Is bokeh designed?

elmer3.5

elmer3.5

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Hi, i was wondering about lens designers capabilities, and came to me this question about final type of bokeh rendering.

I know nothing about optics and designing lenses, but i supose that all optical features of a lens are achieved by means of engineering and happy ending of production.

But what about bokeh or ofa?

We konw there are differences in rendering bokeh between different lenses
Sometimes it´s swirled, soft, or whatever they´re classified, but Is it achieved by the same means of engineering or it´s an ambiguous result of that?

Let´s see what you think or what you know about this!

Thanks!
 
Bokeh is rendered in certain ways because of the overall lens design. So you can "design bokeh", yes. But I guess that in most cases bokeh is not the first thing lens designers are aiming at. It's sort of a side effect, but it most certainly is possible to design a lens with good bokeh if you want to.

Edit:

romainmassola said:
Bokeh is conditionned by the shape of the diaphragm : the more blades the rounders it looks.
Click to expand...

The shape of the aperture is actually a very minor part of bokeh. You can get the smoothest bokeh stopped down, even with a 5-bladed aperture.

Can you count the blades here? The lens is slightly stopped down and has non-curved aperture blades.

DSC_8756.jpg
 
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Krosya said:
So if you shoot wide open - how does number of the blades matter?
Click to expand...

You can have bokeh when you close the diaphragm. bokeh is just a name for blurry dots of light. So if your diaphragm is of only 4 blades and shut at f8 with a small telephoto lens like a 135mm, you'll get squarish bokeh.
For what I understood.
More details and explanations here.
 
romainmassola said:
You can have bokeh when you close the diaphragm. bokeh is just a name for blurry dots of light. So if your diaphragm is of only 4 blades and shut at f8 with a small telephoto lens like a 135mm, you'll get squarish bokeh.
For what I understood.
More details and explanations here.
Click to expand...
You can have "bokeh" at whatever aperture. Round, hexagonal or whatever. The shape of the iris is only a minor part of the out-of-focus rendering. In low contrast scenes, you'll never even see the aperture shape. Still you can have "busy" or "calm" bokeh, due to different lens design.

Here's a completely round aperture, with a very busy bokeh...

DSC_5258.jpg


And then the same lens stopped down, where the aperture is septagonal...

DSC_5255.jpg



Now, which one is smoothest?
 
Wide open

Wide open

Krosya said:
So if you shoot wide open - how does number of the blades matter?
Click to expand...

But there´s bokeh wide open, isn`t it?

That`s what i´m pointing at, wide open bokeh:)

If it´s a side effect and not the main point of the lenses capabilities then it´s ambiguous in it´s rendering and the overall engineering, isn´t it?

Bye.
 
elmer3.5 said:
If it´s a side effect and not the main point of the lenses capabilities then it´s ambiguous in it´s rendering and the overall engineering, isn´t it?
Click to expand...

Bokeh can of course be designed into the rendering of a lens. Here's a lens which' rendering design was probably focused on bokeh; the Sigma 50/1.4 wide open.

DSC_3814.jpg


It's VERY different from the the lens used in my previous examples; the Nikkor 50/1.2.

Edit: Why the heck doesn't pictures work in this thread, but any other thread?
 
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The definition of Bokeh is highly subjective. However I think what many people call "Bokeh" (especially in older lenses) is simply lower contrast and other lens aberrations. Generally lens' designers try to improve sharpness and contrast (look at the newest 50 Summicron and Summilux ASPH) and users complain they are too harsh.
 
Bokeh is more the side-effects of the trade-offs that go into the design a lens. So, a lens designer can trade-off various optical corrections to produce a targeted Bokeh.


No Examples, as this thread in is the RFF Polls forum, which does not allow images.
 
Yes, Bokeh can be a factor in the design of the lens. Japanese manufacturers have used it specifically for what they call portrait lenses.
 
Nikon made a lens that lets you control the bokeh appearance:
http://www.stacken.kth.se/~maxz/defocuscontrol/

So if they planned that, they most likely design bokeh to look a certain way in their lenses.

These days, with computer aided design, then can probably plug in a specific bokeh style, and the computer will spit out a lens that produces that bokeh.
 
Bokeh is an artifact. And until relatively recently, nobody gave a damn about it. Now we elitist photo snobs are obsessed with it. Most folks are interested in the in focus areas and don't think a moment about what the out of focus areas look like.
 
Pickett Wilson said:
Bokeh is an artifact. And until relatively recently, nobody gave a damn about it. Now we elitist photo snobs are obsessed with it. Most folks are interested in the in focus areas and don't think a moment about what the out of focus areas look like.
Click to expand...

Until relatively recently, nobody gave a damn about color photography! Technology evolves, and so do expectations.
 
If I remember correctly, the transition of in-focus to out-of-focus areas can be designed, e.g. short transition (focus "snaps-in") and longer transition (focus gradually gets sharp) by the caustic (diacaustic) of the lens. A lens never focuses a point-shaped light-source into a spot but a small disk in the focal plane (airy disks) due to spherical and astigmatic aberrations. Actually it is not a disk but like a tube perpendicular to the focus plane with a neck, the neck being the "focus point" ("caustic tube"). If this neck is rather long, usually the transition between focus and out of focus is more smooth and a more pleasing bokeh can be obtained.

For SLR lenses, where the focus has to be determined by the image itself on the ground-glass, a short transition between oof and in-focus is desired. For lenses used in RF cameras, where focus is determined by an external system (rangefinder), a longer transition ("longer neck") can be chosen in designing the lens.
 
Saw an interview with the head of the optics dept at Leica.

He said they designed the new S2 lenses for good bokeh.

So yes, they have control and they are aware people look.

Nikon has made similar statements reguarding the new 24 1.4
 
Gabor, great explanation. It's a little over my head but I'm going over it a couple more times. Thanks.

Gregory
 
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