens.
Now, the difference is small at short background distance and large at infinity so in real life the 135mm will likely 'win'.
My takeaway is that in practical shooting situations with a background a few meters from the subject, the difference in bokeh between a 85mm f/12. and a 135mm f/1.4 will likely be insignificant.
Hopefully this little simulator will be useful to others as well. I developed it with these two lenses in mind but it it also useful to compare whole systems (e.g. full frame versus 6x7).
Happy to have feedback for improvements. Let me know if you spot any error.
Jul 21, 2026 at 01:18 AM
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