Carl Zeiss Biogon T* 21mm 2/8 with GF-21mm Finder. For use with Contax G serie

The Carl Zeiss Biogon T 21mm f/2.8* is a legendary ultra-wide-angle lens designed for the autofocus Contax G rangefinder system. It is highly regarded for its symmetrical Biogon optical design, which provides near-zero distortion and exceptional corner-to-corner sharpness. Because the built-in viewfinders of the Contax G1 and G2 cannot display a 21mm field of view, this lens originally shipped with the external Contax GVF-21 optical viewfinder that mounts onto the camera’s hot shoe.

Specs

Focal length: 21 mm

Maximum aperture: f/2.8

Minimum aperture: f/22

Lens construction: 9 elements in 7 groups

Lens coating: Carl Zeiss T* multi-coating (for flare reduction and high contrast)

Angle of view: 90° (diagonal on 35mm full-frame)

Aperture blades: 7 blades

Minimum focus distance: 0.5 meters (1.64 feet)

Focusing: Autofocus (driven by the physical coupling motor inside the camera body)

Filter size: 55 mm (screw-in type)

Dimensions: 58 mm x 33.5 mm (diameter x length)

Weight: 190 grams (6.7 oz)

Camera Compatibility & Mirrorless Adapting

Contax G2: Fully compatible.

Contax G1: Only compatible with “Green Label” modified bodies. The original silver-label G1 requires a ROM update to focus this lens.

Digital Mirrorless: Highly popular for adapting to modern cameras (Sony E, Leica M, Fujifilm X) via manual or autofocus adapters (like Techart).

Sensor Note: Because the rear element sits very close to the sensor, it can cause colour shifting (shading) and corner smearing on certain digital sensors without microlens optimization.