Resolution - the fundamental characteristic of optical instruments

All optical devices, regardless of their specificity and purpose, necessarily have one common physical characteristic, called "resolution". This physical property is the determining one for all optical and optical-measuring devices, without exception . For example, for a microscope, the most important parameter is not only the magnifying power of its lenses, but also the resolution, on which the quality of the image of the object under investigation directly depends. If the design of this device is not capable of providing a separate perception of the smallest details, the resulting image will be of poor quality even with a significant increase.

The resolving power of optical instruments is a quantity that characterizes their ability to distinguish the smallest individual parts of observable or measurable objects. Limit resolution is the minimum distance between adjacent details (points) of the object, in which their images are no longer perceived as separate elements of the object, merging into one. The smaller this distance, the higher the resolving power of the device, respectively.

The inverse resolution limit is a quantitative measure of the resolving power. This most important parameter determines the quality of the device and, accordingly, its price. Due to the diffraction property of light waves, all images of small elements of the object have the form of light spots surrounded by a system of concentric interference circles. This phenomenon serves as a limitation of the resolving power of any optical devices.

According to the theory of the English physicist Rayleigh of the 19th century, the image of two nearby small elements of the object can still be discerned when their diffraction maximum coincides. But even this resolution has its limit. It is determined by the distance between these minute details of objects. The resolving power of an objective is usually determined by the maximum number of separately perceived lines per one millimeter of the image. This fact was established experimentally.

The resolving power of the instruments is reduced in the presence of aberrations (deviations of the light beam from a given direction) and various errors in the fabrication of optical systems, which increases the dimensions of the diffraction spots. Thus, the smaller the magnitude of the diffraction spots, the higher the resolving power of any optics. This is an important indicator.

The resolving power of any optical device is evaluated by its hardware functions, reflecting all the factors that affect the quality of the image provided by this device. To such influencing factors, of course, first of all, aberration and diffraction should be attributed - the enveloping of obstacles by light waves and, as a consequence, their deviation from the rectilinear direction. To determine the resolution of various optical instruments, special test transparent or opaque plates with a standard pattern, called worlds, are used.