How does the projector work?

Hint 1 of 8:

Have you examined it?

Hint 2 of 8:

What are the items that can be controlled on the projector?

Hint 3 of 8:

You can turn it on/off.

Hint 4 of 8:

You can turn the dial.

Hint 5 of 8:

The dial only has two settings. In/out of focus.