The Zeiss Tessar
1902
Paul Rudolph’s four-element lens for Zeiss: sharp, compact and simple to make. Sold as the eagle eye of the camera, it was copied by almost every maker.
How it began
Paul Rudolph, a mathematician turned designer at Zeiss, had already made the Protar and the Unar. In 1902 he combined ideas from both into a four-element lens and named it Tessar, from the Greek for four.
How it works
Like the cooke triplet it has two convex lenses around a concave one, but the rear convex lens is a cemented pair of different glasses. That extra freedom corrects colour and edge sharpness better, without adding air spaces that would scatter light.
Why it mattered
The Tessar gave high sharpness at moderate cost and size, and Zeiss licensed it widely. It became the standard lens on good folding cameras, twin-lens reflexes and early 35mm cameras, and was imitated under dozens of names once the patent ran out.
Limits and what replaced it
Its aperture stayed modest, around f/2.8 at best. Faster lenses, such as Double Gauss designs like the Planar, took over for low light, and computer-designed lenses for wide angles and zooms.
Today
Tessar-type lenses still appear in fixed-lens cameras and enlargers, and Zeiss uses the name on phone lenses.