Exposure device, LED head, image forming apparatus, and reading apparatus

An LED (Light Emitting Diode) head comprising:

• an LED array formed of a plurality of LED elements, said LED elements being arranged substantially linearly with a specific interval PD in between;
• and
• a lens array including a plurality of lens assembly members and at least one light blocking member, said lens assembly members being arranged substantially in parallel to the LED array, said light blocking member being arranged between the lens assembly member, each of said lens assembly members including a plurality of lenses arranged in a direction perpendicular to optical axes thereof so that the optical axes of the lenses are aligned with those of lenses of an adjacent lens assembly member arranged to face the lenses, said light blocking member including a plurality of apertures arranged such that an optical axis of a pair of the lenses of two adjacent lens assembly members facing each other passes through each of the apertures, said LED array and said lens array being arranged so that when light in parallel to the optical axis of one of the lenses is incident to the one of the lenses from a direction of the light blocking member, the one of the lenses forms a spot having a radius RS satisfying the following relationship:
• RS
• <
• PD
• ·
• FO
• 2
• 
• LO
• where FO is a focal length of the one of the lenses, LO is a distance between the one of the lenses and the LED array, and FO is a distance between the one of the lenses and a plane where the spot is formed on a side of the LED elements.

A reading apparatus comprising:

• a line sensor formed of a plurality of light receiving elements, said light receiving elements being arranged substantially linearly with a specific interval PR in between;
• and
• a lens array including a plurality of lens assembly members and at least one light blocking member, said lens assembly members being arranged substantially in parallel to the line sensor, said light blocking member being arranged between the lens assembly member, each of said lens assembly members including a plurality of lenses arranged in a direction perpendicular to optical axes thereof so that the optical axes of the lenses are aligned with those of lenses of an adjacent lens assembly member arranged to face the lenses, said light blocking member including a plurality of apertures arranged such that an optical axis of a pair of the lenses of two adjacent lens assembly members facing each other passes through each of the apertures, said line sensor and said lens array being arranged so that when light in parallel to the optical axis of one of the lenses is incident to the one of the lenses from a direction of the light blocking member, the one of the lenses forms a spot having a radius RS satisfying the following relationship:
• RS
• <
• PR
• ·
• FO
• 2
• 
• LO
• where FO is a focal length of the one of the lenses, LO is a distance between the one of the lenses and the line sensor, and FO is a distance between the one of the lenses and a plane where the spot is formed on a side of the light receiving elements.