✔ 最佳答案
If I understand your problem, the issue is with the definition of the bat shape.
This may be caused by how the beam leaves the lamp. If you look at different types of floodlights and spotlights (look here:
http://www.theatrecrafts.com/lx_lanterns.html ) then you may better understand what I mean.
Your best bet is to find a way to focus the beam by using some sort of lens. How to do this cheaply is a bit of a challenge, but if you go through a scrapyard you may find old mirrors or pieces of glass that may work... a lot of trial an error, I am afraid. If you find an old projector that somebody has discarded, you will be in luck!
You can also try to add distance between the beam source and the cardboard cut-out, however I think this may produce only a minor improvement.
The project sounds cool, good luck!