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This topic comprises 2 pages: 1 2
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Author
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Topic: Sony SRX-R800 phosphor laser projector
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Tom Bert
Expert Film Handler
Posts: 134
From: Belgium
Registered: Apr 2010
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posted 11-08-2017 08:31 AM
quote: Marcel Birgelen
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.
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quote: Marcel Birgelen
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.
You're mixing up things here:
- "coherence" in the context of laser is something else, it's not spatial coherence
- what you call coherence here is actually the same thing as étendue: a low étendue/high-F-number system helps to boost contrast.
On this topic:
quote: Mark Gulbrandsen
Someone needs to step up to the plate and get rid of all the glass, meaning the Prism itself. It can't be THAT difficult, except getting around the Imax patents. Hey, others have done THAT over the years. LCD projectors have never used big prisms in them that I have ever encountered and they do their tricks with just high temperature plastic frames.
Using a prism reduces size, complexity and cost: there are good reasons to do so.
Many LCD projectors are single chip: different world than 3-chip, which is the only way to achieve image quality that cinema expects/deserves.
3-chip LCD projectors >20klm... I don't know any to be true. Heat management (linked to reliability) is a complex and important matter.
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-08-2017 03:53 PM
quote: Tom Bert
You're mixing up things here:
- "coherence" in the context of laser is something else, it's not spatial coherence
- what you call coherence here is actually the same thing as étendue: a low étendue/high-F-number system helps to boost contrast.
I do know that "coherence" isn't the right word here, hence the quotes.
I do understand why a "High-F-number" (I'll remember that one ![[Smile]](smile.gif) ) light source will be more efficient in terms of energy you put in v.s. the amount of light you get out of it (for the purpose of projection), but maybe you can explain why a "High-F-number" system eventually will improve the contrast of the image.
Is it because a "high-f-number" light source will cause less unwanted reflections inside the light path at large or are there other reasons for this?
quote: Tom Bert
Many LCD projectors are single chip: different world than 3-chip, which is the only way to achieve image quality that cinema expects/deserves.
I guess the biggest market for LCD projectors right now are 3LCD projectors and they do have three chips and either a mirror or prism assembly.
But even the biggest player in the 3LCD market, Epson, doesn't seem to be capable of building high-lumen projectors based on LCD technology and their phosphor laser projectors are also based on reflective panels similar to LCoS.
quote: Mark Gulbrandsen
All 3-LCD projetors I have repaired, mostly Panasonic, all have integral light engines in a single plastic frame. The dichro filters, the LCD's themselves, and extra heat and trimming mirrors are all in that frame. Not that I am advocating using plastic in a DLP... But all I am saying is they never had a prism to start out with.
Why not go old-school and have three separate light paths like the CRT projectors did? They were so bulky, nobody even tried to combine the output of the three tubes back to one beam. Also, I somehow miss the old days of converging and edge-blending those things together for the better part of the day. ![[Wink]](wink.gif)
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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 05:12 PM
https://www.barco.com/en/News/Post/2013/6/26/Why-laser-is-just-another-part-of-the-image-quality-puzzle---part-two
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In this installment, we’ll take a look at how étendue is impacting image quality. In addition, we’ll see how laser technology has a direct impact on the way light is transmitted, thus creating better contrast and uniformity.
Étendue
Étendue describes how big or compact a light source or bundle of light is. It is a combination of the surface and the angle at which light is emitted. The most specific thing about étendue (also the biggest challenge for optical designers) is that étendue can only grow. Applying this to our case above where we were thinking of combining multiple lamps to achieve a higher light input, we are confronted with the –relatively huge étendue of lamps: the arc where the light is formed is several mm long; furthermore the light is emitted in all possible angles. Combining more lamps only makes the system étendue even bigger. So if you want to make use of all this light, you will have to dimension your projector accordingly: a big light path, bigger chips, bigger angles, ... all too expensive. The nice thing about a laser light source is that the étendue is tiny: the surface of one beam is micrometer scale and thanks to the collimation the angular distribution is almost zero. This makes it easier to stack and scale lasers and accumulate a huge (but still low étendue) light source. Net result: the possibility of higher brightness, and better image quality!
