Bokeh with hard outer edge

[Fine_Art]

On my visit today I saw a lovely scene "Apple Orchard" Clearview, Ontario
My jaw clenched a bit as if from nails on chalkboard looking at the bokeh. It has this hard outer edge which seems mechanical, as if looking through the vision of robotic aliens on a rural pasture. Why do some lenses do that? Surely no lens designer would think it is natural looking.

Can someone help us by explaining what causes it? Why is it done when other lens designs seem to have no problem being very sharp with a more Gaussian bokeh?

I have no doubt its a great looking lens with wonderful sharpness for in focus objects. To me personally it detracts on a good image like this. The simple beauty of life is distorted.

Examples added from the web (not mine, please right click for source)

Hard outer edge


Neutral, even disk


Soft outer edge, more light to the center of disk


Extreme, bokeh designed lens

[MarkL]

The bokeh torture test is back lit foliage like that with small bits of light coming through, even great bokeh lens will struggle.

[Fine_Art]

I don't think it's the back lighting. Here is a shot I buggered up with too much OOF foreground. It does show how the lens puts together the light in front and behind the focussed area. The yellow is also slightly clipped so that is as much light as the system could handle. The lens still stays creamy like most Minolta lenses or Leica lenses.

[Fine_Art]

Here is a screen shot of the raw converter in MSPaint. This is just the cheap plastic kit lens that comes with the camera. Its actually a miracle I used this because I almost never carry it. It's junk compared to the old minolta primes. Still it has a silky quality to the OOF with more emphasis on the interior.

There is definitely a difference in design philosophy to the lenses of different manufacturers. How one look vs another is achieved I have no clue. All I know is some lenses let you fall in to the image with bokeh. Some look strange (to me at least). Maybe its me.

[scooby70]

In the first set of images in the OP the first shot looks to have by far the strongest backlight. I've just been checking some of my own images and I can find examples of harder bokeh taken with pretty much every fast lens I own and they seem to be the images with high contrast and strong light. I therefore think it's mostly down to a combination of strong lighting and a conducive background.

[Fine_Art]

Vignetting comes to mind. Is that affected by strong light or is it a property of the lens design?

[BartvanderWolf]

Can someone help us by explaining what causes it? Why is it done when other lens designs seem to have no problem being very sharp with a more Gaussian bokeh?

Hi ,

It's due to design trade-offs (sperical aberration correction), and the foreground bokeh is often different from the background bokeh.

Cheers,
Bart

[Fine_Art]

Hi ,

It's due to design trade-offs (sperical aberration correction), and the foreground bokeh is often different from the background bokeh.

Cheers,
Bart

Good article, thanks.

[Glenn NK]

I've always found this article to be interesting, although it requires a full and careful read to get the most out of it:

http://www.rickdenney.com/bokeh_test.htm

Some of his conclusions may not fit the knowledge or beliefs of some of us.

The article posted by Bart is also a good read imo.

Glenn