Here's a crazy idea...apertures w/ gradients

[Bruin]

We're used to seeing lens apertures with opaque blades forming a circular (more or less) hole in the center. But instead of a sharp, well defined aperture, what if it were graduated? Something like a center filter but MUCH more extreme (going from completely opaque at the edges to transparent in the center), replacing the traditional lens aperture.

How would this affect the depth of field? What kind of images would it produce, and how would the bokeh look?

What if the aperture were a spot filter instead? (dark in the middle, light around the perimeter)

[nksyoon]

This article about bokeh shows the effect of a mirror lens (which has a dark centre with the light entering the lens in a annular/doughnut shape.

http://www.pbase.com/wboth125/image/48258606.jpg
http://www.bobatkins.com/photography/technical/bokeh/mirror2.jpg

http://www.bobatkins.com/photography/technical/bokeh.html

[Anupam]

How would this affect the depth of field? What kind of images would it produce, and how would the bokeh look?

I bet if you took a series of images at various apertures and piled them up as layers in PS and then gave each the relevant opacity, you could simulate this scenario. Not worth the effort though, IMO

[antiquark]

This might be of interest to you:
http://www.diyphotography.net/diy_create_your_own_bokeh

Not exactly what you're talking about, but I'm sure your idea could be implemented using this technique.

[R2-D2]

Have a look at Minolta's (now Sony's) 135mm STF lens...

[lZr]

Have a look at Minolta's (now Sony's) 135mm STF lens...

.....or the same with Dynax/Maxxum 7 STF mode (multiple stream of exposures)

[R2-D2]

.....or the same with Dynax/Maxxum 7 STF mode (multiple stream of exposures)
Yes, but this mode only works with static subjects. Nevertheless it's an interesting thing to experiment with...

[Brian Sweeney]

A number of lenses had aperture disks with holdes drilled into them for something like this. I've never owned one.

You could try to make it yourself- I would try with a cheap lens- remove the aperture blades and drill small holes through them. How's that for wild and crazy...

[lZr]

A number of lenses had aperture disks with holdes drilled into them for something like this. I've never owned one.

You could try to make it yourself- I would try with a cheap lens- remove the aperture blades and drill small holes through them. How's that for wild and crazy...

You can buy one ready made - Lensbaby. Taka a look here:
http://www.lensbabies.com/training-center/forum/list.php?1

I like the mood and use the ver 2.0 with my SLR and DSLR

[DelDavis]

This article about bokeh shows the effect of a mirror lens (which has a dark centre with the light entering the lens in a annular/doughnut shape.

Do the manufacturers really call them mirror lenses? It seems like an oxymoron to me. That device looks like what I would call a Schmidt-Cassegrain telescope.

[nksyoon]

Do the manufacturers really call them mirror lenses? It seems like an oxymoron to me. That device looks like what I would call a Schmidt-Cassegrain telescope.

http://photo.net/learn/optics/mirrors/tamron500-8a.jpg

http://en.wikipedia.org/wiki/Catadioptric


This would be a good walkaround lens:
http://www.canonfd.com/mirrorlenses/pages/page10.html
http://www.canonfd.com/mirrorlenses/pages/page11.html

Notice the camera on the right hand side.

[Avotius]

Yeah, seems you could do this easily enough if you were handy with a lens baby. Since their apertures come out and you can customize them it should not be that hard eh?

[bmattock]

Let's talk about why we have apertures in the first place.

They serve three purposes:

1) Control the amount of light striking the recording media during the period of time the shutter is open.

2) Allow for creative control of focus by manipulating depth-of-field effects.

3) Take advantage of optical physics which allow light scatter and falloff to be minimized at certain apertures and diffraction avoided.

You could conceivably come up with a means of decreasing the amount of light striking the recording media, as you have described. This would account for item 1 on my list. It would certainly have some effect on #2, but I do not know what that effect would be, and whether it would be useful or not. "Bokeh," as we commonly use the term in the West, has come to mean pleasing rendition of OoF areas of a photograph. This is a byproduct of DoF techniques. I suspect it would not have a desirable effect on #3, but I really don't know - I suspect it would take experimentation to find out.

You really deserve some credit for thinking of this. When apertures were first developed, waterhouse stops were used, and the leaf-blade aperture we know today came later. In each case, however, the opening was either clear or opaque - probably due to the lack of ability to control or vary a semi-transparent light blocker.

Give it a try! It would be interesting to see what effect it would have.

[Bruin]

Thanks for the great links and information, everyone. Experimenting with a Lensbaby is a great idea, since it has removable aperture disks. Just cut out some ND gel filters and stack them up...

I gotta check out this STF idea - sounds pretty cool.

