"Sample fraction" usually refers to the fraction of a circle monitored, as the angle of view of the camera in degrees / 360 (theta). It can be included in the calculation of point-specific effort as describe in Howe et al. 2017, or, if theta is the same for all cameras, as the sample fraction multiplier. Activity level, estimated as described by Eric R, can also be included as a "multiplier", but isn't usually referred to as the sample fraction multiplier. "Sample fraction" usually refers to situations where < a complete circle is monitored.