How can a DCI Projector have a dead pixel?

[Marcel Birgelen]

Apparently implementation and intent are pretty far apart. Barco advised we only use the "dowser" within a black, to avoid a bunch of visible weirdness on screen as the DMD mirrors move out of their storage position. So not as "immediate" as one would hope.

Just some small timing issues. Software developers call those things race conditions.

But yeah, eliminating the physical dowser was a cost-optimization measure, much like eliminating masking around a screen...

[Christos Gartaganis]

The elimination of side masking is one of the worst things that ever occurred when digital projectors became the norm in most theaters around the world. It compromised the quality of the overall cinema experience, especially while watching a 1,85 aspect ratio feature with visible vertical black bars appearing on both sides of the projected image, especially during low key atmospheric scenes. From a cost perspective this is a very unwise choice considering the high price tag of current laser 4K cinema projectors.

[Marco Giustini]

I've been thinking about how something like a laser-pointer could damage three DMDs and I'm pretty sure that any "street legal" laser won't do this. But a professional laser show using a powerful RGB/white laser easily exceeds 500mW often going up to 30W or more for indoor use and even more for outdoor, which could certainly fry one or more pixels on three DMDs at the same time if it hits from the outside.

Well it was a small venue in a village, if it was laser damage it was something small and portable. I was told that it takes very little for the DMDs to get damaged. The lamp light is spread over the DMD, a laser coming from outside would be apparently focussed on the DMD.

There was a clear damage to 2-3 pixels on all colours, I'll see if I can find the photos I took.

[Marcel Birgelen]

Well, I googled a bit around and apparently, everybody can nowadays buy 500mW+ laser pointers right from AliExpress... Those laser pointers used to be like 50mW max, but at those intensities, stuff is becoming increasingly idiotic... you can probably burn somebody's retina at a mile or more distance with such a laser pointer...

[Hong Sung Hyeok]

Please also refer to this.
https://www.barco.com/en/support/kno...xternal-lasers

[Marcel Birgelen]

Yeah, that looks pretty "fried". Still, what strikes me is that the damage seems to be almost solely to the mirror part, there is almost no visible damage to the back of the DLP chip. Maybe it all went so fast that all energy was absorbed by the mirror, before it could hit the substrate. Maybe, the mirrors also are a potential target, because they have so little mass?

[Marco Giustini]

I'm not an optical engineer but I'd imagine there is where the light focus - hence where it has the maximum energy?

[Marcel Birgelen]

Yeah, sure, the heat will be concentrated to a very small point source. Due to the small intrinsic mass and no hard connection to any backing material, a single mirror cannot take much heat and that's why it is extra vulnerable. At least, that's my theory. The backing substate layers are still connected together and thus can act more as a heat-sink, most likely avoiding much of the damage that way, if it gets hit.

Still, those mirrors are exposed to quite a bit of heat during normal usage too, it still somewhat blows my mind how a single stray laser beam will fry away the entire mirror, while the same mirror can withstand years and years and years of battering of a 6 kW light source, obviously largely defused... but still.

[Marco Giustini]

oh yes, it also feels weird that the DMD can take a 7000W xenon lamp but it literally melts with a portable laser pointer!

[Fraser Falconer]

An analogy would be like a magnifying glass on a piece of paper in the sun