Swirly Bokeh: Modifying Lenses Non-Destructively to Get it

[dh003i]

Hi all,

Swirly Bokeh Modification of a Lens: Pictures (http://www.tabblo.com/studio/stories/view/1747919/)

Thanks to various posts by people in these forums and elsewhere online, I think I've figured out a way to get swirly bokeh patterns on any lens. It is just caused by physical vignetting of the rear element; this causes oblique light bokeh patterns (closer to the edge) to have a cats eye effect:

To get the swirly effect seen in the shots below, I used a Minolta Rokkor-X 50/1.4 with my Olympus E-3. The Rokkor is connected to the E-3 via an adapter. (this is important, as the adapter puts a little space between the rear element and the E-3 body, so I can tape on the hole.

I cut out a circle, and cut a hole in it, and taped this to my rear element. The hole in the circle is smaller than the rear element. Hence, there is physical vignetting on the rear element of the lens. This seems to "obstruct" light entering obliquely, causing a circular cats eye bokeh pattern (swirly bokeh).

It was of course a sloppy circle, so the bokeh patterns, even in the middle, are imperfect circles. And it didn't produce a lot of swirl, so maybe I need to make a smaller circle to produce more vignetting and swirl effect. I want something like the Petzval lenses -- see here http://tinyurl.com/petzval -- whereas if you look at my shots, the swirliness is mild compared to the Petzval (the Petzval has that level of swirl near the middle of the image, and much more at he edge).

I think the Petzvals produce this effect because of the nature of the barrel lens, which obstructs light when you require a wide coverage.

PS: Also, by putting a cut out in front of the lens, as I do to create these heart-shaped bokeh patterns (http://www.tabblo.com/studio/stories/view/1747790/), you can change the shape of the bokeh pattern (although not in a way that creates swirliness). If you leave the aperture diaphram wide open, and place a cutout shape in front of the lens, that effectively acts as the diaphram (as long as it is within the "effective" aperture in front of the lens). This opens up the possibility for creating perfectly circular bokeh, as well as any pattern you want.

[Alan Davenport]

Is the "Robin" photo done with your modded lens or with a "real" Petzval? If that's your lens, you've certainly come up with a great idea!

EDIT: I reread and I guess that's a Petzval. Your color shots still rock.

I assume your mask goes behind the lens? I.E., between the rear element and the film? Do you have the mask in contact with the element or spaced away from it, and if so what happens when you vary the spacing?

Thanks for sharing.

[Dan Fromm]

The image you posted isn't nauseating, so doesn't have real swirlies. And I don't see the effects of mechanical vignetting either.

Have you considered using retouching to get the effect you want? Or painting, instead of photography?

I have a 100/6.3 Neupolar that is a reversed tessar (pair of singlets behind the diaphgragm) that's relatively long and whose elements are in a relatively narrow tube. In shots taken at distance (yes, I practice lens abuse too, the Neupolar is macro only) the result is pronounced mechanical vignetting off-axis; it doesn't have the coverage it should. No swirlies towards the edges of the area it illuminates.

dh003i, I think you've let wishful thinking take control.

[GPS]

...
dh003i, I think you've let wishful thinking take control.

Not only, but this "invention" is also in disagreement with the basic optics rules.
Oh, the level of this forum...

[dh003i]

Is the "Robin" photo done with your modded lens or with a "real" Petzval? If that's your lens, you've certainly come up with a great idea!

EDIT: I reread and I guess that's a Petzval. Your color shots still rock.

I assume your mask goes behind the lens? I.E., between the rear element and the film? Do you have the mask in contact with the element or spaced away from it, and if so what happens when you vary the spacing?

Thanks for sharing.

Yes, the mask is behind the lens, to create the slightly swirling bokeh. (for the heart-shaped bokeh ones, that mask was in front of the lens).

The mask is in contact with the element, which is why I'm doing this on a cheap 50/1.4 lens (Rokkor 50/1.4 is $30); but it is just black origami paper, and is just flat with the rear element, so I don't think it damaged it anyways. When I perfect this, I will use a piece of black micro-fiber suitable for cleaning lenses to make contact with the rear element.

I haven't tried spacing it from the rear element, but I presume that would be just the same as making the mask smaller. I'll have to try with a piece of black velvet cloth, layering it, to see if that has a different effect than just making he "hole" smaller.

I should also play around with this on my large-format 135/3.5. It will be much easier there, as the rear element has its own protrusion, and doesn't need to screw into anything.

So yea, I want to play around and see what will cause the swirliness to increase. My only suspicion, which must be correct, is simply that a larger rear obstruction would cause more swirliness. After all, his is a 35mm-format lens being used on a 4/3rds body; so half of the image circle isn't used.

[GPS]

Hi all,

...
Thanks to various posts by people in these forums and elsewhere online, I think I've figured out a way to get swirly bokeh patterns on any lens. It is just caused by physical vignetting of the rear element; this causes oblique light bokeh patterns (closer to the edge) to have a cats eye effect:

...

Good grief!

