What makes good bokeh?

Started Apr 10, 2013 | Questions thread
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Re: What makes good bokeh? Design, incl distance of blades from rear element...
In reply to Juned D Prasetyo, Apr 10, 2013

Juned D Prasetyo wrote:

I just curious. What exactly is make some lenses give a more pleasing creamy bokeh than others? With the same focal lenght and aperture. Some said the more aperture blade give more round aperture therefore, give more pleasing bokeh. But what if both lenses set on the widest aperture? Which ofcourse not involving any aperture blade shape. Is it because of lens material? Or are there other reasons?

My understanding, albeit I am only an amateur and have NO design technical knowledge, this is from reading a bit on lenses..especially older ones...

- the immediate answer is the aperture design, including number of blades and shape. The reason for this is that as one stops down, the more blades and shape lend to a smoother shape i.e. roundness....allegedly. Some of the older Russian lenses have about 12 ot more blades and yes, they are known for smooth bokeh.

- something not often mentioned, seems to be the distance of the aperture blades from the rear element. There is a lens, cant remember which, that has a longer aperture to rear element distance, and the bokeh is butter smooth, I think the blades are not too many, nor specially shaped, so that is why someone mentioned anecdotally, that as possibly the reason for the lovely bokeh. Thinking about physics, that may make sense as the light rays have a longer travel after the blades, thus may become more dispersed, before hitting the rear element to become directed to the sensor. Thus, any shape abberations are smoothed out?

- sharpness vs bokeh. While the Zeiss lenses may be evidence against, some sharp lenses seem to have harsh bokeh. I have seen lovely bokeh from such as the 70-200 VRII in images, but some images have some 'hmmmm' bokeh. While some not so renowned lenses have lovely bokeh.

But then, look at Zeisss...they seem to have it all? But they are made 'amply. Also, the Nikkor 60mm 2.8 G and the Sigma 150mm 2.8 are both tack sharp and have lovely OOF rendering, from images I have seen.

I suspect the real reasons is a combination of the three i.e. overall design and element placement, aperture blades and location of aperture blades relative to the elements.

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