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135mm STF
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PostPosted: Sun Dec 04, 2011 9:32 pm    Post subject: Reply with quote
Very interesting, I think it deserves a thread of it's own.


PostPosted: Mon Dec 05, 2011 10:13 am    Post subject: Reply with quote
Agree. It deserves a new thread.

The material with soft transition between clear and black to make the iris blades makes me think of organic eye construction.


PostPosted: Mon Dec 05, 2011 10:25 am    Post subject: Reply with quote
The bokeh of the STF looks a lot like that from a Petzval lens.

Probably the best lens to use for a DIY version would be the Meyer Primotar as it is very easy to dismantle and already has superb bokeh.

There are grad filters with a clear centre, one of those would probably be ideal.

I am working on adding an aperture to my Kershaw projector lens which has fantastic super smooth bokeh, if that doesn't give me what I want I will try adding a centre grad to a 135mm lens methinks.


PostPosted: Mon Dec 05, 2011 10:32 am    Post subject: Reply with quote
The lens images look very good, however this speech:
http://www.the135stf.net/design.html
is what we call in Italian "fried air" Rolling Eyes
if you put a dark circular filter on the edges, the effect is very much the same as stopping down the iris.
But they pretend it's a revolutionary concept Rolling Eyes Laughing
also the gradient is really useless especially at tele lenght, proximity to sensor plane makes it irrelevant if the edge
is smoothed or not, natural blur effect makes also a sharp edge invisible. Just try to put a pencil near the front glass
of a 135mm lens and look in viewfinder Rolling Eyes Rolling Eyes
(and consider that the iris is very much closer to the film plane, so blurring much more strong)
It's really true that it's easy to joke people into believing in the miracles of science Rolling Eyes Rolling Eyes Rolling Eyes


PostPosted: Mon Dec 05, 2011 12:23 pm    Post subject: Reply with quote
Orio wrote:

if you put a dark circular filter on the edges, the effect is very much the same as stopping down the iris.
But they pretend it's a revolutionary concept


It is not the same effect as stopping down the opaque iris, since the apodisation filter is not opaque but lets through gradually decreasing amounts of light on the edges of each circle of confusion, which is exactly what causes the gaussian blur effect. Also, stopping down the iris would increase the f-number, which would decrease depth of field, but the apodisation filter keeps the (approximate) f-number while costing some light and decreasing the t-number.

(Note that some people confuse the second iris inside the lens with the apodisation filter or the STF effect. However, neither iris is used for the effect since the effect is strongest with the lens wide open when both are retracted—stopping down actually reduces the effect by blocking the edges of the apodisation filter. The reason for the second iris is that it can be controlled manually with greater accuracy than by the camera's automatic settings, and it has more aperture blades since it does not need to be able to stop down as fast as the camera-controlled first iris.)


But, yes, it's not revolutionary as a concept; ZoneV posted above about having done the same (albeit after reading about the STF lens) and I've implemented a similar idea myself (after reading about the STF lens) by putting a starburst-harped cardstock cutout inside a Jupiter-9, and it works, sort of (except it has the same problem as ZoneV's experiment that sometimes the structure of the “filter” will begin to show). However, the STF is the only lens on the market with anything like this already implemented, and it is implemented by means of a special optical element—the same quality could not be achieved by just inserting an additional filter to an existing lens design. (Also note that “they” did not call it a revolutionary concept, only “unique”, which it is.)

As for the hype, the linked site is a fan-made site, not an official Sony or Minolta advertising. Actually Sony's marketing doesn't promote the lens very much, perhaps because it appeals to a very specific crowd who are willing to deal with the slow t-number, manual focus (without AF confirm because the filter confuses the heck out of phase detect AF), and a lens much larger and more expensive than your usual 135mm f/2.8.

(Personally I got the lens at about half price from eBay, but still it is very expensive for what it is. But it is also one of my most favourite lenses; I will never sell it.)


PostPosted: Mon Dec 05, 2011 12:30 pm    Post subject: Reply with quote
Arkku wrote:
Also, stopping down the iris would increase the f-number, which would decrease depth of field, but the apodisation filter keeps the (approximate) f-number while costing some light and decreasing the t-number.