Stray light
Lasers are not only about more raw power and pumping more light into the projector light engine; the higher collimation (i.e. a lower étendue, our word of the day) also has a direct positive effect on efficiently transporting light and an indirect contribution to better contrast and uniformity. In any projection system you want to control the light flowing through the system as tightly as possible: light bouncing off surfaces and going places where you don't want it, never has a positive impact on the image you are trying to project. Looking at digital cinema, the image-generating component (the chip) always has a certain light acceptance angle: any light in the system outside that cone is stray light. Stray light is out of your control and exits the lens on top of to the actual image you are trying to create. Added to a very bright image, the impact will be small. Added to dark scenes, it will ruin your contrast ratio. Existing cinema set-ups operate at a contrast of around 2000:1. The geometry of the lamp light distribution plays an important limiting role here. When taken into account in the system design, laser light sources and their more collimated nature can boost contrast ratio. Do note that other components (such as the chip) are still impacting and an infinite contrast ratio will never be possible.
The power of uniformity
Another important part of the image quality puzzle is uniformity. Whereas brightness and contrast ratio are local parameters (measured in one location on the screen, sometimes averaged out); uniformity is a global parameter. It quantifies how well the image quality is maintained across the entire screen, from center to edges. A good uniformity is achieved (among other things) by illuminating the surface of the imaging chip with a nicely filled and rectangular-shaped bundle of light. As mentioned above, the angles of this light cone affect the contrast ratio; the shape and fill of the cone impact uniformity. In the case of lamp-illuminated projectors, at the very start of the light emission, we start from an ‛arc-shaped’ source of light: between the anode and cathode of the lamp, a small 'bridge of light' is where the actual light generation happens. To achieve perfect uniformity, the optical components between the lamp and imaging chip (reflector, light rod, ...) have to reshape this arc (long, thin) into the rectangular shape of the chip. If you are not willing to compromise the size (and cost) of the set-up, this is a very hard thing to do. That is why the current cinema DCI spec for uniformity takes realistic values around 80%. This is where the laser comes in. Light generation no longer starts from an arc between two electrodes, but as a stable collimated bundle out of an aperture. This makes the life of the optical designer easier: by opening up the bundle (uncollimating) or adding up several bundles (here our good friend étendue again) it is possible to fill that rectangular aperture that the imaging chip is built for. The net result is not only a better uniformity and better image quality; but ‒ once again ‒ a more efficient light use since you don't have to start applying compensation tricks for inherent lamp non-uniformity. Do note that ‒ just like in the case of contrast ratio ‒ other parameters, like the lens, also impact the on-screen uniformity. Even parameters outside of the projector’s control, like screen gain, impact the perceived uniformity. So yes, laser can positively impact uniformity; but it will not magically lead to 100% perfect uniformity. This is true of any laser-illuminated projector.
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- Carsten
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Marcel Birgelen
Film God
Posts: 3357
From: Maastricht, Limburg, Netherlands
Registered: Feb 2012
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posted 11-13-2017 03:46 PM
I've heard them using a "stepped light engine" approach. I didn't read the whole patent and I've encountered it before. Someone referred to it as a possible scenario how the "Dolby Vision" HDR stuff works on the AVS Forum. But it describes a zonal system using white light with a "zonal modulator" that regulates the luminosity per zone. But I guess the Dolby Vision system doesn't combine the color primaries first, only to split them again afterward?
So, in this case, they're using a modulator per color, so that would either be three extra DMDs or LCoS like devices.
I was wondering if you could not develop a more elegant zonal system using laser sources. Since you've got a whole bunch of "high-F-number" sources at your disposal, isn't it possible to bundle them in an orderly fashion where every module represents a zone? It's one of the fancy aspects of lasers that you can modulate them at GHz speeds if you require to do so.
quote: Tom Bert
The big con is light efficiency (lm/W): e.g. a 5% system in series with a 5% system yields 0,25% net efficiency. I've heard stories of the Dolby Cinema system consuming >20kW electrical power
If it acts as a pure serial system, then (5/100)^2 * 100 = 0.25%... you're right, it would have a net efficiency of just 0.25%. But I doubt it's really that horrible, isn't it? Because can you really "serialize" the losses in an integrated system like this?
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