How to distinguish an objective lens from an eyepiece?

The way to distinguish the objective lens from the eyepiece is that the eyepiece is installed at the upper end of the lens barrel, which is a lens close to the human eye. The objective lens is installed on the converter at the lower end of the lens barrel, close to the lens for observing the object. The eyepiece is usually inserted directly into the lens barrel, and the objective lens is mostly screwed on.

The structure of eyepiece is much simpler than that of objective lens. The eyepiece consists of two parts, and the lens at the upper end is called the eye lens, which plays a magnifying role. The following lens is called a converging lens or a field lens, which makes the image brightness uniform. There is a diaphragm in the middle of the upper and lower lenses or at the lower end of the lower lens, and accessories such as micrometer, cross glass and pointer are installed on the diaphragm.

The objective lens is complex in structure and precise in manufacture, and usually consists of lens groups, and the lenses are separated by a certain distance to reduce the phase difference. Each lens group consists of one or several lenses with different materials and parameters, and the objective lens has many specific requirements, such as focusing and focusing. The working beam of the eyepiece is narrow, but the inclination angle is large. When calculating the objective lens and eyepiece, there is a great difference in eliminating aberration. The objective lens is the most complicated and important part of the microscope. It works with a wide beam with a small inclination to the optical axis.

Eyepiece type

1, Fogan eyepiece: The main focus of the positive eyepiece is outside the objective lens. Although it is composed of two or more lenses, the whole optical system can be regarded as a single convex lens, so it can be used as a magnifying glass alone under appropriate circumstances.

2. Reston eyepiece: It consists of two plano-convex lenses, and its main focus is outside the lower lens (field lens), so it is called a positive lens. Reston eyepiece has a good correction for image field bending and distortion, and the spherical aberration is also small, but the magnification chromatic aberration is worse than Fogan eyepiece. It can be used not only for observation and photography, but also for magnification.

3. Compensating eyepiece: Flat-field achromatic objective lens and flat-field semi-achromatic objective lens with vertical chromatic aberration of 1.5%-2% are all objective lenses with insufficient vertical chromatic aberration correction. These objective lenses need to be used in conjunction with the eyepiece with excessive vertical chromatic aberration correction, so this eyepiece is called compensation eyepiece.

Reference to the above content: Baidu Encyclopedia-Eyepiece