The eyepiece is used to observe the image of the front optical system into the visual optical device, is a telescope, microscope and other visual components of optical instruments, the main role is to magnify the real image obtained by the objective lens magnification again. In order to eliminate aberration, the eyepiece is usually made up of a number of lenses, with a large field of view and angle of view magnification.
The eyepiece is also the main component of the microscope, its main role is to magnify the real image obtained by the objective lens magnification again, so as to form a clear virtual image at the distance of the bright vision; therefore, its quality will finally affect the quality of the object image. In micrographs, a solid image is formed at the hair glass. Some eyepieces (e.g., compensating eyepieces), in addition to magnification, can be corrected for residual aberrations produced during the imaging process of the objective lens.
Eyepieces are much simpler to construct than objective lenses. Because the beam through the eyepiece is close to parallel state, so the spherical aberration and longitudinal (axial) chromatic aberration is not serious. Eyepieces designed to consider only the transverse chromatic aberration (magnification chromatic aberration), composed of two parts, located in the upper end of the lens is called the eye lens, plays a role in magnification; the lower end of the lens is called the convergence lens or field lens, so that the brightness of the image is uniform. In the middle of the upper and lower lenses or the lower end of the lower lens, there is a light bar, micrometer, cross glass, pointer and other accessories are installed here. Eyepiece aperture angle is very narrow, its own resolution is very poor, but the preliminary image of the objective lens has been sufficient to magnify.
