Ok, a lens is held upright with a piece of clay. In front of it is a bulb, and behind it is a screen at the location of the image of the bulb. Now, what would happen to the image if the top half of the lens were covered by a mask? And what if the mask had a small hole in the center and were placed in front of the lens? This is an extra credit lab, and I have been trying to figure it all out on my own, but this question I really have no idea.