Optical DIY Eyepiece HUD: Plausibility, Materials, and Possibilities

[jgeating]

I'm am looking at the plausibility to make/hack an eyepiece HUD out of a reflective piece of curved glass/plastic, a camera, and a viewfinder/mini-screen.

It would be nice for it to all mount to either a modest sized helmet or a tight head strap. I remember having an old '90s video game that you would tie around your head with the LCD screen facing down, and there was a piece of plastic that would reflect the screen into your eye. I would like to mimic something similar, where a viewfinder or other small, lightweight screen is reflected into my one eye, but both eyes can still see my surroundings. Once calibrated with a camera, for example, I could do any sort of computer vision and display it on the HUD.

With this base, the possibilities are endless, ranging from avionics (e.g. add some gyros, accels for orienting the HUD) to paintball/airsoft (gps mapping).

Does anyone have any experience in relation to a good material for the reflective piece, any ideas about what viewfinder to use. Also, if this is even plausible in terms of optics and the nature of human vision. I think it would be awesome to eventually use this to control an aeroquad realtime while on the move.

 

[Unrest]

One issue would be keeping the brightness of the image comparable with the real world. Perhaps it would need a light sensor to adjust either the screen's brightness or the transparency of the reflector (like an auto-darkening welding helmet). I suspect having a darkening reflector may be needed to keep the backlight's brightness realistic.

For selecting a screen, I'd start with some optics diagrams and calculations to determine how big it should be with practical lenses to make it appear at infinity. It might also need to be focusable for use at close range if you don't want to refocus your eyes to read it.

Also work out the required brightness (measured in nits) so it can compete with the sunlit scenery. There's a whole painful world of light calculations you can use to work this out.

 

[jgeating]

Thanks for the insightful response. I'm not quite as worried about the brightness as much as I'm worried about the focusing. For brightness, I think I might use a light dependent resistor, possibly with shields so it only accepts light from frontwards.

Can you expound a little more on the focusing. Ideally, I would like for this to seamlessly overlay the user's vision, and always remain in focus.

 

[Unrest]

Thanks for the insightful response. I'm not quite as worried about the brightness

It could certainly be an issue. You can't easily read a computer screen outside. So you would need something emitting more light than that and condensend into a smaller area to fit on your head. Or just dark glasses.

Can you expound a little more on the focusing. Ideally, I would like for this to seamlessly overlay the user's vision, and always remain in focus.

That's asking the impossible, unless you can detect the distance the user is focussing on. For outdoors you can probably assume they're look at infinity or pretty close, and put the image at the hyperfocal distance based on the eye's and screen's resolutions.

I don't know how the lenses would actually work. I guess you can draw ray diagrams to get a feel for it. Ignore the reflecting sheet at first because it won't affect the distances, just change direction.