The employment of optics that effectively utilizes a high NA objective lens results in improved height measurement accuracy and powerful measurement ability on inclined plane.

A real-time compensation mode for saturated signal from very bright surface and very week signal from dark surface is developed. For example, in a case that such materials like solder of high reflectivity is on a substrate of low reflectivity, picture information level at the solder/substrate boundary is intrinsically low and difficult to see the image. This new mode produce clear image even from data submerging as dark area.

The lens NA (aperture ratio), an important factor for determining performance of objective lens, is raised by a specific design. Higher performance such as NA 0.25 for 5X, 0.50 for 10X and 0.75 for 20X is obtained, respectively. Especially for a 5X objective lens, the pupil diameter is made to be 20 mm and the resulting incident light angle at the outermost circumference is 14.5 degrees with diametric view of 3.6 mm, which raises condensing rate of reflective light. For this reason, images can be acquired with high brightness even under low magnification and high precision measurement with low level of noise from inclined plane is available at the time of measurement.