Achromatic lens

Invented by : Johan Dollond

Invented in year : 1758

An Achromatic Lens is those Lens which are designed to limit the effects of chromatic and spherical aberration. Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus in the same plane. It is also known as Achromat. The most common type of Achromat is the Achromatic Doublet, which is composed of two individual lenses made from glasses with different amounts of dispersion. Usually, one element is a concave lens made out of flint glass, which has relatively high dispersion, while the other, convex, element is made of crown glass, which has lower dispersion. The lens elements are mounted next to each other, typically cemented together, and shaped so that the chromatic aberration of one is counterbalanced by that of the other.

The origin of Achromatic Lens can be traced back to 1733. During this time Optician George Bass, following the instructions of Chester Moore Hall, made and sold such lenses. However, John Dollond, an English Optician, was the first person to patent the Achromatic Lens in 1758. His competitors, including Bass, Benjamin Martin, Robert Rew and Jesse Ramsden, took action against the patent which was upheld. The court found that the patent was valid due to Dollond's exploitation of the invention while prior inventors did not. Therefore he is considered as the Inventor of the lenses. in 1757 he succeeded in producing refraction without colour by the aid of glass and water lenses, and a few months later he made a successful attempt to get the same result by a combination of glasses of different qualities. In 1758, he published an "Account of some experiments concerning the different refrangibility of light", describing the experiments which led to the discovery of a means of constructing achromatic lenses by the combination of crown and flint glasses.

Role of Achromatic Lens in the Improvement Of Human Life

The early lenses tended to break up white light into its constituent parts. This technical problem was solved with the invention of achromatic lenses

An unforeseen benefit of the achromatic lens was their larger diameter, which created greater magnification. Because on-axis achromat performance will not deteriorate with larger clear apertures, "closing down" the optical system becomes unnecessary. With the entire clear aperture utilized, achromats and achromatic systems are faster, more efficient, and more powerful resulting in brighter images and better energy throughput

It found its usage in the Achromatic Telescope which is a refracting telescope that uses an achromatic lens to correct for chromatic aberration.

Achromatic Lenses have benefited both still and motion-picture photography. A major objective that has been achieved was the ability to properly focus all the colours of the image at the film plane.

Better lenses and camera designs were improved and reinvented as a result of Achromatic Lenses. An achromatic portrait lens was about 20 times faster than the simple meniscus lens

Having eliminated the problematic chromatic aberrations, achromatic lenses became the most cost-efficient means for good polychromatic illumination and imaging.