Regarding the mirror lens - does it still have a traditional aperture? I wonder what would happen if your aperture were a "target" pattern (bullseye with concentric rings) :D

If the final image can be considered a stack of layers taken with different apertures and assigned varying opacities, I imagine the effect would be rather surreal. Imagine a tree in the background of your picture. Will you see a mostly OOF image with a hint of outline and details? I don't know :confused:

[Bruin]

Looks like Minolta has already thought of this with their "apodization filter." Clever trick of dyeing a negative element to achieve the gradient effect!

http://www.magnuswedberg.com/index.php?doc=STF-review

To: <Minolta@yahoogroups.com>
From: David Kilpatrick <iconmags at btconnect dot com>
Date: Thu, 14 Feb 2002 11:37:31 +0000
Subject: Re: AW: [Minolta] Re: Just received the 135/2.8 STF lens

It has a centre graduated filter in the middle of the lens next to the iris. Clear in the middle, darker to the edges. It is not a coated or dyed filter, but is actually shaped (negative) lens element. By making the lens element out of grey tinted glass, the thicker edges of the minus lens are denser than the thin middle bit. Simple idea, quite brilliant. It means that wide apertures have a graded edge to the iris shape, instead of a clean circle, but small apertures are not affected and there is less speed loss. It looks a bit like a 'centre filter' as sold for Super Angulon wide angle lenses.
I supposed someone must have ordered a pair of -3 dioptre Ray Bans and noticed that they are clearer in the centre than at the edge!


Minolta owns a huge number of really strange and exotic patents, including many acquired or bought from inventors and photographers. A guy in New Zealand sold them an entire greyscale zone system metering patent for viewfinder displays, not yet used.


The STF might be their own, it might be one they were offered. It is certainly unique. I am not sure if the whole graded effect is achieved by glass thickness though (this is what they told me).


David Kilpatrick

[R2-D2]

Looks like Minolta has already thought of this with their "apodization filter." Clever trick of dyeing a negative element to achieve the gradient effect!
Yes. The Minolta STF is the real "King of Bokeh".

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

[lZr]

Bruin, it is impossible mission to imitate the Lensbaby mood. Not in Photoshop either. This lens can deliver 3D blur/focus effect. You see left side of the image in focus, while other side blured in the very same optical plane.

[Holmz]

Let's talk about why we have apertures in the first place.

They serve three purposes:

1) Control the amount of light striking the recording media during the period of time the shutter is open.

2) Allow for creative control of focus by manipulating depth-of-field effects.

3) Take advantage of optical physics which allow light scatter and falloff to be minimized at certain apertures and diffraction avoided.

You could conceivably come up with a means of decreasing the amount of light striking the recording media, as you have described. This would account for item 1 on my list. It would certainly have some effect on #2, but I do not know what that effect would be, and whether it would be useful or not. "Bokeh," as we commonly use the term in the West, has come to mean pleasing rendition of OoF areas of a photograph. This is a byproduct of DoF techniques. I suspect it would not have a desirable effect on #3, but I really don't know - I suspect it would take experimentation to find out.

You really deserve some credit for thinking of this. When apertures were first developed, waterhouse stops were used, and the leaf-blade aperture we know today came later. In each case, however, the opening was either clear or opaque - probably due to the lack of ability to control or vary a semi-transparent light blocker.

Give it a try! It would be interesting to see what effect it would have.

The lens baby thing and the lens with a mirror won't work.
Those are cutting into the front aperture, and you really want to affect the light when it is defocused inside the lens.

But I'll answer #3.
In short - it would be favorable!
If you look through a newtonian telescope you see those pretty starlike crosses where the stars are. In reality though stars don't have crosses.
The cross is diffraction from the piece holding the secondary mirror.

Using a graduated edge would decrease the diffraction and produce (theoretically) less flair and more contrast.
I have seen filters like that for large format, but they are darker in the center and thinner on the edge to minimize vigneting.
It would work, just it would be hard to have a partcially transparent mechanism that worked at high f# and didn't scrape the coating off.

I think apodizing might be the term used. A lens does a 2D fourier transform, at the speed of light, so the mathematicians would be able to do the math.
http://www.cs.unm.edu/~brayer/vision/fourier.html

[Bruin]

Holmz brings up a good point - location of the aperture within the lens. A mirror lens and the create-your-own-bokeh trick alter front apertures. There must be a reason why the aperture in different lenses is placed where it is. Minolta's apodization filter (where the light is defocused in the lens) is the closest to what I was thinking, otherwise everyone would be sticking a strong center filter on the front of their lens to get smoother bokeh.

That's a very technical yet fascinating webpage, Holmz.

[Brian Sweeney]

It's the Image Processing HAT CHICK! I haven't seen her in over 15 years!

http://www.cs.unm.edu/~brayer/vision/fourier.html

Girl of the fourier transform can be seen in the Wavelet transform as well.

http://vision.ece.ucsb.edu/publications/98SPIE.pdf

[sepiareverb]

There were some large format lenses that had perforated aperture blades, gave a soft focus effect as I recall. Never owned one, but saw one in the studio safe somewhere I worked.

[ferider]

I think it's a great idea and technically feasible with modern LCD or glass technology.

With a conventional aperture closed down, shooting at a light source will give you rays, like this (maybe shot at f8 or so):

http://ferider.smugmug.com/photos/13427456_m8Sux-L.jpg

You can count the rays in the star pattern (in this case 10 around the sun), and will find that this nr. matches the number of aperture blades (for an even number; for an odd number of blades, you have twice as many rays). Just the slightest irregularity in aperture opening will cause this. Your design idea would make this disappear.

Roland.

PS: and yes, you can explain it via Fourier transform or convolution :)