Chinese companies Funleader and Mr. Ding have introduced a new conversion kit designed to adapt the Contax G 28mm f/2.8 Zeiss Biogon T* lens for use on Leica M-mount rangefinder cameras. The project extends an ongoing effort to make Contax G lenses compatible with Leica systems without permanently modifying the original optics.

The Contax G system, developed in the 1990s through a collaboration between Contax and Zeiss, was one of the few rangefinder systems to incorporate autofocus. While the original camera bodies are no longer widely used, the lenses remain in demand due to their optical performance and characteristic rendering. Adapting these lenses to Leica M cameras presents a technical challenge, as the Contax G mount relies on an autofocus mechanism rather than the mechanical rangefinder coupling required by Leica systems.

The conversion kit addresses this by replacing the original autofocus helicoid with a mechanically coupled focusing system compatible with Leica M bodies. The process involves disassembling the lens and installing its optical unit into a dedicated helicoid assembly provided in the kit. The design does not alter the optical formula or permanently modify the original components, allowing the lens to be restored to its original configuration if needed.

Construction of the kit also combines a brass internal structure with an aluminum exterior, thus maintaining mechanical precision while limiting overall weight. The adapter supports rangefinder-coupled focusing and is designed to replicate the handling characteristics expected from native Leica M lenses.