Can I place a lens in front of a projector?

I'm trying to figure out if it's possible to just place a lens a few inches in front of a commercial projector to magnify the image. I just drilled a pair of 3" holes on my wall (one needs to be up'd to 4") so that I can have my projector in one room projecting into the other.

It works great, except I'd like to make the image a bit larger.

I'm looking for 2x (I think... 100"-->200". is that 4x?) magnification at 10'. Any suggestions how to go about this?

I know little about optics, but I think I'd still be able to use the focus controls on the projector, correct? Or would i need a new way to focus?

Thanks!


I'm hoping I can do something simple like just adding a 100mm (diameter) double-concave lens in the hole in my wall.
 
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