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This topic comprises 2 pages: 1 2
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Topic: Sony SRX-R800 phosphor laser projector
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-07-2017 02:06 PM
Well, I tend follow Mark on this, unless I'm missing something here:
A light source with a smaller etendue should increase the efficiency of the light source, since there's less light getting lost in reflectors, lenses and other optics trying to focus the light on the DMD/LCoS imager. Yet, a more efficient light source alone doesn't imply a higher contrast in the image.
Besides the quality of both the lenses and the prisms, the contrast is primarily going to be defined by the quality of the imagers, the DMD or LCoS type devices. More precisely by the difference between the amount of light they're able to reflect towards the screen and deflect away from hitting the screen. A 100% perfect system should be able to control this per pixel and should reflect 100% of all the light in an on-status versus 0% of all the light directed at it in an off-status.
One thing where I think laser could help is, because the laser light in itself is more coherent, there will be less "non-directional" or "stray" light hitting the imager at an odd angle and causing leakage into the image at large. Although I'm pretty sure this effect exists to some extend, I have no real idea how much it affects current designs. There might also be other solutions for this than lasers, like polarizers. Obviously those will not enhance the efficiency of the light sources.
Another thing could be the lenses and prisms themselves, but this only applies for 3P/6P laser systems. The monochromatic aspect of the primaries will probably make it easier to correct for chromatic aberration, since you only have to account for three very discrete wavelenghts. This however, should increase the sharpness of the image, not so much the contrast.
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Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
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posted 11-08-2017 06:36 AM
LCD projectors do use prisms as well.
You can always increase contrast easily by sacrificing light. But who wants to do that, other than for screening rooms/post production or simulators?
There are other ways to recombine light, but prisms do not only have disadvantages, they also have a great advantage - stability, once built, there is no drift in registration. The Laser IMAX solution is very expensive in order to reduce that issue. And the Kodak/IMAX patents may prevent other companies from doing it commercially.
There are some references that the maximum achievable on/off contrast for current DLP imagers is around 10.000 to 12:000:1. While Laser IMAX comes close, other manufacturers slowly seem to achieve something in the 3000-5000:1 ballpark with their LIPs. Sony quotes a very solid 8000:1 for their UHP SRX-R 5xx series. I guess it wasn't that complicated to improve this towards the 10.000:1 they now quote for their phosphor laser - even their (non cinema) SRX-T615 UHP counterpart is quoted with 12.000:1. Dolby Vision/Cinema is a bit different as it not only cares about sequential contrast improvement with it's (expensive) 'local dimming' approach.
With exit/emergency lights, auditorium design and patrons clothes and faces bouncing light back to the screen, I guess it doesn't make sense to achieve much more than 5000-8000:1 on the projectors part. How that translates to in-picture/ANSI contrast for the different technologies is an interesting question. Usually, more work is spent on analyzing high end home cinema projectors than in evaluating DCI machines. The Barco LHC machines seem to target these realistic numbers. Barco started to quote sequential and ANSI contrast figures for their RGB laser machines. From these numbers, the LHC machines look very promising. I hope they also improve on the speckle issue.
At some point, self illuminating screens will take care of that issue as well, and also improve in-picture/ANSI contrast greatly.
- Carsten
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