Achromatic lens, also known as doublet lenses, are made of two concave and convex lenses with different refractive indices and dispersion rates, which can minimize or eliminate chromatic aberration. Achromatic doublet lenses are widely used in the aerospace field, such as in the manufacture of aircraft cabin windows, space telescopes, satellites, etc.; medical equipment, such as microscopes, endoscopes, surgical instruments, etc.

In order to obtain better performance, the side with a larger radius of curvature (flat surface) should usually be away from the collimated beam. Chromatic aberration originates from the difference in dispersion and refractive index of light of different wavelengths in the transmission material, which makes light of different wavelengths converge at different focal points. Double-cemented achromatic lenses use the bonding design of lenses of different materials to make the dispersion of the two materials compensate for each other, thereby reducing the comprehensive chromatic aberration. 

The achromatic design also helps to improve the aberration of imaging of light sources (composite light sources) with a wide wavelength range, improve spherical aberration at a suitable radius of curvature, and improve coma at the same time when any material is selected. Compared with an optical system using a single lens, an achromatic lens has a sharper image and can form a smaller light spot, further improving the optical performance of the lens. Achromatic lenses are suitable for various applications such as fluorescence microscopy, telescopes, image relay, detection, or spectroscopy.