Eyepiece, what is the objective lens?

Eyepieces and objective lenses are both convex lenses.

Introduction to convex lens:

A convex lens is a common lens with a thick middle and thin edges. At least one surface is made into a spherical surface, and both sides can be made into spherical surfaces. Play the role of amplification. Multiples vary.

Principle

Convex lenses have a magnifying effect. Convex lenses are divided into large and small at twice the focal length, and are divided into real, virtual, upright and inverted at one focal length.

Inject parallel light rays (such as sunlight) parallel to the main optical axis (the line connecting the centers of the two spherical surfaces of the convex lens is called the main optical axis of the lens). The light passes through both sides of the lens. After secondary refraction, it is concentrated on a point on the axis. This point is called the focus of the convex lens (marked as F, English: focal point). The convex lens has a real focus on both sides of the mirror. For example, when it is a thin lens, these two focuses are The distances between the lens centers are approximately equal. The focal length of a convex lens refers to the distance from the focus to the center of the lens, usually expressed as f. The smaller the spherical radius of the convex lens, the shorter the focal length (symbol: f, English: focal length).

Convex lenses can be used in magnifying glasses, glasses worn by people with presbyopia and farsightedness, cameras, movie projectors, slide projectors, microscopes, telescope lenses, etc. Main axis of convex lens: The straight line passing through the two spherical centers C1 and C2 of the convex lens is called the main optical axis of the convex lens. Optical center: The center point O of the convex lens is the optical center of the lens. Focus: The light rays parallel to the main axis converge at a point F on the main optical axis after passing through the convex lens. This point is the focus of the convex lens. Focal length: The distance from the focal point F to the optical center O of the convex lens is called the focal length, represented by f. Object distance: The distance from the object to the optical center of the convex lens is called the object distance, represented by u. Image distance: The distance from the image formed by an object through a convex lens to the optical center of the convex lens is called the image distance, represented by v.