Overview

The Carl Zeiss Jena R-Biotar 100mm f/0.73 is an extremely fast lens requiring significant camera modification (removing the sensor, reducing flange distance to 4mm) to achieve infinity focus. Its optical performance is demonstrated in real-world tests, but practical use is limited. The lens suits bokeh and low-light enthusiasts willing to modify their gear, though similar results may be achievable with modern sensors and speed boosters. Build and handling are not discussed in detail, but the modification process is described as 'painful'.