A surface height and focus sensing system is provided. In one embodiment, an illumination focus sensor is used in combination with a collimation adjustment element which drives the system such that an illumination focus height matches the workpiece surface height, which produces a null output from the illumination focus sensor. Under the null condition, the amount of collimation adjustment is directly related to the workpiece surface height, and the resulting height determination is relatively insensitive to the workpiece surface optical properties. In one embodiment, the amount of collimation adjustment is determined according to the control signal for the collimation adjustment element. In another embodiment, a collimation adjustment sensor is utilized to measure the amount of collimation adjustment.