[Jim Michael]

Have you tried multiple holes in your mask?

[Archphoto]

A bit like a reversed Imagon ????

Peter

[dh003i]

Not only, but this "invention" is also in disagreement with the basic optics rules.
Oh, the level of this forum...

Well, actually, this "invention" (I'd call it a hack) isn't in disagreement with "basic optics rules". Maybe the claim that it is producing a swirly bokeh is in disagreement with "basic optics rules". I don't see the need to be insulting. In fact, I have not found a single good clear explanation of the cause of swirly bokeh, here or elsewhere. Some claim it's the lens' coma (this is verified by images (http://www.rangefinderforum.com/forums/showpost.php?p=1003332&postcount=709), although it's a different kind of "swirliness" than Petzval lenses, more like a tear shape), others the vignetting from the rear element & the aperture being wide open, some claim it can be reproduced by attaching a cheap wide-angle adapter to the front of a lens (this may be confirmed, I've asked a user of a Yashica A, who has a swirly portrait shot (http://www.flickr.com/photos/fresquez/3428196046/?addedcomment=1#comment72157620330282205),

In fact, given this discussion of vignetting and cats eye effect at the edges of an image circle (http://toothwalker.org/optics/vignetting.html), I would indeed agree the results I see are puzzling, IF I'm not imaging things. So it could be the case that my 50/1.4 has a little bit of swirly bokeh (cats eye) naturally. It seems quite clear to me that that URL above, if you think about how the cats eye would look at the extreme peripheries, explains the extreme swirliness in the Petzval lenses. The effect starts out gradually, and in the central portion of the image, has slightly ovular cat eye shapes; then as you progress towards the edges, the cats eye gets more and more elongated. This can clearly be seen by studying this photo (http://my.net-link.net/~jsmigiel/images/technical/collodion/Robin_01a72.jpg). It isn't he case that all of the sudden, at he edges, you have swirliness. It starts out as gradual cats eye shapes, and progresses to more and more elongated.

I have uploaded a "negative control" of the same lens (http://www.tabblo.com/studio/stories/shared/31891/kmj1twshfucpz8v) (Rokkor 50/1.4) without the mask over the rear element; you can compare (it isn't a perfect control, since it's a different tree, but same basic idea; bright specular highlights in background). I also uploaded shots with a Rokkor 58/1.2 MC (shots taken are each labeled with what lens taken with). Neither had the rear mask. It seems like maybe both have a slight cats eye effect at the peripheries. Maybe the effect seems stronger with the mask? I don't know, that doesn't make sense to me.

I will have to try using a velvet material for several layers (to simulate a piece of black card-board extending the rear element).

[Nathan Potter]

dh003i, you're not nearly there as Dan pointed out. I think you need to understand the peculiar optical property that yields curved out of focus circles of confusion oriented around the periphery of the image. I believe this has something to do with extreme barrel distortion in the out of focus edge COC, but I'm just guessing. Perhaps someone here has a precise optical explanation.

Again I'm just guessing but you may make more progress by using a simple auxilliary lens element in front of or behind the normal imaging lens then refocusing to the altered focal length.

Nate Potter, Boston MA.

[dh003i]

dh003i, you're not nearly there as Dan pointed out. I think you need to understand the peculiar optical property that yields curved out of focus circles of confusion oriented around the periphery of the image. I believe this has something to do with extreme barrel distortion in the out of focus edge COC, but I'm just guessing. Perhaps someone here has a precise optical explanation.

Isn't that what I was referring to in linking to this web-page about vignetting; in particular, see figure 2 (http://toothwalker.org/optics/vignetting.html). The best explanation regarding "swirly bokeh", as far as I can gather, is that it is something present on all lenses wide open at the peripheries, as the light entering "sees" a cats-eye shape that gets narrower and narrower as the path of the light become more oblique.

I'm aware that the images I posted don't have that "nauseating" wormhole-like swirl to them. However, they do resemble the more central portions of pictures posted from Petzval shots. IOW, it is just a matter of degree.


Again I'm just guessing but you may make more progress by using a simple auxilliary lens element in front of or behind the normal imaging lens then refocusing to the altered focal length.

Nate Potter, Boston MA.

I presume you mean a wide-angle converter?* I've read that elsewhere. However, I'm not sure how that will achieve said effect.

I'm also not sure what you mean by refocusing to the altered focal length (are you simply referring to sticking a WA-converter on, and then using the lens as normal?).

* Actually, a neat thing would be some kind of auxillary rear element that alters the light exiting the lens such that it would then fully cover only the 4/3rds standard, and not 35mm.

[Peter K]

I presume you mean a wide-angle converter?* I've read that elsewhere. However, I'm not sure how that will achieve said effect.
A wide-angle converter is an afocal system that doesn't change the focal-length of the lens that is used with. But a simple auxilliary lens element as Nathan has suggested does.

But it will be hard to get the over-corrected astigmatism together with field curvature in the outer area that makes the swirl in Petzval's lens.

