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I'm trying to do room-filling visuals with a standard projector. It's got a beam width of something around 25 or 30 degrees. Is it possible to (cheaply) widen that beam to near 180 and keep it in reasonable focus? I know that very expensive lens adapters exist, I'm wondering if anyone's done the math on this already and found the right combo of fresnel lenses and ellipses or some magic vodka bottle that bends light the right way.

The cheapest way would be to tie a rope to the projector and swing it around, kind of like an electron beam in a CRT.

Project onto a mirrored dome?

Buy some cheap lenses and try and see if you can approximate whatever you want. Close to 180 degrees might be hard though, what the heck are you doing with that?

The concept would be to take my Rock Demo style VJ performance and instead of just beaming it to a screen or a spot on a wall, to be able to spread the love around 2 or 3 sides of a room. My regular performance space is pretty small and dark, so the lumens budget covers it.

Here's an example effect

what about finding a second cheap projector?

and then the third to sixth cheap projectors \o/

how about http://www.amazon.com/Inch-Dome-Magnifier-Polishing-Pouch/dp/B000GAOCQ2/ref=pd_sim_ac_4?

or http://www.amazon.com/VISION-METALIZERS-DO8000-Mirror-Acrylic/dp/B007JCDJH8 (actual fulldome)

"Optical Grade Acrylic" -- oh come on :)

Optical grade acylic might be fundamentally wrong, but it's probably close enough for the resolution you're going to get from a beamer in this kind of use.

Also, since nobody's mentioned why we're talking about mirrored domes instead of lenses...

1. Mount projector vertically, facing down
2. Place mirrored dome under it to reflect the beam back
3. Realise your current tools don't support this weird new output mode, spend a week fixing them
4. Profit. Your beamer now covers 4 walls and the ceiling.

What about the shadow at the center?

...get an rgb laser that spins really really fast, code some hardware... done.

xtrim: yeah, you get a shadow directly overhead.

psonice: as xTr1m pointed out, you're better off keeping the ceiling out of the equation, got more to concentrate on the walls also keeps the output video slightly less complex. ;)

i remember once in my life i saw a lens, doing a trick like that. it was a overbent hemisphere lens. means a more cone then sphere. i guess a shader could correct the lens fail to project tho. anyway... iirc it was from a old light of a railway track.

This might provide some useful informations: http://paulbourke.net/miscellaneous/domemirror/

erm... http://paulbourke.net/miscellaneous/domemirror/