I have been in a booth and saw the screen of two of the new digital IMAX installs in so cal. It is a pair of DLP projectors side by side. On rails so they can spread them for service. They are inside a large metal housing with IMAX stamped all over them, but when you lookin the vents, you can easilly tell they are Christie projectors inside. There is no camera I could see, and no servos on the lens centering that I could spot. Accoriding to the people closly gaurding the secrets, they are hyper accurately overlaid exactly 1/2 pixel off both vertically and horizontally to totally cover the pixel grid and the special IMAX processor is taking a full 4096 x 2160 feed and feeding the two projectors the alternating pixel data. Of course for 3D they do run left eye / right eye with linear polarizers in front of the projectors. They have a cute robot arm with 3 positions, open for 2D, closed to douse between shows, and polarized for 3D. They use the douser infront of the projector for one big reason, thermal settling. They have to align the projectors when they are fully warmed up, and the internal douser allows the light engine to cool. They also want a hard douse to make the black screen totally dark between shows, electronic black is not that dark.
When I was in there, they were running "Eagle Eye" which was also running just a few doors down in 2K DLP and across the hall in 35 mm film. They were selling about 2 to 1 on tickets for the IMAX vs film, and the DLP was right between. Funny thing is they charge more for the IMAX, but the same for film and 2K DLP. Yes, more people paid extra for the IMAX. When they converted the room from 35 mm to IMAx, they only lost a couple extreme front corner seats due to the curve of the screen. It is perforated with the spekers behind. But this was odd to me. It is just 5.1 channel. The rack has just 4 stereo amps in the booth. One channel each used for left, center, right, l surr, r surr, and two channels for the sub array. The 8th amp channel is running the booth monitor speaker. Yup, passive x-over, not bi-amped. The amps are each rated at 2000 watts into 4 ohms per channel, so it is not meak, but I have set up many ordinary theatres with far more power for the size room. In fact the 35 mm film system that was removed from this very room was more powerful. And of course in IMAX tradition, they just stuck one huge speaker in each rear corner for the surrounds. They even left the string of JBL 8340A's from the film system, but no longer connected to anything.
Looking at the picture, it looked okay. First complaint... No masking. The screen is sized to match the 2048x1080 aspect ratio. True IMAX releases are supposedly going to use the whole chip for this wider 1.9 ratio. Flat 1.85 movies have side borders and scope films will have top bottom borders. It was BRIGHT, I would guess close to 20 fl on peak white, judging from the picture in the 2K DLP house which I know is set for the DCI 14 fl. The blacks looked good, but nothing shockingly dark, but overall, it was tough to compare the two directly because the IMAX looked like a CRT tube set with the contrast cranked way too high. Once my eyes adjusted to the high brighteness, it looked okay, but going into the 2K DLP house just looked like more detail in the dark areas to me. The film house was not a fair comparison, it was obviously a bit dim, I would say less than 12 fl open gate and the picture was not dead steady. Of the 3 my first choice would have been the 2K DLP. It just was the most pleasing to walk in and watch. The IMAX was more in your face.
As for sound, the 35 film house sounded best that day. This is odd being that Dolby Digital on film is only 348 kbps total for 5.1 audio. But that room was recently tuned up and sounded great. The 2K house sounded good, but I think the balance was a tick off and sounded too bright. The IMAX sounded okay, and was running at the right level, the theatre had the other houses a bit below spec, but the IMAX has no normal fader, it is locked so only the approved operator can touch it. The surrounds were hotter, but point source, and the sub seemed over boosted. Not bad, but just not as smooth and natural as the others. The IMAX and the 2K DLP should both be uncompressed 24 48 PCM. This is a very well maintained theatre, and going into any one of the houses was a very good, far beter than average movie going experience. With the larger screen, hot sound level, and bright picture, I am sure the average movie go'er feels they are getting something extra for the slight increase in ticket price. And the 3D with dual projectors should be a big plus. "Eagle Eye" was not a good judge of image resolution. I will say though that I was far less aware of the pixel grid when I was at the front of the stadium seats. I can't say if it was truely sharper, or if the offset just hid it better though. I will try to critique it a bit better if and when I get behind the scenes there again. All in all, it is a good picture and good sound, but it is certainly not a replacement for 15/70.