History of photographic lens design is) also popular as a telephoto lens design – the Sonnar is always at least slightly telephoto because of its powerful front positive elements. The Zeiss Olympia Sonnar 180mm f/2.8 for the Contax II (both 1936, Germany) is a classic, if not mythic, example. In 1817 Carl Friedrich Gauss improved the Fraunhofer telescope objective by adding a meniscus lens to its single convex and concave lens design. Alvan Clark further refined the design in 1888 by taking two of these lenses and placing them back to back. The lens was named in honour of Gauss. The current design can be
Lens (optics) real object at the location of that virtual image. Likewise, it appears to a subsequent lens as if it were an object at that location, so that second lens could again focus that light into a real image, "S" then being measured from the virtual image location behind the first lens to the second lens. This is exactly what the eye does when looking through a magnifying glass. The magnifying glass creates a (magnified) virtual image behind the magnifying glass, but those rays are then re-imaged by the lens of the eye to create a "real image" on the retina.