Lens unit, exposure device, LED head, image forming apparatus, and scanning device

A lens unit comprising:

• a first lens array including a plurality of first lenses arranged in at least two parallel first lines extending in a first direction;
• a second lens array including a plurality of second lenses arranged in correspondence with the first lens array, the plurality of second lenses respectively facing the plurality of first lenses of the first lens array, the second lens array being arranged to face the first lens array so that each pair of the first and second lenses facing each other has a common optical axis;
• a first light blocking member arranged between the first lens array and the second lens array and having a plurality of first openings arranged in at least two parallel second lines extending in the first direction, the plurality of first openings each being arranged to face the pair of the first and second lenses in a direction of the optical axis;
• and
• a second light blocking member arranged to face the first light blocking member via the second lens array and having a plurality of second openings, each of the plurality of second openings being situated at a focal position of a corresponding second lens of the second lens array and being arranged to face a respective pair of the first and second lenses in the direction of the optical axis, wherein
• PXL is defined as a distance in a second direction orthogonal to the first direction and the direction of the optical axis, between a first passing line passing in the first direction through an array center position that is a center between two adjacent first lines of the at least two first lines and a second passing line passing in the first direction through the optical axis of any one of the first lenses,
• PXS is defined as a distance in the second direction between a third passing line passing in the direction of the optical axis, through the array center position and a fourth passing line passing in the direction of the optical axis, through an opening center of any one of the first openings, and
• the PXL and the PXS satisfy a relationship of
• PXS·(m−1)/m<PXL<PXS
• where m represents a ratio of a distance from a first principal surface of the second lens to an object surface to a focal length of the second lens.