Imaging system, writing head, and image forming apparatus

1. An imaging system, comprising:

a plurality of incidence faces composed of a plurality of optical faces through which light enters and having an image focusing function;

a plurality of prisms; and

a plurality of exit faces,

wherein the plurality of incidence faces is arranged with a first pitch along a first axial direction, the plurality of prisms is arranged with a second pitch along the first axial direction, the plurality of the exit faces is arranged with a third pitch along the first axial direction,

wherein the first axial direction is set as a Y direction,

wherein a normal line direction of a face top of an optical face of the incidence face in a plane perpendicular to the first axial direction is set as a X direction,

wherein a direction perpendicular to the Y direction and the X direction is set as a Z direction, and

wherein in a XZ cross-section plane, a width of the prism in the Z direction is smaller than a width of the optical face of the incidence face in the Z direction.

2. The imaging system of claim 1 , wherein the second pitch is shorter than the first pitch and the third pitch.

3. The imaging system of claim 1 , wherein in the XZ cross-section plane, a width of the prism in the X direction is smaller than a width of optical face of the exit face in the X direction.

4. The imaging system of claim 1 , wherein a part of light emitted from a point light source and passing the incidence face does not enter the prism.

5. The imaging system of claim 4 , wherein the light not entering the prism exits outside the imaging system from a part of a face connecting the prism and the exit face.

6. The imaging system of claim 5 , wherein in the XZ cross-section plane, the X direction from the incidence face toward the prism is set as a positive direction, the Z direction from the prism toward the exit face is set as a positive direction, and an angle from the X direction to the Z direction is set as a positive angle,

wherein among side faces connected to the prism, an angle θ1 defined by a side face connected to the incidence face and the positive X direction satisfies a first condition: −90 deg≦θ1<0 deg.

7. The imaging system of claim 5 , wherein in the XZ cross-section plane, the X direction from the incidence face toward the prism is set as a positive direction, the Z direction from the prism toward the exit face is set as a a positive direction, and an angle from the X direction to the Z direction is set as a positive angle,

wherein among side faces connected to the prism, an angle θ2 defined by a side face connected to the exit face and the positive X direction satisfies a second condition: −90 deg≦θ2<0 deg.

8. The imaging system of claim 5 , wherein in the XZ cross-section plane, the X direction from the incidence face toward the prism is set as a positive direction, the Z direction from the prism toward the exit face is set as a positive direction, and an angle from the X direction to the Z direction is set as a positive angle,

wherein a light path of light passing through a portion of the incidence face but not entering the prism and entering a side face connecting the prism and the exit face,

wherein a normal line of the side face, connecting the prism and the exit face, and a line parallel to the positive X direction axis intersect at one point, wherein an angle θ3 defined by the normal line of the side face, connecting the prism and the exit face, and the line parallel to the positive X direction axis satisfies a third condition: −40 deg≦θ3<90 deg.

9. The imaging system of claim 8 , wherein the angle θ 3 further satisfies a fourth condition: 0 deg<θ3<90 deg.

10. The imaging system of claim 1 , wherein light emitted from a light source enters a plurality of optical faces of the incidence face, exits from the plurality of optical faces of the exit face, and is then focused at a substantially one point.

11. The imaging system of claim 1 , wherein one optical face of the incidence face and one optical face of the exit face existing at the same position with respect to the first axial direction are paired,

wherein a virtual plane connects an end of the paired optical face of the incidence face in the first axial direction and an end of the paired optical face of the exit face in the first axial direction,

wherein among light emitted from a point light source and entering the paired optical face of the incidence face, light passing through the virtual plane is reflected by the prism, and then passing through the virtual plane again, and then going to the paired optical face of the exit face.

12. A writing head, comprising:

a light source array having a plurality of light sources arranged in at least one line pattern;

a board to retain the light source array; and

the imaging system of claim 1 to which light from the light source array enters.

13. An image forming apparatus, comprising:

the writing head of claim 12 ;

an image bearing member;

a development unit to develop an electrostatic latent image formed on the image bearing member as a toner image by the writing head using each color of toner; and

a transfer unit to transfer the toner image developed on the image bearing member to a recording medium.