Calcium Fluoride (CaF₂)
Plano-Convex Lenses

Plano-convex (PCX) lenses are positive lenses which are thicker in the middle than at the edge, when collimated rays go through them, light converges to a physical focal point. Plano-convex lenses have one flat side and one curved side with a positive radius of curvature. Plano-Convex lenses have a positive focal length and approach best form for infinite and finite conjugate applications. These lenses focus a collimated beam to the back focus and collimate light from a point source. They are designed with minimal spherical aberration and have a focal length given by:
f= R/(n-1),
where R is the radius of curvature of the convex portion of the lens and n is the index of refraction.

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Plano-convex lenses deliver less spherical distortion when focusing at infinity (when the imaged object is far away and the conjugate ratio is high). Therefore they are the go-to lens in cameras and telescopes. Maximum efficiency is achieved when the plano surface faces the desired focal plane, in other words, the curved surface faces the collimated incident beam. Plano convex lenses are a good choice for light collimation or for focusing applications utilizing monochromatic illumination, in industries such as industrial, pharmaceutical, robotics, or defense. They are an economical choice for demanding applications because they are easy to fabricate. As a rule of thumb, plano-convex lenses perform well when the object and image are at absolute conjugate ratios > 5:1 or < 1:5, so spherical aberration, coma and distortion are reduced. When the desired absolute magnification is between these two values, Bi-convex lenses are usually more suitable.

Due to its high transmission from 0.18 µm to 8.0 μm, CaF₂ exhibits a low refractive index varying from 1.35 to 1.51 and is commonly used for applications requiring high transmission in the infrared and ultraviolet spectral ranges. Calcium fluoride is also fairly chemically inert and offers superior hardness compared to its barium fluoride, and magnesium fluoride cousins. Paralight Optics offers Calcium Fluoride (CaF₂) plano-convex lenses with antireflection coatings for either the 1.65 µm to 3.0 µm or 2 µm to 5 µm wavelength range. This coating greatly reduces the average reflectance of the substrate less than 1.25%, yielding a high average transmission greater than 95% across the entire AR coating range. Check the following Graphs for your references.