Talk for the 37TH Annual SPSE Conference
by Eric Howlett — May 21, 1984
How Aberrations of the Film Image are Used to Neutralize Lateral Color and Distortion in the Magnifiers of the LEEP System of Ultra Wide Angle Stereophotography
I realized while reviewing my notes just now that, if I hadn't been somewhat intimidated by this gathering I'd have called this paper “Wide-Angle Stereo — How Spectacular it is and How You Can Make it Cheap and Easy,” because that's really what the purpose of my visit here is.
The starting point for wide-angle stereo was 60 years ago next month, when a Dutch colonel named van Albada presented a paper before the Optical Society of London entitled “Wide-Angle Stereoscope and Wide-Angle Viewer”. He had an achromatic magnifier. (He was well known for making wide-angle achromatic magnifiers — they were marketed by Zeiss under his name) And he used this achromatic magnifier to make a stereo system using fisheye lenses, (he didn't call them fisheye lenses, they were “landscape lenses” in those days,) but using fisheye lenses in the camera.
If I turn this thing on we have my little sketch of the eye of a fish, which will help to define what I mean. If you take the interface between two media of differing index of refraction and the ratio between the incident and the internal angle you have a basic relationship that turns out is quite common to all lenses, which is the fisheye relationship. You see that it also holds here — If we take a plane surface and cut out a hollow back we preserve the same Alpha-Theta relationship we had with the fisheye and you can also make a camera quite easily with a plano-convex lens, preserving that same fisheye relationship. As a matter of fact it turns out it's kind of difficult to make a linear wide-angle lens. If any of you are lens designers here, you know that getting one with a 110 degree coverage and a linear relationship in the angles behind the lens and in front of it, is very, very difficult. The point is that fisheye is very easy to do. It's a very common phenomenon and a very simple-minded lens system can give you something approximating the fisheye result.
I have some curves here, which illustrate that point in a little more detail. If we plot the angle of the ray in the object space against the distance from the axis on the image plane, of course if you plot a tangent you have a linear system. If you plot a perfectly straight line you have what I call the ideal fisheye system where the distance on the film is proportional to the angle in the object space. With a plano-convex lens, if you get close enough up to it you can actually have a situation where, as the angle increases, the radius will decrease inside the camera. Between here and here fall a variety of lens systems that are awfully easy to make. The ideal for my purposes for the LEEP wide-angle stereo system is shown there in red. It's roughly where the radius is proportional to Theta minus 1/6th of the third power of Theta, so you have that third power element, and that is very easy to do. By putting the stop in the right place with almost any plano-convex lens you could do it.
Now you may not want to use a plano-convex lens for a variety of reasons, but in principle you could make a camera and a viewer just about like this. With a conceptual camera on top that has an aperture stop over here, and creates an image on the film plane, it of course has lateral chromatism as well as the distortion we've been talking about. If you take the aperture stop off and put the center of your eyeball where the aperture stop was and scan around you'll see a perfectly undistorted replica of the original scene, and the lateral chromatism, because you're looking through the same edge of the same lens, will be restored to a degree.
Now if the color film were a perfect spectrum analyzer you could restore it completely. But the color film isn't; the color film response to a full spectrum is three colors: red, green, and blue—roughly dividing the spectrum into three parts. So you don't get a complete restoration of the white color of the image. Well you get the white color back, but you don't get a complete restoration of the detail. The detail is blurred somewhat at the edges, but as a practical matter in the system that I’m explaining to you today, it doesn’t make an awful lot of difference. There will be fading off of detail at the edges but you still get a very pleasant picture to look at.
So this is roughly what van Albada did, except of course in his case he had to use achromatic lenses in both the camera and the viewer. After his presentation (he had also a demonstration out in the lobby, I imagine,) people said very nice things during the discussion: "The highest and most charming expression of stereo that we have seen," and so on. So it's natural to ask why it wasn't more popular. “Why haven't we had thousands of wide-angle stereo systems since then?” And while, of course, I don't know absolutely why not, there are two rather good clues. I'll quote an answer to one question at that meeting. He was asked when a camera would be on the market or, how you could get a camera, and his answer was, "I have not put a special wide-angle stereo camera on the market because several types presently in use can easily be made fit for the purpose." So he expected his user of the system to run out and buy something like a Roleidoscope and take the lenses out and put in some lenses that were "landscape" lenses, which would make the kind of images that were needed to view with his viewer.
