First we can look into the appearance of the camera. Normally the dimension of camera with fix lens is less than camera with vari-focal lens. Meanwhile the vari-focal camera has auxiliary components, such as iris control, motor, gear. Secondly we can refer to specification of lens. Generally the focal length of fixed camera is a fix value, shown in the picture below: ItemsDescriptionTolerances Focal Length3.6mm±5% Aperture (D/f)F2.0±5% Image Circle1/2.7">6.9mm Focus Range0.3m~INF While the focal length of the vari-focal camera is a range of value, shown in the picture below: ItemsDescriptionTolerances F No.1.5±5% Focal Length3.6-11mm±5% Optical Back Focal Length6.24mm (In Air)±0.1 Mechanical Back Focal Length13.20mm (In Air)±0.1 Image Circle9