Method and apparatus for determining focus conditions

Abstract

Focus accuracy of a radiant energy recording beam is determined by recording test signals along a spiral track to form on the recording medium a series of adjacent bands. Each band comprises a plurality of track convolutions. Track convolutions in each band are recorded at a focus setting on the recording beam which is different by known increments from the focus setting of the beam when track convolutions in respective bands adjacent thereto are recorded. The best focus conditions are obtained at the focus setting of the recording beam forming the brightest band. By comparing the position of that band relative to the position of the band formed by the recording beam at the focus setting at which information is recorded, an accurate determination of the focus conditions thereat is readily obtained from the known increments of focus settings.