# Do You Know Double-Concave Lenses?

Feb. 24, 2020

Double concave lens supplier share with you:

1. A biconcave lens is similar to a plano-concave lens, with a negative focal length, but the rays of light incident in parallel diverge outward. The two sides of the biconcave lens have the same radius of curvature, and are generally used for beam expansion and projection.

Focal length of 2 biconcave lenses

As shown in the figure, the spherical radius corresponding to the front concave surface of the biconcave lens is r1, and the spherical radius corresponding to the back concave surface of the biconcave lens is r2.

Biconcave lens

As the auxiliary line is shown by the dotted line, the biconcave lens can be regarded as a combination of two plano-concave lenses.

3 Principles

The geometric mapping of double concave lens imaging is the same as the principle of convex lens. From the top of the object, it also acts as two straight lines: one parallel to the main optical axis and deflected into divergent light after passing through the biconcave lens, returning this refracted light to the main focus in the opposite direction; Lines intersect at a point, this is the image of the object.

4Differences between biconcave lenses and plano-concave lenses

Convex and concave lenses are used for myopia; convex and concave lenses are used for reading glasses; plano-convex lenses are used for instruments or magnification; plano-concave lenses are used for instruments.

Plano-concave lenses are lenses that are concave on one side and flat on the other, while bi-concave lenses are lenses that are concave on both sides.

5 uses:

The line connecting the centers of curvature on both sides is called the principal axis, and the point O at the center is called the light center. Light that passes through the center of light is not refracted no matter where it comes from. The light beam parallel to the main axis diverges in four directions after being refracted on the concave lens, and the extension lines opposite to the direction of divergence will be at a point F on the same side as the light source. . There is one on each side of the lens. A biconcave lens is also called a divergent lens. The focal length of a concave lens refers to the distance from the focal point to the center of the lens. The larger the lens radius, the longer the focal length. If it is a thin lens, the focal lengths on both sides are equal.

When used in optically sparse media, it can diverge the incident beam, so it is also called a divergent lens. Because its focal length is negative, it is also called a negative lens. For thin concave lenses, the imaging formula, lateral magnification formula, and sign rule are the same as for convex lenses.

The image formed by a biconcave lens is always smaller than an object, an upright virtual image. The biconcave lens is mainly used to correct myopia. Myopia is mainly caused by the deformation of the lens, causing the light to collect prematurely in front of the retina. The biconcave lens plays the role of diverging light. The biconcave lens forms an upright, reduced virtual image, which makes the image distance longer and falls on the retina. Double Concave Lens 