Optical scanning device in image forming apparatus, and control method thereof

An optical scanning device which forms a plurality of scanning lines on a photosensitive member, comprising:

• a plurality of light sources configured to emit m light beams for exposing different positions on one photosensitive member in a rotation direction of the one photosensitive member;
• a deflection unit configured to deflect the m light beams such that the m light beams scan the photosensitive member in a main-scanning direction;
• a lens through which the m deflected light beams pass;
• a curvature detection unit configured to detect n first curvatures of n (n<m) first light beams in the m light beams in a sub-scanning direction orthogonal to the main-scanning direction, and to determine n first equations representing the n first curvatures of the n first light beams based on the detected n first curvatures;
• an interpolating unit configured to interpolate using the n first equations to obtain (m−n) second equations representing (m−n) second curvatures of (m−n) second light beams other than the n first light beams in the m light beams;
• and
• a calculating unit configured to calculate n first correction data of the n first light beams based on the n first equations and (m−n) second correction data of the (m−n) second light beams based on the (m−n) second equations.