Interference effects

Resolution is the ability to distinguish between two closely spaced objects. For example, when the headlights of a car are sufficiently far away and all you see is a single point of light, you have failed to resolve the headlights. Another example: the naked eye cannot resolve the three stars that appear as one in the Big Dipper—a telescope of greater resolution is required.

The resolution of an optical device such as a camera, microscope, or telescope can be limited by imperfections in the lens itself. However, there is a fundamental limit on any optical imaging system due to the diffraction of light waves. The smaller the opening of a camera’s aperture or an eye’s pupil, the more the light will diffract and interfere with itself, reducing resolution. If the opening remains constant, this will still happen if there is more magnification (as optical power increases).

Another interference effect is polarization, discovered by Edwin Land in the early 1920s. It works by blocking certain orientations of transverse waves using a series of long, parallel crystals:

Polarized sunglasses use vertical filters to block part of the incoming light. They are vertical because glare is usually parallel to the surface of reflection, which is horizontal for the ground. This is useful when the snow is painfully bright on a sunny day, or when you are out on the water.