The Cooke triplet is a photographic lens design designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by Cooke of York. It was the first lens system that allows elimination of most of the optical distortion or aberration at the outer edge of lenses.
A Cooke triplet comprises a negative flint glass element in the centre with a crown glass element on each side.
It was at that time a major advancement in lens design. The triplet design was made obsolete by later designs on high end cameras, but remained widely used up to this day on cheap cameras.
Despite the fact that the Cooke design was patented in 1893 it seems that the use of achromatic triplet designs in astronomy appeared as early as 1765. The 1911 encyclopedia Britanica wrote:
- "The triple object-glass, consisting of a combination of two convex lenses of crown glass with a concave flint lens between them, was introduced in 1765 by Peter, son of, John Dollond, and many excellent telescopes of this kind were made by him."
