Convex lens principle

The convex lens has a magnifying effect. The secondary focal length of convex lens is divided into two parts, and the primary focal length is divided into real, imaginary and inverse.

Parallel light (such as sunlight) is parallel to the main optical axis (the line connecting the spherical centers of the convex lens is called the main optical axis of the lens). After the light is refracted twice on both sides of the lens, it is concentrated at a point on the axis, which is called the focus of the convex lens. A convex lens has a real focus on both sides of the mirror. If it is a thin lens, the distance between the two focal points and the center of the lens is approximately equal. The focal length of the convex lens refers to the distance from the focal point to the center of the lens, which is usually expressed by F. The smaller the spherical radius of the convex lens, the shorter the focal length (marked as F, English: focal length). The convex lens can be used for magnifying glasses, glasses worn by presbyopia and hyperopia, cameras, film projectors, slide projectors, microscopes, telescopes, etc. Principal axis: a straight line passing through the two spherical centers of convex lens C 1 C2 is called the main optical axis of the convex lens. Optical center: the central O point of the convex lens is the optical center of the lens. Focus: the light parallel to the main axis passes through the convex lens and converges at a point f on the main optical axis, which 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 focal length, which is denoted by f. Object distance: the distance from the object to the optical center of the convex lens is called object distance, which is denoted by u. Image distance: the distance from the image formed by the object through the convex lens to the optical center of the convex lens is called image distance, which is denoted by v..

In fact, neither convex lens nor concave lens has a certain focal length, and only light rays parallel to and at the same distance from the main optical axis will completely intersect on the main optical axis. The reason why we see that many rays parallel to the main optical axis but not at the same distance from the main optical axis all have "focus" through the convex lens is because the curvature radius of the convex lens mirror is large, and the difference of light degree deflection is not obvious. For the convenience of use, we take the intersection of two rays with the same distance between the main optical axis and the top of the convex lens as the focus of the convex lens.