pearce@alias.UUCP (Andrew Pearce) (10/06/89)
There were several 3-D films at SIGGRAPH this year which used polarization
to achieve left eye/right eye distinction.
My question is, what are the actual mechanics of placing the two images on
film? Is the film double exposed, once for each image of the stereo pair,
with different polarization each exposure? Does the film grain retain this
polarization? Or is it a special type of film with a polarized emultion on
each side?
Sign me, Just Curious,
- Andrew Pearce
- Alias Research Inc., Toronto, Ontario, Canada.
- pearce%alias@csri.utoronto.ca | pearce@alias.UUCP
- ...{allegra,ihnp4,watmath!utai}!utcsri!alias!pearce
--
- Andrew Pearce
- Alias Research Inc., Toronto, Ontario, Canada.
- pearce%alias@csri.utoronto.ca | pearce@alias.UUCP
- ...{allegra,ihnp4,watmath!utai}!utcsri!alias!pearceray@hydroplane.cis.ohio-state.edu (william c ray) (10/08/89)
Well, I may just be an idiot, and someone may have some magical way of doing 2 polarized images overlaid on the same piece of film, (and Pixars may drop to $15 tomorrow...) But if I were to do a polarized 3d film, and I'm only a punky undergrad, with no experience here, I would project *2* simultaneous strips usicross polarized polarizers, one on each projector, but what would I know? Will Ray
greg@sj.ate.slb.com (Greg Wageman) (10/10/89)
Opinions expressed are the responsibility of the author. In article <65539@tut.cis.ohio-state.edu> william c ray <ray@cis.ohio-state.edu> writes: >Well, I may just be an idiot, and someone may have some magical way of doing >2 polarized images overlaid on the same piece of film, (and Pixars may drop >to $15 tomorrow...) But if I were to do a polarized 3d film, and I'm only a >punky undergrad, with no experience here, I would project *2* simultaneous >strips usicross polarized polarizers, one on each projector, but what >would I know? Clever optics on the camera (anamorphic lenses and combiners) and the projector (splitters and anamorphic projection lenses) would allow the left and right images to be placed on one piece of film, but side-by-side. You would still have to have external polarizers. The optics are expensive, and the image is dimmer, but it eliminates the hassle of keeping two projectors in perfect sync. Copyright 1989 Greg Wageman DOMAIN: greg@sj.ate.slb.com Schlumberger Technologies UUCP: {uunet,decwrl,amdahl}!sjsca4!greg San Jose, CA 95110-1397 BIX: gwage CIS: 74016,352 GEnie: G.WAGEMAN Permission granted for not-for-profit reproduction only.
ray@hydroplane.cis.ohio-state.edu (william c ray) (10/10/89)
someone writes (in regard to using amorphic lenses for 3d polarized projection instead of synched projectors) The optics are expensive, and the image is dimmer, but it eliminates the hassle of keeping two projectors in perfect sync. Whats so hard about syncing projectors? link them MECHANICALLY... either drive them from the same motor, or link the film transport system... (I've already done this with some super8 stuff... My question is, how do I place the polarizers for maximum effect, and are there sources of polarizers that do a better job than the standard photographic variety. I've had very poor luck getting good separation... do I need a special screen, polarizers on both lightsource and lens, or what?) Will Ray
pvo3366@sapphire.OCE.ORST.EDU (Paul O'Neill) (10/10/89)
In article <65904@tut.cis.ohio-state.edu> william c ray <ray@cis.ohio-state.edu> writes: >how do I place the polarizers for maximum effect, .............. >I've had very poor luck getting good separation... do I need a special >screen, ................. , or what?) > Yes, you need a "special" screen. The old "silver-screen" type will preserve the incoming polorization. Newer "glass-bead" type screens scatter the incoming polarization and are useless. Paul O'Neill pvo@oce.orst.edu Coastal Imaging Lab OSU--Oceanography Corvallis, OR 97331 503-754-3251
lmeyer@well.UUCP (lhary meyer) (10/10/89)
The 3D films have two windows in each frame, the top half is left and the bottom is right ( or v-v, no standard exists). Via a assemblage of prisms and mirrors, each windows light follows a separate optical path to the screen. You put sheet polarizers at +/- 45 degs. (not Hor. and Vert), one per path. Thus two simultaneous images are projected upon the same screen, but with ortag (sic) orthagonal polorization. You could also use two separate projectors, as proposed above, but the problems of holding perfect frame sync and shutter phasing are very tricky. When done properly, as at Disneyland with dual 70 mm, its works great!!
flip@pixar.uucp (Flip Phillips) (10/11/89)
In article <65539@tut.cis.ohio-state.edu> william c ray <ray@cis.ohio-state.edu> writes:
:Well, I may just be an idiot, and someone may have some magical way of doing
:2 polarized images overlaid on the same piece of film, (and Pixars may drop
:to $15 tomorrow...) But if I were to do a polarized 3d film, and I'm only a
:punky undergrad, with no experience here, I would project *2* simultaneous
:strips usicross polarized polarizers, one on each projector, but what
:would I know?
