Cheap camera lens for projector?

[Okta]

I have an idea to use a cheap wide angel camera lens like a 45mm .045x on my sharp 10x projector and maybe make a curved rear projection screen.

Does anyone have any experience with lenses and give me an idea of what i could achieve on the cheap? I can get a lens like that for around $40 off ebay but have no idea what it will do. I imagine it will make the projector short throw with a fish eye image? Would that be perfect for something like a J-dome?

Any insight appreciated.

[budda]

Hi,

I like your idea.

I don't have a definite answer for you, but I have looked into wide-angle optics for Wiimotes and webcams.

Some of the same principles apply, but in reverse for a projector.

Its important to match the focal length of the lens to the frame size of the image being projected. If the image at the focal plane is too wide for the lens to accomodate then much of the light won't make it out of the lens. Google "field of coverage" and "field of view" as this may help explain the situation.

Also "depth of field" is important. The further the screen is away from the projector and the shorter the focal length of the projector lens is, the less likely the projected image will be out of focus on a curved surface.

Also, remember there are lenses which are add-ons to cameras and these don't form images by themselves, whilst proper camera lenses can focus a real image onto the camera sensor. Projector lenses produce real images.

Also, look up "retro-focus lens" as these are the category of lens which apply here.

Optics is complicated, but no more than anything else.

Good luck.

[martinlandau]

Octa, halfway down this page, they say a spherical mirror is cheaper than a fisheye lens and better, what are your thoughts? It seems fisheye lenses are cheap.

http://www.icinema.unsw.edu.au/projects/infra_dome.html" onclick="window.open(this.href);return false;

Here is a guy who created "fisheye quake" which should mesh perfectly with all the quake engine games out there and a spherical or dome system.

http://strlen.com/gfxengine/fisheyequake/index.html" onclick="window.open(this.href);return false;