Evaluating method of lens array, evaluating apparatus of lens array, manufacturing method of optical apparatus, and manufacturing method of image forming apparatus

An apparatus for evaluating a lens array, comprising:

• a light source unit configured to emit measurement light;
• a light receiving unit configured to receive the measurement light;
• a driving unit configured to move at least one of the light source unit, the light receiving unit, and the lens array including a plurality of lens portions;
• and
• a controller,
• wherein the controller is configured to perform:
• moving at least one of the light source unit, the light receiving unit, and the lens array in a first plane perpendicular to an optical axis direction such that at least one lens portion of the plurality of lens portions intersects an optical path of the measurement light from the light source unit by the driving unit;
• causing the light receiving unit to receive the measurement light having passed through a predetermined lens portion of the at least one lens portion at a plurality of timings in the moving;
• calculating a gradient at each position in a positional dependence of a light amount of the measurement light for the at least one lens portion received by the light receiving unit in the causing from time dependence of the light amount;
• and
• evaluating the lens array based on information obtained in the calculating.