Whether Zeiss shared that attitude or not I don't know, but obviously it wasn't conducive to a mass-market system. And the other thing is the cost. He only had black and white film to work with. His lenses had to be achromatic both in the camera and the viewer, otherwise he'd lose an objectionable amount of detail on the edges. Also, he only went after 80 or 90 degrees. What I'm talking about here is 150 degrees on the film, and perhaps, depending on how much you move your head, 120 degrees in the viewer. So you have a real sense of surround when you look at the picture. So as to why it didn't become popular, I think it's a question of not producing something that people go out and buy and it being very expensive to make the system in any event, because they had to use the achromatic lenses.
My invention, which I am describing to you in a few minutes, is one that allows you to make these pictures without achromatic lenses. There are two plastic lenses in the camera and two or three in the viewer and you can get a picture that's very acceptable, as you may have seen if you've been out there in the lobby, and if you haven't seen it yet, please do before you go.In fact it was in 1978. I had been interested in the idea of wide-angle stereo, assuming that you had to use achromatic lenses, and had bought a bunch of them from Edmund Scientific. I was fooling around with them, I’ll get organized here, and was bemoaning the high cost of the achromatic system when it occurred to me that you could probably avoid achromatizing the lens if you put some sort of correction in the film. I said, “I wonder if the camera lens will do that if it’s a crummy enough camera lens.” I couldn't sit down and figure it out on paper, so I ran down the cellar and got a lens, projected the image of a light bulb on a screen through the corner of it with an aperture, looked through another lens through the corner of that, and sure enough the white light buib that had become a spectrum on the screen was indeed a white light bulb again as I looked through the second lens. Could someone turn on that bottom projector for me? And I guess that — who turns off the lights? OK. What I saw that day was something —
Oh, I threw this slide in because before this day I had satisfied myself that this sentiment, which is one that you see quite often, or did then see quite often, "Wide angle lens are not suitable for stereo photography,” is very wide spread. This is a gadget you can still buy to make stereo pictures with a 35mm camera.
Anyway I knew that was a joke and, at the time I finally got to a point where I had an invention, I made up a little series of vertical lines of light and took a picture of them through a prism and obtained what you see here, which doesn't have much blue in it but you can see a red, a green, an overlapping red and green, giving yellow light. That was projected on the screen. Then when I looked again through the edge of another lens I saw this. Now this picture was actually made last week by Ulrich Figge, who is sitting over there, from the one you just saw through the same prism that the one you just saw was taken with. It's not a perfect reconstruction of the white light but it’s pretty good and it serves to answer questions and reservations that many people have about the system, who say that color film is not linear enough, or something, to allow you to do this degree of superposition. In fact it works quite well because, while here it fills up the whole screen, we are really talking about a second order effect — we just want to trim away some color fringes at the edges, and that it does very well. It gets rid of the color beautifully. It doesn't restore the full definition but it restores it adequately. The next slide — well these next few, illustrate the point. Here is an overall picture of what the stereograph looks like, except that it doesn't have its mounting frames — some boats down on the Charles. Here's one that was made with a lens that has a little more lateral chromatism that we now use. I’ll show you in a minute an enlargement of the chain in the fence. Here we go. Now you can see, I think, fairly clearly here the yellow, magenta and cyan images of that chain-link fence. Now those are fused, indeed when you look through the edge of the lens into a black, black line. Ok, you can do the lights.
The fact that indeed this works was established at that point and I proceeded to do some design to make it a more practical thing, and what I came up with after going back to my college textbooks at some length was a disposition of the set of major aberrations that went like this. The first three: spherical, coma and longitudinal color we would get rid of by stopping down. In fact we do a little more than that — there is a little surface getting rid of 2, 4 and 5 are needed to neutralize the color (the ones that are labeled in red). We need to neutralize the magnifying lens because again, the starting point, the tail that wags this whole dog, is the magnifying lens. You want as enormous a wide-angle in the lens as you can afford to make, and to do that you leave the lateral color in it — you don’t try to achromatize it, or much anyway, and of course you need the distortion not only to be able to use a cheap lens but to get two decent-sized images in the co-planar format of a practical stereo pair. So we need 4 and 5. With 6 and 7 it turns out if you use a lens combination like this — well indeed with thin lenses, in fact, of equal power positive and negative, the astigmatism and the curvature would be zero theoretically. (And that's regardless of the position of the aperture stop) These are not thin lenses, they are a bit thick, but still they tend very well to give you a field, a very respectable flat field over the region required for the 150 degrees on the film. (Whoops, the other graph please. Thank you.)
