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PostPosted: Wed Feb 18, 2009 7:29 pm    Post subject: Reply with quote
This sample is a good example of not producing discs.

http://www.the135stf.net/samples3.html#galleries/new/stfv2/alienEggMan_WRvanStraalen.jpg

Really good site if one is interested in this unique lens design.

/ Jan


PostPosted: Wed Feb 18, 2009 7:37 pm    Post subject: Reply with quote
luisalegria - I also find myself using longer focal lengths.

The other day I actually found myself thinking about my 50mm as a wideangle...... And that was on a cropped sensor. Very Happy

/Jan


PostPosted: Wed Feb 18, 2009 8:35 pm    Post subject: Reply with quote
It's a fantastic concept.
Not for everything to be sure but, who of us could not find such a tool as useful as any of our others.
I would like to see some samples with extreme harsh OOF highlights.
The sample gallery seems to be mostly quite subdued in terms of potentially distracting images.

Hey Chris
Nice subject. Thanks for bringing it to the surface. Very Happy


PostPosted: Wed Feb 18, 2009 8:52 pm    Post subject: Reply with quote
Wormhandler wrote:
This sample is a good example of not producing discs.

http://www.the135stf.net/samples3.html#galleries/new/stfv2/alienEggMan_WRvanStraalen.jpg

Really good site if one is interested in this unique lens design.

/ Jan


Hi,

This sample is a good example of PRODUCING BETTER discs.
The main actor in "bokeh" rendering is the distribution of brightness within Airy disc.
Airy disc is the "optical pixel" and each picture consist of infinite amount of such discs.
STF lens does good job as there we can see Gauss distribution.

some details:
about bokeh
and something related to 3D computer graphics, but good explanation of lenses, DOF and "bokeh".
about DOF rendering
more about DOF rendering


PostPosted: Thu Feb 19, 2009 8:30 am    Post subject: Reply with quote
That lens seems to have some issues, as I just found in that professional test here (quite a bit LCA for instance):
http://www.photozone.de/sony-alpha-aps-c-lens-tests/390-sony_135_28


PostPosted: Thu Feb 19, 2009 9:04 am    Post subject: Reply with quote
Wormhandler wrote:
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.
/Jan

These results reminds be bokeh created by photoshop and not naturally looking image. Disc borders are smoothed, so the results are smooth, but overal character of the bokeh don't impress me much. OOF objects don't look naturally blurred, but their shape seems to be deformed.

Maybe the problem is the way, how the smooth bokeh is created - the bokeh is not smooth because the optical design is projected in this way, but beacause there is a second iris, which cuts something of the image - I think the "something" should be in the picture, but only in different place - and not erased.

e.g. Volna-9 doesn't produce round highlights, but its bokeh is very pleasant to me.

Last edited by no-X on Thu Feb 19, 2009 9:12 am; edited 1 time in total


PostPosted: Thu Feb 19, 2009 9:11 am    Post subject: Reply with quote
The Longitudinal (Axial) Chromatic Aberrations (LoCA) and Purple Fringing seems quite severe.

But the MTF result is impressive.

I guess you can not have it all.

All the large aparture lenses seem to have these "Longitudinal (Axial) Chromatic Aberrations (LoCA)"-problems though. Even Zeiss.

http://www.photozone.de/nikon--nikkor-aps-c-lens-tests/256-zeiss-planar-zf-t-85mm-f14-review--test-report?start=1

The largest aparture lens I have seen without these LoCA is the CV Macro APO Lanthar.
http://www.photozone.de/canon-eos/267-voigtlander-sl-125mm-f25-apo-lanthar-test-report--review

/Jan


PostPosted: Thu Feb 19, 2009 5:03 pm    Post subject: Reply with quote
Wormhandler wrote:

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.


Well put. I mostly agree.

Although, if I want to see really shallow DOF I just need to close my left eye and look over the top of my glasses with my right. And there are some strange artifacts on highlights there. (Unfortunately I can't show you what I mean. But there is some line doubling in there that I don't like, so you are not missing much)

On the other hand, the STF retains more contrast in the OOF area which makes it more prominent. The 'pile of overlapping transparent disks' rendition that we are used to does lower the contrast, which helps the background be less distracting.


PostPosted: Thu Feb 19, 2009 5:18 pm    Post subject: Reply with quote
Wormhandler wrote:
...because our eyes do not create those discs

Human eye creates disc, but brain don't pay attention to OOF areas, so we don't percieve it as markedly, as we see it in the picture. You can try it. Go to a dark room, where is any power consumer device with LEDs. Look at these LEDs (best distance is a few meters) and try to defocus your eye, or focus like watching only very close distance Wink


PostPosted: Thu Feb 19, 2009 8:43 pm    Post subject: Reply with quote
I actually tried it before I made the post. But I could not get it to look like solid discs. It is of course very hard to say for sure.
The big problem is that if I focus on something very close. It is hard to, at the same time look at the thing that is OOF. Because then the OOF region automatically snaps into focus. Very Happy

The eye of course has alot of parts that has counterparts in camera lenses.

/Jan


PostPosted: Fri Feb 20, 2009 3:36 am    Post subject: Reply with quote
no-X wrote:

Maybe the problem is the way, how the smooth bokeh is created - the bokeh is not smooth because the optical design is projected in this way, but beacause there is a second iris, which cuts something of the image - I think the "something" should be in the picture, but only in different place - and not erased..


