Explain why the back side of an aquarium can appear to be silvery and reflective from some directions, even though you can see through it from other directions. Discuss the proper position of a slide relative to the lens in a slide projector. What type of lens must the slide projector have? A pair of red lights that are mounted 1 meter apart are far enough away so that they are barely resolvable as two sources. A similar pair of blue lights (also 1 meter apart) is also mounted far enough away as to be barely resolvable. Which pair of sources is farthest from the observer?