May.26, 2022

**Double Concave Lenses** are also called negative spherical lenses or bi-concave lenses, of which the middle is thin and the edge is thick and concave. Concave lenses have a diverging effect on light. Double concave Lenses are used in beam expansion, image reduction, or light projection applications. These lenses are also ideal for expanding the focal length of an optical system.

**Concave lenses** are divided into double concave/ biconcave, plano-concave, and convex-concave (note: convex-concave lenses are more concave than **convex**, concave-convex lenses are more convex than concave!), etc. Today we would like to explain the double concave lens uses specifically.

After the deflection of the parallel light through the **concave spherical lens**, the light diverges and becomes a diverging light, which cannot form a real focal point. Along the reverse extension of the diverging light, which intersects the same side of the projected light at point F, an imaginary focal point is formed.

Three special lights of a concave lens

(A concave lens has two imaginary focal points)

The geometrical drawing of a concave lens is based on the same principle as that of a convex lens. From the top of the object, there are also two straight lines: one parallel to the main optical axis, which is deflected into a diverging ray after passing through the concave lens, and this refracted ray is returned to the main focus in the opposite direction; the other passes through **the ****optical center of the lens**, and these two lines intersect at a point, which is the image of the object.

The object and the image are on the same side of the lens. 1/u (object distance) + 1/v (image distance) = 1/f (focal length of the lens) lens imaging formula

(On the sign of the positive and negative: object distance u to take positive values, ν and f to take negative values.)

When an object is a physical object, into a positive, reduced virtual image, image, and object on the same side of the lens; when the object is virtual, the distance from the concave lens to the virtual object is double the focal length (refers to the absolute value of u < f) or less, into a positive, magnified real image, image and object on the same side of the lens; when the object is virtual, the distance from the concave lens to the virtual object is double the focal length (refers to the absolute value of u = f), imaging at infinity; when the object is virtual, the distance from the concave lens to the virtual object is double the focal length (refers to the absolute value of u = f) When the object is imaginary, the distance from the concave lens to the imaginary object is twice the focal length outside the double focal length (both refer to the absolute value of f < u < 2f), into an inverted, magnified.

When the object is imaginary, the distance from the concave lens to the imaginary object is twice the focal length (refers to the absolute value of u=2f), the imaginary image is of the same size as the object, the image and the object on the opposite side of the lens; When the object is imaginary, **the distance from the concave lens to the imaginary object** is twice the focal length (refers to the absolute value of u>2f), the imaginary image of the inverted, reduced, the image and the object on the opposite side of the lens.

The case of a thick curved moon shape will be more complicated. It is equivalent to a Galilean telescope when the thickness is large enough, and to a positive lens when the thickness is greater.

Concave Lens Astigmatism

There are three types of lenses: **biconcave**, plano-concave, and convex-concave. The line connecting the centers of curvature on both sides is called the principal axis, and the central point O is called the optical center. The light passing through the optical center is not refracted no matter where it comes from. The light beam of the parallel main axis, shining on the concave lens refracted to the four directions of dispersion, the extension of the direction of dispersion will be on the same side of the light source at point F, the refraction of the light as from the F point, this point is called the virtual focus. There is one on each side of the lens. A concave lens is also called a diverging lens. The focal length of a concave lens is the distance from the focal point to the center of the lens. The larger the radius of the lens, the longer its focal length, such as a thin lens, the focal length of both sides of the lens is equal.

Both sides are spherical or one side is spherical and the other side is a flat transparent body, the middle part is thinner, called the concave lens. When used in light sparse medium, can play a diverging role on the incident light beam, so also known as diverging lens. And because its focal length is negative, also known as a negative lens. For a thin concave lens, the imaging formula, the transverse magnification formula, and the sign rule are the same as for a convex lens.

The image formed by **a concave lens** is always smaller than the object, upright virtual image, concave lenses are mainly used to correct myopia. Myopia is mainly due to the deformation of the lens, which causes light to collect prematurely in front of the retina. The concave lens plays a role in dispersing the light, and the concave lens becomes an orthogonal, reduced virtual image, making the image distance longer and falling exactly on the retina.

**RZ Optics Co., Ltd.** manufactures a wide range of large optical lenses, such as plano-convex lenses, Plano concave lenses. We can also perform custom optical coatings for large lenses, including anti-reflection, and V-coating. **View our product catalog**

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