Peter K

[Mark Sawyer]

Hi all,
Thanks to various posts by people in these forums and elsewhere online, I think I've figured out a way to get swirly bokeh patterns on any lens. It is just caused by physical vignetting of the rear element; this causes oblique light bokeh patterns (closer to the edge) to have a cats eye effect...


I've been a proponant of this theory of swirliness at times, but now have my doubts. If this were the cause, then Rapid Rectilinears would also swirl. Mechanically, they are very similar to a Petzval in barrel construction and spacing between the front and rear elements, but to my knowledge, don't swirl. Also, some old triplet projection lenses are similar in mechanical construction to the Verito, but will not swirl at all, while the Verito will swirl like crazy.

Even my Imagon will give a hint of the swirls, and it has the shortest barrel arrangement of any lens I have. I think the swirlies are the result of the whole optical system more than one particular part.

[Jim Galli]

Sort of like building an amphibicar when a boat is so much simpler and elegant.

[goamules]

Mark, I have a Busch Portrait Aplanat f6 that I could swear I've seen swirl on. I'll go check it to make sure....when it get's below 105 degrees....if it's still daylight. Sheeze, Tucson in summer.

[GPS]

Hi all,

...
Thanks to various posts by people in these forums and elsewhere online, I think I've figured out a way to get swirly bokeh patterns on any lens. It is just caused by physical vignetting of the rear element; this causes oblique light bokeh patterns (closer to the edge) to have a cats eye effect:

...

dh003i,
take the last resting amount of your common sens to see that whatever vignetting of rays leaving the rear of a lens cannot change anything on the rays that are not "vignetted". The rays that are obscured by the vignetting obstacle don't create any bokeh either... ;)

[dh003i]

dh003i,
take the last resting amount of your common sens to see that whatever vignetting of rays leaving the rear of a lens cannot change anything on the rays that are not "vignetted". The rays that are obscured by the vignetting obstacle don't create any bokeh either... ;)

GPS,

Take the last resting amount of your common decency and courtesy to at least bother to read the reference I have linked to (http://toothwalker.org/optics/vignetting.html) (several times) explaining optical vignetting. If you feel that reference is wrong, then please explain why, or provide a reference to something that is correct.

If you have something useful and polite to say, please do. If not, no-one is forcing you to read this thread, and it shows poor manners to be continually insulting. I can only hope that the rest of your 1000+ posts have more civility in them than these do.

[GPS]

dh003i
in your case you're talking mechanical vignetting caused by an outside ring that obstructs rays leaving the rear lens element.
Whatever vignetting of rays leaving the rear of a lens cannot change anything on the rays that are not "vignetted". The rays that are obscured by the vignetting obstacle don't create any bokeh either...

[Nathan Potter]

dh003i, yes Peter K explained what I was trying to say, namely the application of a single element lens of some diopter power will change the focal length of your 50 mm lens and will require some refocusing. Peters' comment on over corrected astigmatism in conjunction with field curvature seems a good explanation for the "bokeh" effect people talk about. Of course as Galli comments it's a lot easier to go out and buy the damm lens - but then the fun and discovery in experimentation is lost. :) :)

Nate Potter, Boston MA.

[dh003i]

I've been a proponant of this theory of swirliness at times, but now have my doubts. If this were the cause, then Rapid Rectilinears would also swirl. Mechanically, they are very similar to a Petzval in barrel construction and spacing between the front and rear elements, but to my knowledge, don't swirl. Also, some old triplet projection lenses are similar in mechanical construction to the Verito, but will not swirl at all, while the Verito will swirl like crazy.

Even my Imagon will give a hint of the swirls, and it has the shortest barrel arrangement of any lens I have. I think the swirlies are the result of the whole optical system more than one particular part.

While I don't know about he Rapid Rectilinears, many fast rectilinear modern designs do swirl to a slight extent. There are the Noctilux', but also a Nikon 85/1.4 swirls: http://farm4.static.flickr.com/3310/3650807401_49b8bd317f.jpg

I think that the pictures I posted show a slight swirling of OOF points; a cats eye distortion. Clearly not as extreme as the Petzvals.

An eBay seller suggests that the bokeh signature of the Petzvals is partially due to field curvature:


"Petzval Portrait lenses do not have a field corrected for flatness. Its field is curved which creates a beautiful fall off much desired today, but this was not the effect most desired by 19th century photographers This beautiful fall off is different than the fall off and Bokeh created by flat field Anastigmat lenses with shallow depth of fields when used wide open. Many art photographers such as Sally Mann prefer early lens formulas with curved fields and optical aberrations to create interesting, atmospheric, or pictorial effects."

Someone suggested that a CRT lens (HD 6 D Delta) lens can produce the kind of bokeh pattern of the Petzvals; although I don't know how one would use it with a mono-rail, owing to it having no shutter (likewise with the Petzvals, actually).

PS: Actually, I have a Rodenstock TV Heligon 75/"1.1". Of course, it is only f/1.1 at infinity, where the image-circle is the size of a nickel or less and the lens has to be about 0.5cm-1cm from the image-plane. As I understand it, at a useable extensions for four-thirds, it would be have a maximum distance from subject of 1 foot, and would be a macro lens.

