The Biogon 21mm f/4.5 is an ultra-wide-angle lens for the Contarex system, manufactured by Carl Zeiss Oberkochen.
It is a legendary lens, also renowned for its performance on the Contax IIa/IIIa.
Introduced in 1959, it remained in production until 1962.
This particular example, with a serial number in the 3,250,000 range, was manufactured in 1964.
A total of 4,000 units were produced.
The measured weight is 270g.
It features a symmetrical design with 8 elements in 5 groups.
As it is a non-retrofocus lens, the rear element protrudes significantly.
When shooting, mirror lock-up is required, and focusing is done by estimation.
A dedicated viewfinder is mounted onto the Contarex's accessory shoe for framing.
The minimum focusing distance is 2 feet, or approximately 60 cm.

The lens is in exceptionally beautiful condition, with the plating retaining its original luster and maintaining a superb appearance.
The included hood is also in excellent condition.
Fully overhauled in April 2025, the aperture and helicoid now operate with smooth precision.
The haze on the glass has been removed, resulting in a clean, clear view, and no notable scratches are present — the optics are in excellent condition.
The lens comes with its original front cap, hood, and a plastic case.
The hood is compatible with lenses from 21mm to 35mm.
This is a Biogon for the Contarex system, well suited for both use and collection!