Cannon 9721-F53 Model CFOC-50 Size 50 Cannon-Fenske Opaque Viscometer Tube, Calibrated. The Cannon-Fenske Opaque Viscometer measures kinematic viscosity of transparent and opaque Newtonian liquids according to ASTM D445, ISO 3104 and ASTM D2170. Minimum sample volume is 12 mL. Minimum bath depth is 230 mm (9 in). These viscometers include a certificate of calibration and instruction sheet. Holders are sold separately.