[goamules]

I'm not sure who this is I found a few weeks ago, but his Vivitar is swirling quite a bit:
http://www.flickr.com/photos/ghosstrider/3581026115/

He mentions "optical vignetting" as the cause, with his definition; "trying to make a lens cover a bigger piece of film (or digital sensor) than it was meant to."

That doesn't make much sense to me, many lenses will cover more than their recommended size, but we don't do it because of the loss of sharpness. Anyway, it's another example of a design doing the spins.

[Dan Fromm]

We dealing with people who don't have the concept "off-axis aberrations." They think that coma is comma misspelled ... and they work, possibly unwittingly, to use the Internet to spread errors.

[Archphoto]

Dan, it belongs to photography in general: experimenting with optics that are not ment for their new use......
And sometimes something usefull and interesting comes by.
LF uses at time projection lenses, fitted to shutters that were never intended for it, and we love the results.
Being curious is a part of photography, when you loose that you are just making a living or even not that.
The great thing with LF (and digital) is that you can experiment all you want.
I did some testing with the 58XL, the 72XL and the 115 Grandagon on 8x10 just to see what I could with them and found out that that the 72XL and 115 are usable for panorama's with the propper cropping in absence of having a 6x17 camera.

Peter

[Dan Fromm]

Peter, I have no problems with experiments in general or with the experiment that launched this thread, although I think what the OP sees is more in his mind's eye than in the image he posted. I'm glad that you experiment, am surprised that it took experimentation to discover that cropping to a smaller format will give the same results as shooting on the smaller format. But then, I shoot a 38/4.5 Biogon on 2x3, which it absolutely positively doesn't illuminate, let alone cover.

I have major problems with the OP's explanations of what causes the effect he wants. Also with the explanation that goamules reported and carefully didn't endorse.

Cheers,

Dan

[Mark Sawyer]

I have major problems with the OP's explanations of what causes the effect he wants. Also with the explanation that goamules reported and carefully didn't endorse.

Cheers,

Dan

Cheers, Dan! You have a good bit of knowledge in optics, and as this has been a subject of debate and speculation for some time, could you offer any insights into what specific factor or combination of factors causes the infamous "swirlies" to occur?

[Dan Fromm]

Mark, I can't offer much beyond "lens abuse," using a lens with bad (but which ones?) off-axis aberrations on a format larger than the format it covers.

That said, I have some test shots that show what I diagnose as astigmatism (manifested as different resolution with horizontal than with vertical lines) and bad distortion (e.g., vertical lines strongly slanted) at the edges of the field. Toss in a lot of coma, which gets worse the farther we go off-axis, and the combination might do it.

There's an example of, IIRC, trees floating around that's said to show the swirlies very strongly. Every time I look at it I feel queasy. And every time I look at it the nasty little voice in the back of my mind murmurs "long exposure. wind. the leaves moved."

Cheers,

Dan

[Mark Sawyer]

Darn, no clear answer there, Dan! So the theorizing goes on...

I've thought of astigmatism occurring in a circular rather than linear pattern, but astigmatism seems to happen on a fairly small scale, too small to be the cause of the big swirlies we've seen.

Mechanical vignetting (the "cat's-eye" shaped off-axis aperture) seems the most likely culprit, but the Petzval swirls so dramatically compared to the minimal-to-nonexistant swirls from Rapid Rectilinears and Aplanats which would have near identical off-axis apertures.

And they really don't look like any coma I've ever seen...

No answers here, either...

[dh003i]

Yea, everyone jumps all over me for "wishful thinking", but no-one seems to have a clear authoritative explanation and reference.

I think that the article I linked to is at least partially explanatory.

I also posted negative controls with my 58/1.2 and 50/1.4 without the rear mask. I think they exhibit some of the same effect without it too. I think it looks like the milder swirl from the Petzvals in the center of the shot.

If I cropped out those petzvals to the middle 1/3rd to 2/3rds of the shot and said there was "mild swirl", I think people was say I was hallucinating too.

[dh003i]

A bit like a reversed Imagon ????

Peter

That's another good idea. The other link I had in the 1st post was to "heart-shaped" bokeh patterns; this was caused by simply making a heart-shaped cutout on a piece of paper, and then making that a circle a little larger than the lens, and twist-tying it to the end of the lens.

I suppose a disc with a central hole and many smaller surrounding holes, like the imagon could also be made. Although I seem to remember reading someplace that the position of the diaphram matters, and that for most lenses, optimal position is where it is actually placed ("inside" the lens), and it will be sub-optimal in front of the lens.

Another interesting idea would be center spot filters, with a transparent center, and opaque edges; graduated in between. This would create silkier bokeh in highlight points, like with the Sony 135mm f/2.8 [T4.5] STF.

[Mark Sawyer]

That's another good idea. The other link I had in the 1st post was to "heart-shaped" bokeh patterns; this was caused by simply making a heart-shaped cutout on a piece of paper, and then making that a circle a little larger than the lens, and twist-tying it to the end of the lens.