I have a hard time believing that.
Stopping down an iris does no special trick, it simply blocks light incoming from peripheral areas of the glass.
A very dark filter does exactly the same, so if stopping down an iris increases, as a consequence, the perceived depth of field,
I can't see why using a dark filter shouldn't.


PostPosted: Mon Dec 05, 2011 12:45 pm    Post subject: Reply with quote
ehemm, Since when does a dark filter increase DOF??


PostPosted: Mon Dec 05, 2011 12:52 pm    Post subject: Reply with quote
If a dark filter would work the same, then why did nobody get the luminous idea to create a diaphragm consisting of nothing more than a LCD screen with variable light transmission, mimicking a real diaphragm?


PostPosted: Mon Dec 05, 2011 1:02 pm    Post subject: Reply with quote
I am confusing.

DOF should be the same for the designed f-stop.
It's like putting a dark/gray filter infront of my 50/1.2 in daylight at f1.2, right?

oh. I like the concept of LCD for vary gray filter Wink


PostPosted: Mon Dec 05, 2011 1:11 pm    Post subject: Reply with quote
kds315* wrote:
ehemm, Since when does a dark filter increase DOF??


It's a circular filter, designed to almost block the light from the sides of the glass.
A closed iris does the same, only completely, whilst the dark filter lets a little part of the light pass through.
Since reducing the aperture increases the apparent depth of field (pinhole cameras have a virtually infinite perceived DOF)
it is very hard to believe that such a dense filter (look at it, it is almost black on the edges) has no effect on the perceived depth of field,
because the working principle is the same as that of the iris (to block light from the sides)


PostPosted: Mon Dec 05, 2011 1:17 pm    Post subject: Reply with quote
Spotmatic wrote:
If a dark filter would work the same, then why did nobody get the luminous idea to create a diaphragm consisting of nothing more than a LCD screen with variable light transmission, mimicking a real diaphragm?


I'm not sure to understand what you mean, in any case, anything that you put between the front glass and the exit pupil of a lens has the effect of an iris.
Actually, even if you put something immediately before the front glass, it works as an iris, too, at least with tele lenses.
Try cutting a circle of black cardboard the diameter of your tele lens, and cut a round hole in it, to approximate a f/5.6 aperture, set the iris of the lens to wide open, and put your holed cardboard circle upon the front glass, it will act exactly like an iris and you will take f/5.6 photos.


PostPosted: Mon Dec 05, 2011 5:31 pm    Post subject: Reply with quote
Spotmatic wrote:
If a dark filter would work the same, then why did nobody get the luminous idea to create a diaphragm consisting of nothing more than a LCD screen with variable light transmission, mimicking a real diaphragm?


The apodisation filter should be placed into the iris position - and its structure shows up in the bokeh.
Furthermore LCD reduces light even when open.
And I am not sure how much stray light will be inducted from it - this is a big problem.

I am pretty sure that aopdisation filter increase DOF. And could make optical quality a bit better, because of reducted transmission of outer lens rays - so image problems are less visible.


PostPosted: Mon Dec 05, 2011 9:29 pm    Post subject: Reply with quote
Will the Tamron SP Adaptall-2 70-150mm F/2.8 SOFT Model 51A have the same effect or is it more like nikkor DC?

ZoneV,
When you modify the iris shape by adding the slide, you have then a lens with a specific/fixed iris shape/open right? If i want to modify one lens (90/100/105/135), what f-stop-slide should it be?
I have several pentax 135/3.5 that can be used for this project.


PostPosted: Mon Dec 05, 2011 11:38 pm    Post subject: Reply with quote
Orio wrote:

it is very hard to believe that such a dense filter (look at it, it is almost black on the edges) has no effect on the perceived depth of field,
because the working principle is the same as that of the iris (to block light from the sides)


“Look at it”? What “it”? Are you speaking of the DIY filter posted in this thread by ZoneV, or the actual STF lens? The apodisation element in the STF lens (which I have) is not dense at all, the gradation is quite subtle and extends close to the center of the (large) element. It is nowhere near opaque even on the extreme edges (and indeed why make a special element that turns a lens into manual focus only if the effect was the same as just installing a waterhouse stop in there). And why is the DoF at f/2.8 t/4.5 as shallow as with other 135mm f/2.8 lenses? And why, if it's the same as closing down the iris, does stopping down either of the actual irises decrease the effect while increasing DoF? =)

Last edited by Arkku on Fri Feb 07, 2014 11:27 am; edited 3 times in total


PostPosted: Mon Dec 05, 2011 11:41 pm    Post subject: Reply with quote
hoanpham wrote:
Will the Tamron SP Adaptall-2 70-150mm F/2.8 SOFT Model 51A have the same effect or is it more like nikkor DC?


