Optical lens for diving mask

Double concave lens is similar to flat concave lens. The focal length is negative, but the light incident in parallel diverges outward. The curvature radii of the two sides of double concave lens are equal. It is generally used for beam expansion and projection.

The principle of geometric drawing of biconcave lens imaging is the same as that of convex lens. The top of the object is also regarded as two straight lines: one is parallel to the main optical axis, deflects into divergent light after passing through the biconcave lens, and returns the refracted light to the main focus in the opposite direction; The other passes through the optical center point of the lens. The two straight lines intersect at one point, which is the image of the object.

When used in light sparse medium, it can diverge the incident beam, so it is also called divergent lens. It is also called negative lens because its focal length is negative. For thin concave lens, the imaging formula, transverse magnification formula and sign rule are the same as those for convex lens.

The image formed by biconcave lens is always smaller than the vertical virtual image of the object. Biconcave lens is mainly used to correct myopia. Myopia is mainly due to the deformation of the lens, resulting in the premature collection of light in front of the retina. The biconcave lens plays the role of divergent light. The biconcave lens becomes an upright and reduced virtual image, which lengthens the image distance and just falls on the retina.