:
:Will Ray
Well, yep, thats right. (Not the $15 pixar thing... but the polarizing
stuff)
The films were calculated with one strip for each eye, two projectors were
synchronized together, and a polarizing filter was placed on each projector.
This presented an 'encoded' picture of horizontal and vertical polarized
light on the screen, and your glasses 'decoded' it. Simple...
Seems a silver screen is necessary also, my guess would be due to the
light scattering non-uniformily on a white screen, thus throwing the
polarization off.
There are also under/over doohickies where you print the right and
left images, half size in the vertical dimention, on the same frame
of film. Then, a special lens with a splitter reads each seperate image,
polarizes it and projects it. Saves you from having to have two synched
projectors but then you only have a half sized image... tradeoffs, tradeoffs.
Flip Phillips {sun | ucbvax}!pixar!flip
Pixar - Marin County, Californialmeyer@well.UUCP (lhary meyer) (10/11/89)
Yes you MUST use a silvered screen!!! A high gain screenfor a video projector often works well. Put one polorizer on a flashlite and observe the beam from the screen thru another polorizer. You should get excellent extinction if the scrren is OK. Also angle alignment is critical to about 1 deg.
spencer@heinlein.osc.edu (Stephen N. Spencer) (10/11/89)
[reply to spencer@heinlein.cgrg.ohio-state.edu, not what's in the header...] In article <7176@pixar.UUCP> flip@pixar.uucp (Flip Phillips) writes: > >There are also under/over doohickies where you print the right and >left images, half size in the vertical dimention, on the same frame >of film. Then, a special lens with a splitter reads each seperate image, >polarizes it and projects it. Saves you from having to have two synched >projectors but then you only have a half sized image... tradeoffs, tradeoffs. > You're right. The over/under stereo prints WERE half-frame images, horizontally oriented. The "lens" actually has several lenses which corrected for the format disparity. They were a b*tch to focus (and where I worked, a b*tch to install -- I seem to remember that the lens was longer than even a CinemaScope lens and we had to do a little re-construction of the area around the opening in the wall of the projection booth where the image would come out...) _Friday the 13th Part 3 (in 3D)_ was done this way. I don't remember (or don't know) the format of _Comin' At Ya!_ (another forgettable 3D movie which was out around 1981-1982) but I remember that the screen was painted silver for this feature. The one effect I remember (sorta sticks in my mind...) is a flaming spear thrown "at the camera." -=- Stephen N. Spencer |"For a successful technology, reality must take ACCAD, 1224 Kinnear Rd. | precedence over public relations, for Nature Columbus OH 43212 | cannot be fooled." - Richard P. Feynman spencer@heinlein.cgrg.ohio-state.edu OR spencer@cis.ohio-state.edu
pearce%alias@csri.utoronto.ca (Andrew Pearce) (10/11/89)
In article <65539@tut.cis.ohio-state.edu> william c ray <ray@cis.ohio-state.edu> writes: |Well, I may just be an idiot, and someone may have some magical way of doing |2 polarized images overlaid on the same piece of film, (and Pixars may drop |to $15 tomorrow...) But if I were to do a polarized 3d film, and I'm only a |punky undergrad, with no experience here, I would project *2* simultaneous |strips usicross polarized polarizers, one on each projector,... | Will Ray Well, no, I wouldn't do this. Does the projectionist really have to worry about two reels of film and about threading them through the projectors so they start at the IDENTICAL frame each time the films are spooled up? Not to mention the problems with aligning the projectors on the screen. I thought of this method but dismissed it as too stupid, we live in an age of wonders and technology, don't we?
jim@mickey.UUCP (jim houston) (10/16/89)
In article <475@alias.UUCP>, pearce@alias.UUCP (Andrew Pearce) writes: > > My question is, what are the actual mechanics of placing the two images on > film? Is the film double exposed, once for each image of the stereo pair, > with different polarization each exposure? Does the film grain retain this > polarization? Or is it a special type of film with a polarized emultion on > each side? > The separation is achieved in the projection of the film, not in the recording of the image. In the simplest method, two cameras are used to create two strips of film; one for the left eye and one for the right. Each strip is developed normally and a print is made. The prints are projected onto an aluminized screen using a pair of inter-locked projectors containing different polarizing filters Other methods have been used however. The trick is placing the stereo pair on the film in a layout that matches the projection system that will be used. As an example, over-under pairs can be used. In this format, both "eyes" are recorded on the same strip of film. One frame of 35mm film will contain the right eye in the top half of the frame and the left eye in the bottom half. A special lens is then used on the projector to overlay the images on the screen. Other formats can be used as well. The images can be placed on the film as two squeezed (i.e. anamorphic) images on the left and right half - again requiring a special lens to properly split and project the image. I don't know exactly which format was used at SIGGRAPH for the 3D films. Jim Houston Walt Disney Pictures