Interesting optics thread

[Enderman]

@LouieAtienza

Because the LCD screen will only allow light to pass through perpendicular to its plane the light has to be collimated to allow this. AFTER the light has left the LCD it is then focused on the projecting lens. You can argue about distortion all you want and are 100% right. But they’ve been making cheap projectors like this now for at least a decade. They’ve been using Fresnels in overhead projectors for decades.

As to Fresnel throwers… You can see in my pics I project an almost perfectly square die image - 200 yards into a brick wall. It’s rectangular now because I put a 2mm^2 in. I can’t capture it with my cell phone but at 40ft focused i could read the inscription on the MCPCB at 40ft. Possibly because the RLT moved on me and is illuminating the whole MCPCB.

So sure, I don’t expect a hi-def video projection. But you can search the thousands of YouTube videos of both DIY and cheap manufactued video projectors and see the image quality, while not great, is far better than you describe.

You weren’t talking about the LED when you said this, you were talking about a short throw projector:
“I think if you were building an ultra-short-throw video projector on the cheap, these could work great!”
A short throw projector needs to have an optical system that outputs light at a large exit angle, not collimate light from a light source with large incidence angles.

Also I see absolutely no retail digital projectors that use fresnel lenses on google, other than people that made a diy projector with an overhead projector and laptop screen.
And the only reason the image is even usable is because the light is going through a massive LCD that is 15” in size or something, not a regular projector LED which is usually less than one or two inches.