The heart-shaped patterns are lens flare reflections of the aperture shape, and occur equally throughout the frame. The "swirlies" occur at the outer edges of the image circle. Two different phenomena, thugh the underlying causes may be related (or not...)


I suppose a disc with a central hole and many smaller surrounding holes, like the imagon could also be made. Although I seem to remember reading someplace that the position of the diaphram matters, and that for most lenses, optimal position is where it is actually placed ("inside" the lens), and it will be sub-optimal in front of the lens.

With a single lens grouping, the aperture's optimal position is in front of the lens. That's where it is on Imagons, Kodak Portrait lenses, landscape lenses, etc. A misplaced aperture will adversely affect field curvature and coma.

Just more unhelpful information! :)

[Dan Fromm]

Mark, you've picked up on the OP's confusion of rendition of out-of-focus highlights with what most people think of as bokeh. The OP isn't the only person who's restricted bokeh's definition that way.

I don't understand why people care about bokum, whatever they mean by the word, or why they treat it as more than a minor nuisance. I also don't understand why the OP is so concerned about what I see as a relatively minor element of image quality.

dh003i, would you please tell us what you mean when you say bokeh? An explanation of why it matters would be nice too.

Cheers,

Dan

[dh003i]

I don't understand why people care about bokum, whatever they mean by the word, or why they treat it as more than a minor nuisance. I also don't understand why the OP is so concerned about what I see as a relatively minor element of image quality.

Well, when I utilize shots with a very narrow depth of field, it does matter to me. I'm interested in either doing interesting things with the bokeh (as with the patterns I linked to, or swirly), or having a very creamy rendering of it (as the Sony STF lens does (http://photo.net/equipment/sony/135STF/) by not having a "sharp" aperture definition, but aperture blades that are transparent the center, and opaque on the outer edges, so highlights such as bright lights are rendered more creamy. See these actual examples (http://photo.net/equipment/sony/135STF/point_blur.jpg) from photos as illustrative (left is STF, right is normal lens). That is something something that could seemingly be done easily with an external filter.

Of course, when I want the entire frame in focus, bokeh doesn't matter at all, or matters only to the extent that some parts of the frame are not in focus despite my efforts.


dh003i, would you please tell us what you mean when you say bokeh? An explanation of why it matters would be nice too.

I distinguish bokeh from depth of field, and consider it to be the quality or character of the parts of the image not in sharp focus.

[dh003i]

With a single lens grouping, the aperture's optimal position is in front of the lens. That's where it is on Imagons, Kodak Portrait lenses, landscape lenses, etc. A misplaced aperture will adversely affect field curvature and coma.

Just more unhelpful information! :)

Thanks. Adversely affecting field curvature and coma seems like something that might affect the swirl on the outer parts of an image, given that I've seen that affect at least partially attributed to curvature and coma.

[Jim Galli]

I don't understand why people care about bokum, whatever they mean by the word, or why they treat it as more than a minor nuisance.

Cheers,

Dan

We're trying to fool the onlookers brain into releasing endorphins when viewing our pictures.

Dan, even you have to admit that the out of focus area made with an 8.8mm lens with 11 aspherized elements in 8 groups on a digi cam is a train wreck. OK, we're over-reacting, but it's sort of fun. Not quite as wacky as stacking 3 bellows on 2 tripods to shine a 44 inch lens on 6X9 film, but close. :D:D

[Dan Fromm]

Jim,

Thanks for the reply.

I see now where I'm lacking. Ain't got no digital cameras. Not a one. So I haven't been blessed with the experience you've kindly described. Now I understand more.

But why don't people talk about the highly desirable train wreck bokeh? Why haven't I heard about it before? Why am I always the last to know?

If its fun, that's great. But I'm sure that the doing is more fun than the talking ...

Two (2) bellows, Jim, one (1) tripod, and so far only a tiny little nineteen (19) inch (") lens of nothing at all. You desert rats all exaggerate. Next thing we know, you'll be telling us about the jumping lenses of Tonopah County.

Cheers,

Dan

[Dan Fromm]

dh003i, thanks for the response.

Please understand that I have no objections at all to your pursuit of your photographic goals. If the images you capture please you, I'm pleased for you whether I like them m'self or not.

Its your language and explanations that I have trouble with. For example, your report on Bob Atkins' report on the Sony STF lens. Per Bob, the apodizing element is a pair of pieces of glass, one plano-concave, the other a matching plano-convex. The plano-concave one has low transmission and because of its shape (thickness grows with distance from the axis) acts as a gradient filter. Bob didn't say it, but both elements of an apodizing element usually have the same refractive index. Anyway, and here's my quarrel with your explanation, the lens has perfectly normal and conventional diaphragm blades. Even worse, his test images show very little difference, to my eyes, at least, between conventional lenses and the STF.

Its nice that you concede there's more to bokum than rendition of out-of-focus highlights.

