Resolving Power of Optical Instruments

Resolving power of an optical instrument the is its ability to show to close lying objects as the separate entities in its image. This is different from magnifying power. It is not about increasing the size of the image. But it is about identifying the image of different bodies separately.

Consider a parallel beam of light falling on a convex lens. All the beam of the light rays are supposed to focus at a particular point. However due to the diffraction, instead of the beam pointing out at a particular point it is focused at a finite area. The image pattern consists of central bright region surrounded by concentric dark and bright regions as shown below.

Resolving power of a microscope

A microscope resolves the linear distance between two close objects. In the diagram shown the convex lens is having an aperture. Two different possible light rays at the two extremely ends forms two different images and identifying them separately is called resolving power. Resolving limit is the reciprocal of resolving power.

Resolving power of a telescope

A telescope gives resolution between two for away objects. We can explain that the resolving power of a telescope is directly proportional to aperture of the lens and inversely proportional to wavelength of the light used.