The shaft diameter of the flexible cystoscope lies between 16 and 20 CH, flexible glass fibres aid the transportation of light and image information. The distal end of the cystoscope can actively be controlled, on correct handling with the thumb. Light performance and optical quality are inferior compared to the rigid instruments; likewise, it has less mechanical robustness.
Source of picture and further information: http://www.urologielehrbuch.de/zystoskopie.html