Abstract: In a position detecting apparatus, according to this invention, a convexly and concavely patterned wafer mark is imaged on an image pickup surface via an imaging optical system, and the image on the image pickup surface is detected. The position detecting apparatus defocuses the average surface of the wafer mark from the optimum focusing surface depending on the pitch and difference in level of the wafer mark, etc., in the direction of the optical axis of the imaging optical system, and varies an illumination .sigma. value definded as the ratio of the numerical aperture of the illumination optical system and the numerical aperture of the imaging optical system. Then the position detecting apparatus provides lights from the wafer mark to the image pickup surface with rotation-symmetric wave aberration to allow the resulting image to have the highest contrast for positional detection.

Abstract: A distance measuring apparatus comprises light emitting means for projecting light; light receiving means for receiving light; arithmetic means for performing arithmetic operation based on signals from the light receiving means; integrating means having an integrating capacitor, for integrating signals from the arithmetic means by discharging the integrating capacitor; detecting means for detecting distance based on signals from the integrating means; and charging means for performing preliminary charge of the integrating capacitor before the distance measurement is carried out. The present invention prevents voltage drop due to dielectric absorption of the integrating capacitor, thereby to solve problems of distance measurement error due to the voltage drop.