It's a known fact that when you partially cover a lens (with fabric or something), the image on the other side would look less illuminated, since less light rays go through the lens. However, what happens when you partially cover a concave/convex mirror? Our teacher thinks the same thing happens, the image looks less illuminated. I, and some other pupils, think that by covering the mirror you reduce the "field of eyesight", i.e the number of places from which you can fully see the object in the mirror. Can anyone confirm either claims, and explain why?