Question

what lens was used in the projecters

Answer 1

Concave lens.
Hope it helps!

Answer 2

The Distance from the center of the lens to the focal point is the focal length of the lens. The focal point is on the opposite side of the lens to that from which the light rays orginate. Convex are used in thinghs like telscones and binoculars to bring distance light rays to a focus in your eyes.

Answer Is:- Concav Lens.