How does a microscope work?

A microscope works by producing an enlarged image of a small object.

Because the eye can only focus to about 10 in (25 cm), this limits its ability to see fine detail by simply moving in closer. A magnifier has a much shorter focal length and produces a beam of parallel rays that the eye treats as coming from infinity. The eye has no problem focusing these rays, so it can now comfortably see a blown-up image as if it were at the position of the magnifying glass. In essence, the magnifier lets the eye work at a much closer distance where it can see a larger image.

A microscope works the same way as a simple one-element magnifier, using a series of lenses to provide a very short effective focal length and correspondingly high magnifications.

Updated 12/18/13