Automatic focusing apparatus.

摘要

An automatic focusing apparatus is constructed of a base (21) on which a substrate (10) is placed, detection means (5) for detecting a pressure of air which is caused to flow out of an interspace between the substrate (10) and an orifice (6) by spurting the air from the orifice (6) toward the substrate (10), reference pressure generation means for generating a reference pressure (8) which is necessary for setting a standard distance between the substrate (10) and the orifice (6), a pressure transducer (11) which receives pressure signals from said detection means (5) and said reference pressure generation means (8) and which converts a pressure difference between these pressure signals into an electric signal, base drive means (14) for moving the substrate (10) in parallel with the orifice (6) on the basis of the output signals from said pressure transducer (11), and offset signal generation means (19) for generating a signal which, when superposed on the output signal from said pressure transducer, serves to shift the substrate (10) from the standard distance.