It is slightly more like the DC, but not at all like either of these. See earlier in this thread.


PostPosted: Fri Dec 09, 2011 10:30 am    Post subject: Reply with quote
just got my NEX-Minolta AF Adapter Very Happy



PostPosted: Sun Dec 11, 2011 6:24 pm    Post subject: Reply with quote
In the Minolta/Sony lens, apodisation is not due to some kind of "filter", but to a 2-element optical block inserted near the optical center of the lens:


Credit : http://www3.xitek.com/testreport/xitek/135stf.htm

in this special optical block, the plano-convex element is made of clear glass, while the plano-concave one is made of tinted glass. Both have the same refractive index, thus having together a zero optical power (like a slice of glass with parallel sides). But the combination transmits more light in the center than in the periphery, because the tinted glass element is thicker (darker) at its periphery. A very clever contraption!

Cheers!

Abbazz


PostPosted: Sun Dec 11, 2011 7:22 pm    Post subject: Reply with quote
Abbazz wrote:
In the Minolta/Sony lens, apodisation is not due to some kind of "filter", but to a 2-element optical block inserted near the optical center of the lens:

in this special optical block, the plano-convex element is made of clear glass, while the plano-concave one is made of tinted glass. Both have the same refractive index, thus having together a zero optical power (like a slice of glass with parallel sides). But the combination transmits more light in the center than in the periphery, because the tinted glass element is thicker (darker) at its periphery. A very clever contraption!

Cheers!

Abbazz


Yes?

You just described a center-weighed grad filter, built into one of the optical components of the lens so that you don't have to introduce an additional filterblock (and thereby introducing more air/glass surfaces, increasing flare and random refraction/reflection).

It's a graduated ND filter, going from almost 100% transmissive in the chief ray (optical center line) to blocking ~85% (slightly more than a ND4 filter) in the marginal rays - rays from the edge of the f/2.8 aperture diameter. The grand sum of transmission is that of an f/2.8 aperture with an average of 1+1/3Ev worth of ND filtering.

That they found a way to build this filter into one of the optical blocks of the main construction does not make it "not a filter".


PostPosted: Mon Dec 12, 2011 9:51 am    Post subject: Reply with quote
hoanpham wrote:
..ZoneV,
When you modify the iris shape by adding the slide, you have then a lens with a specific/fixed iris shape/open right? If i want to modify one lens (90/100/105/135), what f-stop-slide should it be?
I have several pentax 135/3.5 that can be used for this project.


I have the filter near the iris location, it is at the moment not exactly in the iris position.

The actual iris diameter is not the same as focal lenght / f-stop!
Because of this one can work with 135 slide film for many lenses with bigger entrance pupils. I optimize the filter for wide open use. But due to the transmission shape it is still a bit bokeh sculpting at closed iris settings.


PostPosted: Mon Dec 12, 2011 3:58 pm    Post subject: Reply with quote
the_Suede wrote:
You just described a center-weighed grad filter, built into one of the optical components of the lens so that you don't have to introduce an additional filterblock (and thereby introducing more air/glass surfaces, increasing flare and random refraction/reflection).

It's a graduated ND filter, going from almost 100% transmissive in the chief ray (optical center line) to blocking ~85% (slightly more than a ND4 filter) in the marginal rays - rays from the edge of the f/2.8 aperture diameter. The grand sum of transmission is that of an f/2.8 aperture with an average of 1+1/3Ev worth of ND filtering.

That they found a way to build this filter into one of the optical blocks of the main construction does not make it "not a filter".

Of course one can call it a grad filter. In fact, it is not an "optical block of the main construction" stricto sensu, as it has zero power optically speaking (it does not bend the light rays), so it really behaves like a filter.

Cheers!

Abbazz
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