Cheers,

Dan

[CatSplat]

Even worse, his test images show very little difference, to my eyes, at least, between conventional lenses and the STF.




This image illustrates it rather well, the STF system certainly has an effect on the out of focus areas.

http://i14.photobucket.com/albums/a318/CatSplat/919d0e01.jpg

[Hollis]

The hearts would be greeeeaaaaaat for a wedding photographer (sarcasm)...

Still, cool research indeed. I always thought that the swirls and unique patterns came from the mood the old german optical polisher was in back in 1884 in a dark back room of a factory in Dresden. I can still daydream though....

[dh003i]

Its your language and explanations that I have trouble with. For example, your report on Bob Atkins' report on the Sony STF lens. Per Bob, the apodizing element is a pair of pieces of glass, one plano-concave, the other a matching plano-convex. The plano-concave one has low transmission and because of its shape (thickness grows with distance from the axis) acts as a gradient filter.

Dan, thanks for the response. I think that for the STF lens, the two apertures are pretty much unrelated to each-other. IIRC, one is controlled manually and as more aperture blades; the other is controlled by the camera in auto-mode and as less aperture blades.

What contributes to the creamier bokeh this lens offers is that the aperture elements are gradient filters, making highlight bokeh points more soft. This could, in principle, be done by some kind of circular gradient filter placed in front of a lens too.

And I think it definitely does have an effect on bokeh in highlight areas particularly; see CatSplat's post.

PS: I wonder if an aperture mask in front of the lens with a bunch of small holes punched in it (let's say f/22 size) would produce the same DOF as f/22, but while effectively letting more light in (higher T-stop).

[dh003i]

The hearts would be greeeeaaaaaat for a wedding photographer (sarcasm)...

LOL, yes, it is really gimmicky (but so are a lot of things). And of course, they have no placement in relation to the macro-subjects that were being photographed. But I imagine they could be useful for some (cute) type photos.

The more generally useful idea from that is to simply cutout a perfect circle, use it like a water-house stop, and hence not have octagonal (or 20-sided) bokeh, but perfectly circular.

Of course, as Mark points out, having the aperture in the sub-optimal place can "adversely affect field curvature and coma". Then again, might be a benefit for some types of shots.

[Mark Sawyer]

What contributes to the creamier bokeh this lens offers is that the aperture elements are gradient filters, making highlight bokeh points more soft. This could, in principle, be done by some kind of circular gradient filter placed in front of a lens too.


I'm wondering about this, based on the fairly common practice of using center-weighted neutral density filters directly in front of the lens to reduce the fall-off effect. Using a "graduated" filter is different than using a solid diaphragm that chokes the lens down to a smaller f/stop.

If you're doing this in large format, I think it would be worthwhile to search for a process lens that had a filter/aperture slot in the proper place, or an older lens slotted for waterhouse stops.

I'm also not to sure about how you'd go about making such a filter. Center filters for wide angles are somewhat challenging to make, even for the lens manufacturers, as attested to by their prices. And the negatives of putting an inferior element in the middle of the lens would likely outweigh the positives of a graduated aperture...

Crap, I'm sooooo discouraging... :(

[Dan Fromm]

Dan, thanks for the response. I think that for the STF lens, the two apertures are pretty much unrelated to each-other. IIRC, one is controlled manually and as more aperture blades; the other is controlled by the camera in auto-mode and as less aperture blades.

What contributes to the creamier bokeh this lens offers is that the aperture elements are gradient filters, making highlight bokeh points more soft. This could, in principle, be done by some kind of circular gradient filter placed in front of a lens too.

And I think it definitely does have an effect on bokeh in highlight areas particularly; see CatSplat's post.

PS: I wonder if an aperture mask in front of the lens with a bunch of small holes punched in it (let's say f/22 size) would produce the same DOF as f/22, but while effectively letting more light in (higher T-stop).dh003i, thanks for the reply. Also to the link to Bob Atkins' review.

Sigh. The lens has two iris diaphragms, one for manual aperture control with 10 blades, the other for auto aperture control. Neither is transparent. The reason for having two diaphragms has to be mechanical.

Neither diaphragm causes Smooth Transition Focus. That is caused by the apodisation element, a gradient filter that has highest transmission in the center and lowest transmission at the edges. The gradient filter is an integral part of the lens and has no moving parts. Read more about it here: http://www.the135stf.net/index.html

If you want to play bokum games with a digicam, replace your E-3 with a micro 4/3ds camera that will allow you to use lenses made to cover formats smaller than the micro 4/3ds 18x13.5 chip. I suggest replacing the E-3 because its mirror limits you to using lenses whose back focus is at least as long as the camera's flange-to-film distance. Part of the micro 4/3ds system's appeal to hackers is that it will accept lenses with very short back focus.

Then get an projection lens from an 8 mm (or maybe 16 mm, you'll have to experiment) that is a Petzval type; many, not all, are. And then you'll be able to practice lens abuse like the big boys.

You might want to do some reading about pinholes, zone plates, and photon sieves. But be aware none of these bon-bons offer high apertures. No shallow depth of field with any of 'em.

