Head Up Display

[unlimitedbacon]

My question is about the Head Up Displays we are all too familiar with. I'd like to know how the optics work in real life HUDs. I understand that the image you see is a reflection from an LCD or CRT. The cool part about real HUDs, though, thats not obvious from 2D pictures is that the image appears very large and very far away. This is so you don't have to refocus your eyes from the object you are looking at to the virtual display. Its an amazing effect if you've ever seen it in real life. But if you get a piece of glass and look at the reflection of you're monitor, it only appears to be inches in front of you, not hundreds of feet. I can't find anything on the internet that explains how this works in a practical sense. I've read that the light needs to be "collimated" and I sort of understand what that means, but how do you do that? What kind of lenses do you need? Whats the math involved? The reason I'm asking is because I might be interesting in building one, just for fun.

 

[Hielor]

My question is about the Head Up Displays we are all too familiar with. I'd like to know how the optics work in real life HUDs. I understand that the image you see is a reflection from an LCD or CRT. The cool part about real HUDs, though, thats not obvious from 2D pictures is that the image appears very large and very far away. This is so you don't have to refocus your eyes from the object you are looking at to the virtual display. Its an amazing effect if you've ever seen it in real life. But if you get a piece of glass and look at the reflection of you're monitor, it only appears to be inches in front of you, not hundreds of feet. I can't find anything on the internet that explains how this works in a practical sense. I've read that the light needs to be "collimated" and I sort of understand what that means, but how do you do that? What kind of lenses do you need? Whats the math involved? The reason I'm asking is because I might be interesting in building one, just for fun.

You'd want to use a Fresnel lens for collimation. Most of the articles out there probably talk about using it for a projector, but the idea is similar. Your best bet would probably be to get one and play with it to find the right way to set things up, although they can get fairly expensive in large sizes.

 

[Urwumpe]

The trick is rather using a CRT and project the light of the CRT directly into the eye of the pilot. The collimation ensures that the HUD can be read and that the symbols are aligned with the line of sight of the pilot, eg, Horizon is where the pilot sees it

It is not magic...you can get kits in shops today.

 

[lockingtoggle]

Take a look at this http://www.mikesflightdeck.com/head_up_displays.htm

One thing to keep in mind if you build one is that you don't want it collimated, but focused at your projected scenery distance.