This now is the angle of the image in object space. This is the film plane itself and the various lines are the primary and sagittal images. I have a little trick of the four S's: the sagittal, the secondary image, the spoke is in focus, and it's stationary. So the ones with S don't move around very much. We had a stop here at 3, 6 and 9 millimeters, and you can see that S has only moved from there to there, and in the course of that p, the primary focal plane, is flopping all over the place. (This is where the rim of the wheel is in focus; but it turns out that over this range we have everything, both primary and secondary, in focus within a few millimeters for 37mm lens. For those of you who are lens designers, that's not too bad a performance for a field of 150 degrees, and this is in two elements, two pieces of acrylic. So we have in the camera (we have the parts of the camera in there), In the camera we're using between f/8 and f/4.5. At f/5.6, you get a pretty decent picture for portrait purposes and so on. It's not exactly what you would call a high quality 35mm image, but it gives you nice soft spherical aberration — it's not bad. It's a very good lens in two elements and the whole point of that is it makes a very cheap camera — two plastic elements about that big around, one of them (gestures) around the other (genstures), and you can put them in a box camera and take pictures with it and get exceedingly good results.
I would give you a similar description of the viewer lens but I'm advised by counsel because we haven't filed a patent application yet we'll lose some of our foreign coverage if I do. It's not quite so cute as the camera lens. It's a modified Ramsden ocular, basically, with one correcting element that serves to flatten the field, but if you look through the viewer out there (this is not the one that we would be filing application on) you'll see it’s a very fine, wide, field. One of them focuses so you see that you are not getting much change from center to middle as you run that focus up and down.
So that really is the end of the technical presentation. I have two cards here, one of them labeled “The LEEP Experience” and one of them labeled “The Mass Market." (I forgot to take my watch out so don't know how I'm doing with time. I've got about 15 minutes? Oh well! You’re going to get the pitch.
The card that says LEEP Experience means that I keep trying to tell people this is not like using an ordinary camera — even the ordinary stereo camera — the effect of having the extra angle gives you a difference in kind, it's a qualitative difference in the whole photographic concept, visualizing. You walk down the street with this thing and look at buildings, you look at the beautiful piece of architecture. You're out in the country, you look at beautiful piece of scenery. You're on top of the mountain or in a plane looking out the window. You can take these pictures back with you. With an ordinary camera you have to think, “Well, will it fit? Can I get close enough? Can I get far enough away? Where in the frame will it go?” With this thing, what your eyes behold you can take home, if you want to. So when you get to a beautiful set of mountain ranges — I am sure everyone here has had the experience of sitting back and looking at pictures when they get home and all they are all a bunch of horizontal lines with bumps on them. That's your wonderful set of mountains, (laughter). Well you do this with a LEEP picture, it's not like that at all. It takes you back to where you were. You have no focal length selection because the focal length must be the same as the one in the viewer — a requirement of orthoscopy in stereo systems. You have no perspective worries because you can't change the focal length of the lens. You have no heads cut off because the scene is so wide that you can't possibly do it unless you drop the camera, (laughter). You have no big noses, because I can take a picture from one inch — well, can't focus that close, but from 15 inches away, and your face is in the right proportions and the background all around you, the room, is all in the right proportions too. You can't get too close. You can't get too far away in a sense because if you can see it with your eyes at all, you can see it in the stereo system. The magnification of the system is unity — you get things the same size as when you saw them. So basically you have many fewer disappointments, which leads me to the last card which says The Mass Market LEEP.
There are a lot of people who feel that this is a very specialized thing, and among people who love stereo best we have some of the worst offenders, because they tend to say stereo is for or the insider, for people who know about this stuff, but the people who say stereo is something to listen to, right? — are the ones that we're talkin about and they have a much more openminded, if you'll forgive me, attitude toward this. They look at this and say, "This is great! Why aren't millions of these things around?” I don't know the answer to that question and I haven't — I think we can't determine the answer to that question. I think we can't get millions of them around without first making some and getting them out there. My definition of when there will be a mass market LEEP is when you have as many of them hanging from the necks of tourists as you now have instant cameras.
