Device for detecting the levelling of the surface of an object

A device for detecting the levelling of an object disposed on a plane substantially perpendicular to the optic axis of main objective optical means, comprising:

• a first levelling detection system having a first irradiating optical system for supplying a collimated first light beam to a particular area of the surface said object from a direction oblique relative to the optic axis of said main objective optical means, and a first condensing optical system for condensing on first light receiving means the first light beam supplied from said first irradiating optical system and reflected by said particular area, the optic axis of said first irradiating optical system and the optic axis of said first condensing optical system being disposed symmetrically with respect to the optic axis of said main objective optical means, said first levelling detection system detecting the inclination of said particular area relative to a reference plane with respect to a first direction on said reference plane;
• a second levelling detection system having a second irradiating optical system for supplying a collimated second light beam to said particular area from a direction oblique relative to the optic axis of said main objective optical means, and a second condensing optical system for condensing on second light receiving means the second light beam supplied from said second irradiating optical system and reflected by said particular area, the optic axis of said second irradiating optical system and the optic axis of said second condensing optical system being disposed symmetrically with respect to the optic axis of said main objective optical means, said second levelling detection system detecting the inclination of said particular area relative to said reference plane with respect to a second direction on said reference plane differing from said first direction;
• and
• means for determining the levelling of said reference plane on the basis of the inclination of said first direction and the inclination of said second direction.