scott <sco### [at] scottcom> wrote:
> > If a parabola reflects parallel lines into its focus,

What if your parabola began to focus those parallel rays, and then intersected a
divergent lens - then you might get back parallel rays, only in the opposite
direction.

Maybe take a look at the construction of a Dobsonian telescope or "light
bucket".
http://en.wikipedia.org/wiki/Dobsonian_telescope

Also, if you simply had flat mirrors mounted to the side of the cylinder, you
could then reflect light straight back onto the grass after it completed its
U-turn.

Allow me to construct athroroughly abyssmal ASCII diagram:

/--\ /--\
^  | |  ^
|   O   |
    ^   light
    |
    cylinder

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