[DonRotolo]

Yes indeed, you need a lens in there somewhere to "project" the stencil image. Just LEDs and a stencil will give poor results.

Try it with a simple lens, like that in a magnifying glass. Cut a shape out of cardboard, and EXPERIMENT with a light source/lens/cutout combination. Often Light > Stencil > Lens works best. Different distances between those elements give different results.

Eventually you might try different lenses to see what works best.