Is their friendship worth more than the camera?
My father had a policy of never lending someone something. Either give it to them, which if they felt inclined they could give it back, or don't lend at all. This went for money as well as objects. He felt the friendship or family connection was far more important than some things, other things he just didn't lend out.
I wouldn't push the issue too much, there's not much that can be done if they don't feel remorse for what happened.