Do learn to report accurately. You give the impression, which I hope is untrue, that your reading comprehension is poor.

Cheers,

Dan

[Dan Fromm]

I'm wondering about this, based on the fairly common practice of using center-weighted neutral density filters directly in front of the lens to reduce the fall-off effect. Using a "graduated" filter is different than using a solid diaphragm that chokes the lens down to a smaller f/stop.<snip>

Crap, I'm sooooo discouraging... :(Um, Mark, the apodising element in the STF lens is densest at the edges, not in the center like the center filters we use with very w/a lenses to mitigate the effects of cos^4 (sometimes only ^3 but still obnoxious).

About being discouraging, comfort yourself with the thought that at times rain improves parades and hairdos. There's something about the fashionable bedraggled effect ...

Cheers,

Dan

[Mark Sawyer]

Um, Mark, the apodising element in the STF lens is densest at the edges, not in the center like the center filters we use with very w/a lenses to mitigate the effects of cos^4 (sometimes only ^3 but still obnoxious).

About being discouraging, comfort yourself with the thought that at times rain improves parades and hairdos. There's something about the fashionable bedraggled effect ...

Cheers,

Dan

Yup, I was aware of that, but was wondering (albeit unclearly) about the effect. Wouldn't an apodising filter in front of the lens act like a "reverse" center filter?

And the fashionably bedraggeled effect comes and goes, I suppose... :)

[dh003i]

dh003i, thanks for the reply. Also to the link to Bob Atkins' review.

Sigh. The lens has two iris diaphragms, one for manual aperture control with 10 blades, the other for auto aperture control. Neither is transparent. The reason for having two diaphragms has to be mechanical.

Neither diaphragm causes Smooth Transition Focus. That is caused by the apodisation element, a gradient filter that has highest transmission in the center and lowest transmission at the edges. The gradient filter is an integral part of the lens and has no moving parts. Read more about it here: http://www.the135stf.net/index.html

Dan,

Thanks for the correction, I did merely skim that link, although imo, that is a relatively minor technical detail. What is important is that the more creamy rendition of OOF highlights is caused by "a gradient filter that has highest transmission in the center and lowest transmission at the edges". That is the important point for me. Because these kind of gradiated filters are common.

Also, I'd read about these neat capabilities of the m43rds bodies. For me, the disadvantages of not having a prism and hence no OVF far outweigh the advantages. It is a P&S type body; you can't hold it up to your eye to shoot, which means it will be less stable; plus not weather-sealed and no articulating LCD.

It will be a long time before I consider micro-four-thirds for my own use, due to those issues. There would need to be an articulating LCD and an EVF that could act as a drop-in-replacement for an OVF (this would require a lot of resolution and very fast response-time; I anticipate EVF's won't be as good as OVFs for 10 years). Although I have recommended m43 to people who don't want an SLR, but want the benefits of a larger sensor.

[Tiziano]

I don't know which is the root cause od the swirly bokeh, but I know about one 35mm lens that generates that effect, which I sometimes find nice. It's the old Russian Helios 40, which is an 85mm f/1.5 lens.
You can see an example here:
http://i10.photobucket.com/albums/a135/tiziano_bruno/kids/_MG_7399.jpg

[GhoSStrider]

We dealing with people who don't have the concept "off-axis aberrations." They think that coma is comma misspelled ... and they work, possibly unwittingly, to use the Internet to spread errors.

I'm the guy with the Vivitar. Rather than "using the Internet to spread errors" I've changed the description on my page.

Sorry about any confusion I may have caused.

[mandoman7]

Having an 8x10 as well as an inclination to learn new techniques, I'm gratified that the genuine vintage look is not attainable with the small digital camera. Its good when the development of one's craft is actually rewarded and not undercut by generation-x pretenders.
In my observation of the history of photo equipment pricing, when you see high prices then it often is because you can't get that look without paying for it. The $1000+ pricing on the desirable older portrait lenses tells a story, particularly when you realize the shutter and mounting issues people have to deal with.

[Jim Galli]

Having an 8x10 as well as an inclination to learn new techniques, I'm gratified that the genuine vintage look is not attainable with the small digital camera. Its good when the development of one's craft is actually rewarded and not undercut by generation-x pretenders.
In my observation of the history of photo equipment pricing, when you see high prices then it often is because you can't get that look without paying for it. The $1000+ pricing on the desirable older portrait lenses tells a story, particularly when you realize the shutter and mounting issues people have to deal with.

oops! :D:D Somebody let the 800 pound gorilla out in the room. I also belive this to be true. Either that or the folks with the white jackets need to come to my house and get me.

Part of this is simply brute force of format. With the larger formats the effect has a large (huge relatively) area and lots of substrate to delicately do it's thing.

[Dan Fromm]

Jim, Mandoman7,

Larger formats are much more open to, um, lens abuse than are the smaller ones. But I think that for those inclined to tinker, micro 4/3 might offer, um, the worst of both worlds.

