8C20.40 and 8C20.45 Gravitational Lensing
A bright light can be shined through two machined plexiglass lenses and onto a screen. Or, objects on a desk can be viewed through the lenses and projected overhead. The lenses bend the light like a black hole and a diffuse cluster, respectively. Einstein rings and multiple images can be produced.
[Set-up time: please give advanced notice]