Double diaphragm lenses

[ChrisLilley]

Recently I was reading about an interesting lens design which has two diaphragms, one for normal aperture control and one for control of out of focus areas. The particular one I cam across was the Sony STF 135mm f/2.8 [T4.5] .

Is anyone ware of other, similar designs?

Review and explanation here (in French)

block diagram:


photo


The design also includes an 'apodization filter' which seems to be a radial gradient ND filter to counteract the vignetting of the second diaphragm. So this lens has a geometric max aperture of f/2.8, and the DOF of f/2.8, but transmission stop of T4.5 (meters at f/4.5).

Some sample images

[ChrisLilley]

more samples

[kds315*]

Interesting concept, maybe for specialists, not for "normal shooters" most likely.

[A G Photography]

[martinsmith99]

The bokeh is nice in the 1st image, but it's too in-yer-face I think. The clarity of the subject is amazing. But, I actually prefer the last image. Not as sharp, but the bokeh is toned down.

[Orio]

I don't know, the combination of deep focus on the subject + totally blurred background does not look organic to my eye, it actually gives me a dizzy feeling, example given image #4 in the posted link.

[hacksawbob]

Just had a lateral thought, why if we can have drop in filters can we not have drop in apertures? perfect round for bokeh or what ever shape you want, no blades to get stuck, would need to have a slit in the camera bodywhat do you think?

[estudleon]

It's interesant to me from the view of the avanced technology. It's too new the concept, perhaps, to have a complete idea of the real application of the lens. Nice theory.
Now, it's seems too complex for a series of relatively common takings.

May be for other man less "amateur". Possible future collector item?

Rino.

[Wormhandler]

I love the bokeh of the STF design (#1). I have heard of it before but have not seen any samples. This comparison really shows the difference.
It also allows you to work at a smaller aparture (bigger DOF and sharper in focus area) at the same time as having an effect on the background mimmicking a much bigger aparture.

Would love to get one of those.....

/Jan

[koji]

Yes, some of older soft-focus lens had "drop-in aperture" with/without
special holes to make "nicer/special" bokeh, and some of Nikon's ultra-micro
or printing lenses had those drop-in aperture.

I personally like the last two bokeh samples in the above, can't decide
which since I prefer the bokeh that retains original shape a little bit.

Some info. The top left graph shows front and back bokeh in MTF sense (contrast change)
at 2m distance with F2 aperture, defocused -0.625 (front) to +0.625 (back) mm.



This lens was introduced with Minolta A-9, 1998. So this technology was
not too new, Minolta was seeking "bokeh" since its early era, STF is
the culmination of its achievement I think.

[koji]

This lens has very small distortion and astigmatism which contributes also
a good bokeh, its spherical aberration is not small however it is rather
straight line (you can see, the most right side of graphs) so that image
plain is relatively flat.

MTF is showing good, the right side one is measured one by independent
tester, two left ones were given by Minolta. Like Zeiss' there are three
pairs of lines of 10, 20, and 40 lpm(?).

[Wormhandler]

Koji, you write:
"I personally like the last two bokeh samples in the above, can't decide
which since I prefer the bokeh that retains original shape a little bit."

But as I see it. The first (STF) example is the one that actually retains the shape the most in the OOF region. The other examples turns all OOF detail into discs, thus distorting the actual shape.

The STF bokeh reminds me of the bokeh of some of my lenses from folder cameras.

I am not saying that the Zeiss 135 1.8 bokeh is ugly to behold though.

/ Jan

[koji]

Jan, I kind of agree your observation about STF's bokeh. It seems that
STF's bokeh retains a little too much for my liking.

[no-X]

I'd prefer something between #1 and #2. The first one looks almost synthetical to me.

[Spotmatic]

I don't know... I find it hard to compare crops. I would like to see the whole photo and not just part of it. The photos are almost 95% bokeh and 5% subject.

I looked at the samples (link in the first post) and I like the bokeh. What do you think?

[lulalake]

[Wormhandler]

Koji - I understand what you are after.

no-X - About the synthetic part.
I think that we are so used to see OOF, with highlights, rendered with those discs. We even talk about how these discs should look like to create pleasing bokeh. 99,9 of all lenses renders like that.

My hypothesis is that when something do not create discs it feels unnatural and postprocessed.
If you think about it it is kind of strange, because our eyes do not create those discs. So the synthetic feeling should in fact be attributed to those unnatural discs instead.

Some random thougths that hit me.

/Jan

[martinsmith99]

Does anyone apart from photographers actually look at the bokeh?

We worry too much about what the OOF part of the image looks like. The average joe, probably takes very little interest.

[trifox]

[estudleon]

3 or 4 years before, I read a news article to a habitual jury in photography in Argentina explaining that the call bokeh, was not generally had in account to describe and to award the photographic works, but that there were other more important considerations (it named the composition, quality of impression, the novel of the approach, etc.)

Rino.

[trifox]

one more thing ---- again IMHO ...

the subject on the picture number 1 -- IS DEFINITELY SEPARATED from the background in better way that on the other 3 pics ...

and also you may have a better imagination what's on the background ..

finally - the background is EVENLY RENDERED ... IMHO..

that's the best thing that could have been happened !!

3 other examples are NOT GOOD ENOUGH in rendering of the background..

tf

[ChrisLilley]

[rawhead]

I will have to completely agree with anybody who claims that the STF lens creates, by far, the best bokeh ever to be seen on 35mm. You can't beat that smoothness. The STF lens by itself is enough to persuade me to abandon everything and move over to the Sony system.

For better or for worse, Canon just announced the TS-E 17mm F4L. And *that* is enough to convince me to abandon everything and move over to the Canon system, even over the STF

[Wormhandler]

Each time i See those 4 shots I get more and more entranced by the STF.

Some more information
http://www.the135stf.net/

And this page with samples
http://www.the135stf.net/samples.html

/ Jan

[luisalegria]

Bokeh is important to normal people, not just crazy photographers, because even if they don't analyze what they are seeing, they are getting an unconscious aesthetic impression.

This lens produces brilliant bokeh I think, smooth and not distracting from the subject. Getting this isolation of the subject may be the reason I like long telephoto so much.