The irises are so near to each other that optically they in practice behave like a single iris - they are just a set of completely separate manual and automatic irises. The bokeh effect is totally due to the filter lens and only really works at the full aperture, i.e., at optical f/2.8 where the light transmission falls 1.5 stops to T/4.5.

Stopped down, the lens behaves more and more like a "normal" lens as the effect of the filter diminishes, see the highlight crops in the Photozone review article. Already at T/5.6 it is hardly any better than my soft focus Radionar setup. Here is an example of my Radionar bokeh, note that the nearest highlights are slightly too near for the lens setting I used:



Here is a real-life Radionar example where you can discern different size highlight discs with strong Gaussian peaks - the filter in the Sony lens would extinguish the residual edges:



More examples and an explanation of the setup can be found at

http://galactinus.net/vilva/retro/radionar_uf.html

Veijo


PostPosted: Fri Feb 20, 2009 4:56 am    Post subject: Reply with quote
Huh?

Am I missing something here? It seems to me that the "back" iris makes the "front" iris superflous.

It seems to me you could toss the front iris completely and get that great bokeh.

So . . does a diaphram placed farther from the front element create that great bokeh?

Any thoughts?

Jules


PostPosted: Fri Feb 20, 2009 5:50 am    Post subject: Reply with quote
lulalake wrote:
Huh?

Am I missing something here? It seems to me that the "back" iris makes the "front" iris superflous.

It seems to me you could toss the front iris completely and get that great bokeh.


Yes.

Quote:
So . . does a diaphram placed farther from the front element create that great bokeh?


No. the bokeh quality is dictated by the filter lens immediately behind the iris. This filter is clear at the center and progressively darker towards the edges so that the off-center rays are attenuated relative to the rays passing the center. When the objective is stopped down, the transmission will become more uniform, the bokeh quality will deteriorate, the highlight discs will become discernible and gradually also obtain a brighter edge - just like any objective with a "normal" (i.e., bad) bokeh. The flat filter lens consists of two components made of basically same type of glass, the convex component is made of clear glass and the concave one is made of uniformly tinted glass so that the rays passing the edge will have to pass through a thicker section of tinted glass. The tint is the only active ingredient, the "lens" doesn't affect the convergence of rays any more than a flat pane of glass.

Veijo


PostPosted: Sat Feb 21, 2009 3:10 pm    Post subject: Reply with quote
vilva wrote:
lulalake wrote:
Huh?

Am I missing something here? It seems to me that the "back" iris makes the "front" iris superflous.

It seems to me you could toss the front iris completely and get that great bokeh.


Yes.

Quote:
So . . does a diaphram placed farther from the front element create that great bokeh?


No. the bokeh quality is dictated by the filter lens immediately behind the iris. This filter is clear at the center and progressively darker towards the edges so that the off-center rays are attenuated relative to the rays passing the center. When the objective is stopped down, the transmission will become more uniform, the bokeh quality will deteriorate, the highlight discs will become discernible and gradually also obtain a brighter edge - just like any objective with a "normal" (i.e., bad) bokeh. The flat filter lens consists of two components made of basically same type of glass, the convex component is made of clear glass and the concave one is made of uniformly tinted glass so that the rays passing the edge will have to pass through a thicker section of tinted glass. The tint is the only active ingredient, the "lens" doesn't affect the convergence of rays any more than a flat pane of glass.

Veijo


Ahhhh . . . .yeah.


PostPosted: Mon Feb 23, 2009 2:47 pm    Post subject: Reply with quote
I recently switched to Sony from Pentax, mostly because I wanted a relatively compact and mobile FF (the A900) with in-body SR for old lenses, but the STF definately became part of the attraction. Being a bokeh buff, I bought it and have had the chance to use it next to the new Zeiss Planar ZA and some of my M42 glass. Not unlike the sample image in this thread, I can suggest I found the bokeh to be quite unique. It is also true that this lens is perhaps the sharpes lens wide open I have personally experienced. It is this combination of completely obedient oof and impeccable in-focus contrast that deliver its strength.

I was shooting with tricky, reflected metal at work for fun. The first JPG is my post-processed final shot, the second is a 100% crop from the RAW via Sonys converter with Sony's proprietary DRO+ (dynamic range optimizer) manually tweaked. This is an in-camera hardware process so I don't feel too much like its cheating to show the crop with it on. Of course, its not actually embedding the effect in the RAW until output conversion stage, but the RAW remembers your settings with regards to its in-camera use and shows it appropriately when using Sonys RAW exporter.



100% crop - note if you will the fingerprint on the right side of the measuring band.


Of course, the resolution of the A900s sensor carries some weight on this detail, but this lens is easily a match for the Planar IQ wise and stronger at close distances.

Here are a few shots of dried winter vegetation showing snowy and lit dry foliage backgrounds. The dyamic range of the system as a whole makes the backgrounds just look muted, but there was sunshine beating down on these days.





Vilva is exactly right in his description of how this lens produces the background. When this lens is wide open, there is no iris to be seen in the image at all and only one is ever effecting the image at a time. The choice to add two apertures seems stemmed to the fact that between the ranges of T4.5 (f2.8 for dof purposes) and T6.7 is the only range in which the filter has any measurable effect on oof. After this, it is basically a 'normal' lens, so one aperture is a smooth, manual 10-bladed one for STF control, where the second is a typical 9-bladed version, activated when switching the lens in 'A' (auto - body controlled). Only when the lens is un-mounted from the camera and the apertures both close down can they simultaneously be seen.

It IS without a doubt extremely cool however Smile
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