More on bokeh (Was: Re: PESO: 3D pop?)

Igor PDML-StR pdmlstr at komkon.org
Mon Oct 5 13:10:07 EDT 2020


Toine,

First, let me say that you've got a very nice image!

Paul has given a very simple explanation for the visual effect you (we) 
observe. The further difference is (as Paul and a few others pointed out) 
comes from the quality of the bokeh for the particular lens.

As you probably know, the lead (actually, lead oxide!) in the lens glass 
raises its refractive index. This allows for thinner lenses for a given 
focal length. However, glass with a higher refraction index has higher 
dispersion that needs to be corrected to make the lens achromatic (i.e. to 
minimize chromatic [and spherical] abberations).
So, the combination of these factors *can* affect the bokeh.

I've found this informative write-up on B&H website:
https://www.bhphotovideo.com/explora/photography/tips-and-solutions/understanding-bokeh
It gives a nice overview of what and how plays a role in the bokeh - with 
some nice illustrations.
In particular, I didn't know that there are lenses with adjustable bokeh.

Now, I was curious about how much is known scientifically about bokeh.
It is clear that at least some lens manufacturers pay attention to it.

While I didn't do a deep comprehensive search in the scientific 
literature, it seems, - not much seems to be published on that topic.
I've been able to find a few research articles adressing the theory and 
theoretical calculation of the bokeh, but there are literally handful of 
those. (And there was some research on how to fake bokeh, - I assume aimed 
at creating "creative filters" for the phone-shooters.)

Of those, one paper I looked at was  Viktor P. Sivokon, Michael D. Thorpe
Optical Engineering, 53(6), 065103 (2014). 
https://doi.org/10.1117/1.OE.53.6.065103
(Sorry, it requires paid access. Feel free to contact me directly for 
detail.)
They were able to model bokeh mathematically (analytically) and compare
to the actual bokeh produced by lenses with a reasonable accuracy.
Here is one of their results:
http://42graphy.org/misc/BokehCalculated-SivokonThorpe.jpg

Cheers,

Igor


Toine Sun, 27 Sep 2020 10:56:03 -0700 wrote:

Yes I agree thats the main effect. However this guy even includes lead in
glass as a pop factor. The rendering of bokeh also adds to the effect.
Zooms have a busy bokeh.


https://photographylife.com/the-death-of-beautiful-rendition-and-3d-pop-on-modern-lenses

I can hardly see the difference in his before after shot with the slider

On Sun, 27 Sep 2020, 18:46 Paul Stenquist, <pnstenqu... at comcast.net> 
wrote:

> What is seen as 3D “pop” is just limited depth of field. And because
> primes generally have a larger app wide open than zooms, they give you 
more
> control over DOF.
>
> Paul
>
> > On Sep 27, 2020, at 10:44 AM, Daniel J. Matyola <danmaty... at gmail.com>
> wrote:
> >
> > That certainly does "pop"!
> >
> > Dan Matyola
> > *https://tinyurl.com/DJM-Pentax-Gallery
> > <https://tinyurl.com/DJM-Pentax-Gallery>*
> >
> >
> >
> >> On Sat, Sep 26, 2020 at 2:54 PM Toine <to... at repiuk.nl> wrote:
> >>
> >> I read a lot about primes vs zooms and old designs of primes. That
> >> should result in something like 3D pop. Never noticed it until today:
> >>
> >>
> 
https://www.repiuk.nl/albums/new/#&gid=1&pid=005-899-20200926-imgp3095-edit
> >>
> >> I find myself lugging the DA*300 around on a daily basis. Maybe 
because
> it
> >> pops.
> >>
> >> Do I need new glasses?
> >>
> >> Toine



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