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Comment by Animats | Hacker News Reader

Well, of course it has to block most of the room lighting. They can't draw dark. The display has to be brighter than the ambient light. I'm surprised these things don't have an auto dimming shutter, like a welding mask, to adjust how much outside light gets through.

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Well actually you can, it's called an LCD

Well, there is this rear view mirror in cars which essentially draws dark by blocking out the area where the sun would reflect into your eye.

Expanding on that, maybe with some kind of holographic shenanigans, we can have something that not exactly draws dark, but occludes light very cleverly.

Like an LCD of some sorts.

Exactly my point. :)

The update rate has to be very high and the alignment perfect or it will drive users nuts. Which means it will probably be done soon, although not in this round. Doing it with lightweight short path optics is also difficult. All this stuff with diffraction gratings and Fresnel lenses makes for a crappy image. That can sometimes be overcome; the Polaroid SX-70 camera had a very compressed optical system with Fresnel lenses without compromising image quality too much.[1]

The other option is simply to show the real world via a camera feeding into the system. That's been tried many times, and it works OK, although lag will make users faceplant or ill.

[1] https://www.technologizer.com/2011/06/08/polaroid/sx70-light...

OMG I so much want an SX-70. I will make it happen sooner or later now that there is film yet again for it.

The problem is focal conjugates; you can't darken something close to the eye and have it look like a dark region at a distance without focus blurring ruining the effect.

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