The Planar 50mm f/2 is a standard lens for the Contarex system, manufactured by Carl Zeiss in Germany.
This particular example is the early white barrel version, originally supplied as the standard lens for the Contarex Bullseye.
Introduced in 1958, a total of 37,768 units were produced through 1973.
It features an optical construction of 6 elements in 4 groups.
The minimum focusing distance is approximately 30 cm, allowing for relatively close-up shooting.
The measured weight is 239g, making it relatively lightweight.
Later versions of this lens feature a black barrel and, from 1965 onward, an integrated flashmatic system.

The lens shows almost no signs of use and has a very clean appearance.
The helicoid, aperture, and other mechanisms operate smoothly and reliably.
There is a slight amount of dust inside the lens elements, and under strong LED light, a faint whitish coating deterioration can be seen on the surface of the rear element.
However, neither is expected to affect actual shooting performance.
The lens comes with a well-made original hood designed for 50mm to 135mm lenses (with its case) and a plastic storage case.