That said, I don't see how one can get an acceptable print much larger than roughly 5"x7" from micro 4/3. Ya want a big print, ya gotta start from a big negative.

Cheers,

Dan

[dh003i]

Jim, Mandoman7,

Larger formats are much more open to, um, lens abuse than are the smaller ones. But I think that for those inclined to tinker, micro 4/3 might offer, um, the worst of both worlds.

That said, I don't see how one can get an acceptable print much larger than roughly 5"x7" from micro 4/3. Ya want a big print, ya gotta start from a big negative.

Cheers,

Dan

Well, the lenses available for "micro" 4/3rds -- which has the same sensor size as 4/3rds, and is named horribly -- are extremely sharp. Dpreview considered the Olympus ZD 50/2 the sharpest lens they've ever tested. So that makes up for the smaller format, to a limited extent.

I have a very sharp silhouetted 12x9 print; and that was taken with a legacy Minolta Rokkor 50/1.4 close to wide open.

But of course, for enormous prints, and don't want to deal with panos, LF and the new ($45K) medium-format cameras are the only way. (also $20k digital scanning backs).

[Archphoto]

One of my friends had made a 80x120 cm print of one of my Olympus E410 shots and it looks razor sharp without any grain and has great detail in it.
Modern DSLR's have a good quality pic comming from them and the Olympus lenses are of exeptional image quality.

But this is a bit off-topic.....

Peter

[rafimoor]

Here is my explantion:

http://rafimoor.com/english/bokehe.htm

[dh003i]

One of my friends had made a 80x120 cm print of one of my Olympus E410 shots and it looks razor sharp without any grain and has great detail in it.
Modern DSLR's have a good quality pic comming from them and the Olympus lenses are of exeptional image quality.

But this is a bit off-topic.....

Peter

Yes, the DSLR's are quite impressive given their inherit sensor-size limitations. Under the right conditions, they can produce excellent quality images. However, ultimately, I think that 4x5 will always out-do them in terms of sharpness and grain, if good technique is used. Of course, DSLR images can appear sharp and grain-free, but it is subjective. By the same standards, 4x5 would appear at least as good or better (the issue being if the enlargement was big enough to differentiate).

The best Olympus 4/3rds lens that is reasonably affordable is the Olympus 50/2 macro. At f/4.0, it gets 123 lp/mm. The theoretical diffraction limit is 375 lp/mm. It thus realizes 32.8% of the theoretical diffraction limit. 123 lp/mm corresponds to an enlargement of 123/5 = 24.6x, or prints of 17.4 x 12.6 inches.

f/4.0 for 4/3rds corresponds to 4 x 6.92 = f/28 for 4x5 (6.92x might be lower than some people use, but I'm accounting for the edges not being usable on 4x5 due to the film holder guides). At f/32, a Fuji C-series 450/12 gets 41 lp/mm (http://www.hevanet.com/cperez/testing.html) or 88% of the diffraction-limit of 47 lp/mm. At f/28, it will get at least that many lp/mm. This corresponds to a print of 32.8 x 41 inches.

Despite their superb quality, 4/3rds lenses never get as close to the theoretical diffraction limit as do 4x5 lenses. By f/32 (equivalent to f/4.6 in 4/3rds for dof), 4x5 lenses can resolve to between 80 - 88% of the theoretical diffraction limit. By f/22 (equivalent to f/152 for 4x5), the Oly 50/2 gets 54 lp/mm, or 79% of the theoretical diffraction limit of 68 lp/mm.

To get equivalent sharpness, DSLR lenses would have to get to as high a % of their theoretical diffraction limits as do 4x5 lenses at equivalent f-stops for dof. To get equivalently fine grain, they would need to use much much lower ISO. At identical final print sizes (lets say 50x40in, so the differences can be seen), ISO 100 for 4x5 will produce the same image quality or grain as ISO 2 (!) for 4/3rds! (film area of 4x5 is 20 sqin, film area of 4/3rds is 0.36 sqin, hence there is a 55x difference in imaging area). Sufficed to say, there is no such thing as ISO 2 for 4/3rds, although you could take numerous identical exposures and average them to reduce the noise (IIRC, each doubling of the # of exposures reduces equivalent noise by sqrt(2)). But going the other way around, ISO 100 on 4/3rds is equal to ISO 5500 on 4x5 in terms of image quality.

[Dan Fromm]

5 lp/mm acceptable? You're blind.

[dh003i]

5 lp/mm acceptable? You're blind.

haha, well I was being generous. For the purpose of comparison between formats, what final acceptable resolution we use is irrelevant. If we use 10 lp/mm, final print sizes are just halfed for 4/3rds and 4x5.

FWIW, Chris Perez uses 4 to 6 lp/mm: (http://www.hevanet.com/cperez/results.html)


What does it take to print a lenses resolution to paper? 4 lines/mm to 6 lines/mm is all the human eye is reported to resolve in an image printed to standard bromide B&W stock (color isn't much different I understand). Given this and 47 lines/mm at f/32 you can print an image 40x50inches and _just_ reach the limits of lens/film resolution.