A lens mount adapter made by Cook & Perkins of the UK.
This example appears to be the so-called Series 1 type, designed to convert 50mm internal bayonet mount lenses for Contax rangefinder cameras to Leica L mount.
It features rangefinder coupling and a chrome finish. Naturally, the distance scale is in feet. The minimum focusing distance is 3.5 feet (1 meter).

There has long been demand to use excellent Contax-mount Sonnar and Tessar lenses on Leica bodies, and to our knowledge, this Cook & Perkins adapter was the first commercially produced mount conversion adapter to fulfill that need.
This makes it a historically significant piece, highly prized among collectors for decades.

Despite its historical reputation, the adapter is rarely seen today.
It is believed that only a small number were produced from the prewar through postwar periods. Several design variations exist — in addition to this internal bayonet version, there are models that accommodate external bayonet mounts as well.
Adapters have been documented up through Series 3A.

This particular unit is thought to date from the 1940s to 1950s and features a chrome finish reminiscent of the British-made Leica copy Reid III, with which it shares a similar aesthetic quality.

Shows very little sign of use and remains in excellent cosmetic condition, preserving the feel of a vintage piece in near-new condition.

Fully overhauled in May 2025.
The helicoid action has been finely tuned for smooth operation; however, due to the structural design, the rangefinder coupling cam is rather thick, which results in some resistance when mounted on a camera — the focusing feel is slightly heavy.

Mounting and shooting tests were performed using Contax-mount Sonnar and Tessar lenses.
Rangefinder coupling is accurate at close distances. From around 5 meters to infinity, there is a very slight front-focus tendency, but stopping down by just one stop brings the subject comfortably into the depth of field.

Due to the adapter’s overall delicate construction, please avoid applying excessive force when mounting or removing lenses or the adapter itself — doing so may risk distorting the adapter.

This historically important accessory likely served as the design reference for later adapters such as the Orion ring.
A rare and collectible item.