Hector Martin

I'm assuming it's probably just a polarizing sheet, similar to the material used in sunglasses. I don't think that would be hard to get, it's the DLP that would be more of a challenge.

Why would it be a polarizer? What purpose would that serve? I figured it would just be some translucent film (e.g. the kind of stuff used for rear projection). But yeah, easy to source something that will work. The DLP is the issue. Though it can't be that hard to reverse...

I'm most intrigued by how noisy it will be... I'd expect that persistence of vision like this will require a fairly high (>60Hz) refresh rate, especially given that this can't rely on phosphor emitting light after the break has moved on...

That's a big excursion for what is effectively a large diaphragm...

I'd agree that the projection surface will want to take as much of the energy as possible, to give good contrast, while showing the top surface to light... so "fuzzy" / frosted plastic?...

Keeping it flat will probably be a challenge, which will be required for distortion-free projection - adding mass to the surface.

And I'm not convinced by DLP... If it was located in the centre at the bottom of the unit, you'd probably get a cone of usable protection volume... Laser(s) are required to maintain focus, so possibly a galvanometer / piezo actuator... but still... "cone"... hmm...

maybe a source off to the side, with a top/bottom pairing to cover the full travel of the surface? Bit yucky...