That camera that's hanging from the necks of all these tourists will probably use negative process 35mm film in a format that's maybe like a 126 cassette with two square images, not side-by-side, but one interposed, so you have a group of four. Or maybe a disc. A disc lends itself very nicely to this stereo. And it will be negatives that you take, (the exposure control will not be all that great a la the Kodak disc cheap camera). The latitude of negative color will allow you to make prints on something, and this is a key point, 70mm release print film or equivalent, 70mm motion picture release print without the sprocket holes. We can't get Kodak to eliminate the sprocket holes in order even to try it, but maybe Fujii will for us. (laughter) The release print film can be processed, I am told (if you get rid of the black stuff on the back), in a regular print processor, including benzyl alcohol and everything. It might be that we could have one projection printer in all our local processors who could take the stuff, the 35mm film, run it through, do the projection prints on to a piece of 70mm release print film, which then gets run through the paper print processor, and mounted. When you do this, by the way, you don't have to cut apart or swap the images; it stays in one piece because the reversal is automatic when you do the printing — you print through two lenses. And you could have a mass market process, a mass market system with processing locally. All that would be needed is one printer, and there are a lot of people who are able to make that printer.
The last thing that people object to sometimes when I talk about this mass market is that people will not look through viewers. One simple answer is, people will look through viewers if there's something interesting enough to look at and if the pictures are some you've made yourself, they tend to be quite interesting to you — especially if they are of yourself, or of your children. Another answer is that the viewer duplicates the paper print social situation (that we have now) better than slides. In other words you sit around casually. Slides are not as popular as prints, now — Why? Well, another case of wild speculation, but I think it's because it's easier to enjoy them.
You can sit around the table with friends and pass the prints around and talk about them, or not look at them, look out the window, talk about something else, watch the TV, whatever. It's a casual, relaxed social situation, whereas when you get your friends all in row to watch a screen in a dark room saying, "You're going to see these pictures which I have decided are pictures that you are going to like." You have a situation that many people avoid… successfully. (loud laughter) I think this thing, where we have a viewer on the table, which people can look at or ignore if they wish, but it is certainly a thing that tends people to ask, "What Is It?". ...is one that is more like the print situation. They will say, "What Is It? Well, look for yourself... and here's another one... and look at this one...” and so on. You’re into it. Your photographs are now being appreciated.
So I think the answer to the viewer as a problem is simply to turn it into an asset by looking at it that way. And last, the point that people who know stereo overlook is that when you get this wide angle, where you don't have any other reference outside — the room you can barely see (you put good horse-blinders on there to make sure of that) — what you're looking at is more like the thing itself than it is like a picture. (applause) Thank you very much.
Geoge Stein: Are there some questions for Eric? Yes.
Q. Is it possible to project the visual that you had out in the lobby out there?
A. Yes, it is possible. I think it's totally impractical, but I have a standing offer out to anyone who wishes to construct a hemispherical screen that I will give them the paper design of a projector to project these things. The point is the thing has to be an enormous wide angle. You can't do it en an 8x10' screen unless you sit about 12" to 20" away from it. You've got to have a hemisphere to accept a decent sized audience. It's the size of the screen that's the problem. And the curvature — if you tried to do it on a flat screen you'd have an awful job of getting enough light out to the edges to reflect back.
Q. Have you talked to the people at IMAX format?
A. I don't believe I know those people — What was it again?
Q. The theatre at the National Aerospace Museum.
A. Oh, I've heard about it.
Q. Fisheye projection on the inside of the dome, 70mm.
A. Yes, Omnimax is like that also. I saw that at Las Vegas. It's sensational, it's wonderful and you could do that in principle. I'm not talking to people who want to do that, I don't think. I'm talking to a mass market.
A. Yes, you could in principle make 70mm movies using this, but I don't think you need it. Unless you're trying to make something cheap, you really don't need this. You can put 3-D on a hemispherical screen with fancy lenses and so on (you could afford to spend a lot on the lenses) — you don't need to be able to make a camera for manufacturing cost of $5 or something like that.
Q. The viewer. Is that the prototype model that you have with three viewing stations?
A. That is sort of a prototype. The ones that will be shipped with the camera... We are selling them mail order now. We have orders now — we haven't started shipping them yet.) The ones we will be shipping will have two heads. Otherwise they are just about identical.
Q. How long will you be exhibiting here?
A. We'll leave it here throughout the show. And we're going to be here between two and four every afternoon — at least — during the show. One thing — for people who are seriously interested in — whatever… licensing — we are going to make some prints (transparencies) to give away with a little plastic lens so you can look at the color correcting phenomenon — take it back with you. We have — how many we going to make Ulrich? — Eighteen. We have as many as 36 of those to give away.
George Stein: Thank you very much. I would encourage you to go out and look at this system. It is very interesting. Has some very interesting phenomena.