Optical Lens Types

Optical lenses have been used for centuries. Telescopes, binoculars, glasses and microscopes have all helped us to see better than we can with the naked eye. Lenses focus the beams of the lasers we rely on to play our CDs and DVDs. Lenses gather light of the subjects we photograph. Lenses correct our sight. It is safe to say that if we did not have lenses, we would not be as advanced as we are right now.

Achromatic Lenses

• Achromats are made of two or more lenses that are affixed in relation to each other by mounting or cement. Achromats are a common type of viewing lens. The lenses comprising an achromat are corrected for chromatic aberration in two wavelengths. These are commonly referred to as achromatic lenses. Achromats are specifically designed to work within the ultra-violet, visible and infrared spectrums. Achromats are not symmetric, in that have to be set in the correct order, front to back. If not installed properly, the image will be distorted badly.

Cylindrical Lenses

• Cylindrical lenses, as the name implies, have at least one or more surfaces that are cylindrical in shape. Cylindrical lenses are used to correct astigmatisms, or in the case of rangefinders, to create an astigmatism to stretch a point of light into a line. Cylindrical lenses may have an anti-reflective coating to increase transmission of light.

  Cylindrical lenses can be in plano-convex or plano-concave types. Plano-convex lenses are of a positive focal length making them collect and focus light, while plano-concave lenses are of a negative focal length and spread and reduce light.

Fresnel Lenses

• A Fresnel lens is a plano-concave or plano-convex lens that is flat on one side and has concentric rings cut into it. A common use for Fresnel lenses is spotlights. Like cylindrical lenses, Fresnels can be positive or negative in focal length. Fresnels designed for use in infrared applications are designed for use in the 750nm (nanometer) to 2500nm wavelength. Fresnels intended for visible light uses are designed for use in the 380nm to 750nm wavelength, and Fresnels intended for use in ultraviolet applications are designed for use in the 4nm to 380nm wavelengths.