###### ♤Products > Lenses

# Spheric & Aspheric Lenses

Lenses are used for imaging, focusing or dispersing a light beam. UV fused
silica lens is used in UV and high power laser. N-BK7, Crown and Flint glass are
used for visible and NIR imaging. Gemanium, Silicon and ZnSe are used for IR systems.

### Simple lenses

Lenses are classified by the curvature of the two optical surfaces:
Plano-convex, plano-concave, Double-convex, Double-concave, Meniscus.

The focal length of a lens in air can be calculated from the lensmaker's equation:

###### 1/f = (n-1)[ 1/R1 - 1/R2 + (n-1)d/nR1R2 ]

where

f is the focal length of the lens,

n is the refractive index of the lens material,

R1 is the radius of curvature (with sign, see below) of the lens surface closer to the light source,

R2 is the radius of curvature of the lens surface farther from the light source, and

d is the thickness of the lens.

The focal length f is positive for converging lenses, and negative for diverging lenses.

The signs of the lens' radii:
positive R indicates a surface's center of curvature in the right side,
negative R indicates surface's center in the left.

Thin lens formula:

###### 1/S1 +1/S2 = 1/f

### Achromatic Doublet

Chromatic aberration: caused by the dispersion of the lens material

Low dispersion material such as CaF2 crystal, or
achromatic doublet in which two materials with differing dispersion
are bonded together, are used to reduce chromatic aberration.

### Aspherical best form lens

Spherical aberration: spherical aberration occurs because spherical surfaces are not the ideal shape for a lens.

Coma: Coma occurs when rays pass through the lens at an angle to the axis θ.

Aspherical best form lenses are designed to correct Spherical aberration,
Coma and Chromatic aberration.

### Lenses Order Information

Optocity offer advanced aspheric glass lenses for security surveillance,
driving recorder etc. Singlet, doublet, cylinder, ball lens, Grin lens and other type of lenses
are also available from Optocity. Please send us an e-mail to request for quote.

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