I saw INTO THE DEEP in New Orleans in 1996 and L5 (a Japanese funded space adventure) in Vancouver in 1998 and they both had the excessive horizontal parallax, high ghosting (crosstalk in which right eye sees some of left eye image and v.v.), some vertical parallax, jump cuts from large to small parallax or v.v., asymmetrical illumination etc. I also saw the 3D IMAX computer generated ride film RACE TO ATLANTIS in Las Vegas which had most of the same problems, with the addition of excessive movements of the seats. The result of all these binocular asymmetries, ghosting, excessive parallax etc. is stress to the optic cortex and elsewhere in the brain, which is usually called eyestrain.
Originally these films were projected with crossed polarizers and passive polarized plastic glasses, like most 3D films have been. Starting in 1990, at Expo 90 in Osaka, Japan, IMAX began using LCD shutter glasses for field sequential 3D display, a technique that has become common for 3D video and computer graphics. This seems to be IMAX's method of choice for the many 3D theaters they are constructing and was the one used here. The original LCD shutter glasses were quite bulky and IMAX has improved them, adding integral stereo speakers and a button that gives the user the choice of Japanese or English. Unfortunately, the headsets are still too heavy and worst of all the LCD's are too far from the face so one can see the edges of the lenses, detracting from the experience considerably and defeating the point of having seats close to a very large screen. Even the cheap glasses used in some of the consumer LCD shutter glasses systems are able to avoid this problem.
The worst problem with the IMAX experience however is the incessant overuse of large values of negative parallax. They seem to converge for all shots in all films (with possible exception of some of the computer graphics scenes) at about 100M(300 feet) so that all objects, except the most distant, have negative parallax and appear in screen space with the nearest objects having from a few cm to two meters of parallax, depending on the shot. With the most distant seats being only about 25M(75 feet) from the screen this means that the eyes are nearly always crossed (converged) in audience space and sometimes just a few meters from the viewers. Even from the back seats (where I strongly recommend viewers sit) this is hard to take and I pity those who sit in front.
Another problem is IMAX's failure to grasp the concept of the stereo window (or refusal to accept it as a sensible idea). When stereo images are displayed, one has the choice of using horizontal shift of the images and masking of the right and left vertical edges to create the correct window. In this case the right eye sees more out of the left side of the window (movie screen) than the left eye and v.v. This creates a natural looking image in which objects with zero parallax appear approximately in the plane of the window, just as they would when looking out a window in the real world. IMAX, however, gives the entire film a negative parallax so that the entire image is projecting out into the theater. In this case the right eye sees less of the image at the left of the screen than the left eye. This makes the image look odd and is very disturbing if one looks away from the center of the screen. Only in some of the graphics shots or in those reproduced from old stereocards does the window approach correct framing. I have been told that their animated short PAINT MISBEHAVIN has a correct stereo window.
In addition , there is often the excessively rapid panning and camera movement and jumping between large and small parallax values that make it difficult or impossible to fuse the stereo image. These problems are not unique to IMAX however, and are nearly universal in 2D and 3D films.
Another problem which I have also noticed in other double strip 3D films, such as the Muppets movie at Disney World, is an asymmetrical illumination flicker of perhaps 0.5 or 1 Hertz which varies from one part of the frame to another and is most noticeable in brighter shots. Perhaps this is due to varying print density in the negatives or prints, shutter variations in the projectors or cameras or optical printers, or even variations in the LCD shutters, or a combination of them all. It is noticeable in either eye but is more striking binocularly.
Now to the films themselves. All the IMAX films are directed an audience of ten year olds (or less). This is understandable but most regrettable. This is the major reason why, in spite of my being a 3D maniac, I have had little interest in a second viewing of any IMAX film. Though the acting, directing, writing and camerawork have improved somewhat, there is virtually nothing in any of the films, 2D or 3D, to appeal to the intellect, heart or spirit of an adult. In fact I think most older kids are bored much of the time and even incredulous at the often silly plots. The two 8 year old Japanese-American kids who sat next to me during T. REX were talking and squirming much of the time and made several disparaging comments about the plot - "a forest outside the bathroom!", etc. T. REX has some very nice computer generated dinosaurs, but the absurd and insipid plot and dialog wastes much time on shots of a young lady whose mind has slipped back in time where she hallucinates dinos.
WING OF COURAGE is another largely boring tale of a pilot lost in the Andes mountains in the 1930's. They hired some mainstream actors such as Tom Hulce and Val Kilmer but there was just no opportunity to express their talents. SEIGFRIED AND ROY: THE MAGIC BOX is entirely devoted to the Las Vegas magicians famous for their use of animals such as white tigers. If you like this kind of act you will see them here better and far cheaper than you could in Nevada and I assume much of what they did in this film will never be done live. Perhaps the only IMAX 3D film that does not give you time to get bored!
The film originally made for Sony's theater in New York--ACROSS THE SEA OF TIME -- gives you plenty of time to get bored. It tells the story of a young immigrant around 1900 with old stereocards which IMAX first did in a 1986 film. These mostly have an almost correct stereo window and reasonable parallax. Much of the film is wasted with dull shots and weak dialog.
Finally there is ENCOUNTER IN THE THIRD DIMENSION--hands down the best thing IMAX has done. Again there's some insipid dialog, but intensive use of computer graphics, well blended with live action, keeps it interesting. Its major theme is to tell the story of 3D movies and photography. Though there are a few brief clips from 3D films, they are not identified. The review of 3D imaging is feeble--inexcusable given IMAX's resources and the vast amount of easily accessible material. Instead, they throw in a lot of very loosely connected computer graphics. Great visuals but a C minus on story.
So, the bottom line is that we still have to wait for the day IMAX learns how to do 3D and decides to make a film for grownups. Like so many large entities, IMAX seems immune to criticism (I have been telling their staff about these problems for 15 years, and I'm not the only one.) so perhaps only a class action suit by annoyed customers will get any response.
I submitted the above article to IMAX and one of its subsidiaries. The subsidiary said they had no idea what to say. Liam Romalis of IMAX replied as follows:
"Your article is fine to publish with one correction: Encounters in the Third Dimension is NOT an IMAX film, or a film produced by Imax Corporation. Rather, it is a large-format film produced by nWave Productions."
Considering the numerous and devastating criticisms above this reply is astonishing!
Another serious problem that arises when the parallax is large is the breakdown of the focus(accommodation)/convergence lock of the eyes. Normally, the eyes are always focused and converged on the same plane, which in imaging systems is usually the screen. In stereoscopic displays however, though the eyes will still try to focus on the screen, they will try to converge at the point in space which permits fusion of the stereo object of interest.
It is to be expected that, as the parallax gets larger, the visual system might try too converge on the screen(minimizing the depth), or to focus on the point of convergence(blurring the image) and perhaps to range back and forth between these extremes.
Such effects have been observed, most recently by Ms. Amelianova at NIKFI in Moscow, who did experiments in a stereo cinema and reported them in Russian and at the 1992 Tokyo Seiken Symposium on 3D Imaging.
In real world scenes it may be hard to separate such effects from the different focus of objects due to the camera lenses. However in the recent IMAX film Cyberworld in 3D, all images are computer generated and printed directly on the film and in perfect focus.
I saw this film projected at Sony's Metreon in San Francisco and at the Krung Thep IMAX in Bangkok and objects were often blurred and/or the depth was muted due to the excessive parallax(and rapid cutting from large to small parallax or vv.). This was in spite of the fact that, as always, I sat in the last row of seats to minimize the problems. IMAX's superb imaging system is a unique opportunity to detect mistakes or imperfections in stereoscopic technique.