@seetheleaves: Glad to have helped.
@David: Thanks for pointing that out. I did not consider the intensity of light in my explanation. Mirrors that are "perfectly" flat, and therefore perfectly reflective are very, very rare, and so most mirrors (and lenses too) will "lose" some of the light (in the case of mirrors, some light is transmitted into them; in the case of lenses, some light is reflected and never reaches the eye) and the resulting image is not as intense (or as "sharp") as the actual object. But if I'm not mistaken, the difference is greater in lenses (like glasses) than in the average mirror, which tends to reflect light pretty well.