Schematic diagram of the imaging principle of convex lens

The principle of convex lens imaging is as follows:

Convex lens imaging is a phenomenon of refraction of light. The principle is that convex lenses have a converging effect on light. When a convex lens forms a real image, after the light emitted from a certain point on the object is refracted by the convex lens, the refracted light rays intersect at a point, which is the image point of that point on the object. In the same way, the light emitted by other points on the object is refracted by the convex lens and then refracted by the convex lens. Corresponding image points are formed, and these image points together form a complete image of the object. The image can be displayed on the light screen and is a real image.

When a convex lens forms a virtual image, after the light emitted from a certain point on the object is refracted by the convex lens, the refracted rays cannot intersect, but the reverse extension lines of the refracted rays (the dotted line in the figure below) can intersect, and the intersection point is For the virtual image point of that point on the object, in the same way, the light emitted by other points on the object becomes a corresponding virtual image point after being refracted by the convex lens. These image points together constitute a complete virtual image of the object. The virtual image cannot be presented on the light screen. Can be observed directly with eyes.

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. If it is a thin lens, these two focuses reach the lens. The centers are roughly the same distance apart.

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: focallength). 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 optical axis: 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.

In fact, neither convex lenses nor concave lenses have a certain focus. Only light rays parallel to the main optical axis 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 light rays passing through a convex lens that are parallel to the main optical axis but unequal distance from the main optical axis have a "focus" is because the curvature radius of the convex lens mirror is large and the light rays are deflected. The difference in degree is not obvious. For ease of use, we take the intersection point of two rays at an equal distance from the main optical axis and the top of the convex lens as the focus of the convex lens.