Abstract: A rod lens array 10a includes a plurality of gradient-index rod lenses 1b arrayed to have optical axes parallel to each other, and forms an erecting equal-magnification image. The gradient-index rod lenses 1b each have a refractive-index distribution in a radial direction thereof. The refractive-index distribution n(r) is approximated by n(r)=n0?{1-(A/2)?r2}, where a refractive index at a center of the gradient-index rod lens 1b is represented by n0, a refractive-index distribution constant of the gradient-index rod lens 1b is represented by \A, and a distance from the center of the gradient-index rod lens 1b is represented by r. The gradient-index rod lens 1b has an aperture angle ? of 3 to 6°, the aperture angle ? represented by ?=sin?1(n0\A?r0), where a radius of the gradient-index rod lens is represented by r0. The rod lens array 10a has an imaging distance of 45 to 75 mm and a depth of field of 1.5 to 3.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 nm to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, and 40°, the optical filter (1a) satisfies given transmittance requirements. IE?1/?2?1 to ?2, IAE?1/?2?1 to ?2, and ISE?1/?2?1 to ?2 defined by the following equations (1) to (3) for two incident angles ?1° and ?2° (?1<?2) selected from 0°, 30°, and 40° satisfy given requirements in a given domain of a wavelength ?.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 nm to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, and 40°, the optical filter (1a) satisfies given transmittance requirements. Nine differences each obtained as a difference between one and another of IE?xR, IE?yG, and IE?zB defined for incident angles ?° of 0°, 30°, and 40° satisfy given requirements, and ranges satisfy given requirements, each range being a difference obtained by subtracting the smallest value of three differences from the largest value of the three differences, the three differences obtained from IE?xR, IE?yG, and IE?zB collectively defined for the same pair selected from the incident angles ?°.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at an incident angle of 0°, the optical filter (1a) satisfies given requirements. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, 35°, and 40°, the optical filter (1a) satisfies given requirements related to a normalized spectral transmittance. The normalized spectral transmittance is determined by normalization of a spectral transmittance for each incident angle so that the maximum of the spectral transmittance for each incident angle in the wavelength range of 400 to 650 nm is 100%.

Abstract: An optical (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at an incident angle of 0°, the optical filter (1a) satisfies given spectral transmittance requirements. When an average of absolute values of differences each between a value of a normalized spectral transmittance for an incident angle x° and a value of a normalized spectral transmittance for an incident angle y° in the wavelength range of W nm to V nm (W<V) is expressed as ?TSx/yW-V, the optical filter (1a) satisfies requirements ?TS0/40380-530?3%, ?TS0/40450-650?3%, and ?TS0/40530-750?3%.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 nm to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, and 40°, the optical filter (1a) satisfies given transmittance requirements. IE?1/?2CR, IE?1/?2CG, and IE?1/?2CB defined for two incident angles ?1° and ?2° (?1<?2) selected from 0°, 30°, and 40° satisfy given requirements. Ranges satisfy given requirements, each range being a difference obtained by subtracting the smallest value of IE?1/?2CR, IE?1/?2CG, and IE?1/?2CB defined for the same two incident angles ?1° and ?2° from the largest value of IE?1/?2CR, IE?1/?2CG, and IE?1/?2CB defined for the same two incident angles ?1° and ?2°.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at an incident angle of 0°, the optical filter (1a) satisfies given requirements. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, 35°, and 40°, the optical filter (1a) satisfies given requirements related to a normalized spectral transmittance. The normalized spectral transmittance is determined by normalization of a spectral transmittance for each incident angle so that the maximum of the spectral transmittance for each incident angle in the wavelength range of 400 to 650 nm is 100%.

Abstract: An optical (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 to 1200 nm is incident on the optical filter (1a) at an incident angle of 0°, the optical filter (1a) satisfies given spectral transmittance requirements. When an average of absolute values of differences each between a value of a normalized spectral transmittance for an incident angle x° and a value of a normalized spectral transmittance for an incident angle y° in the wavelength range of W nm to V nm (W<V) is expressed as ?TSSx/yW-V, the optical filter (1a) satisfies requirements ?TS0/40380-530?3%, ?TS0/40450-650?3%, and ?TS0/40530-750?3%.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 nm to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, and 40°, the optical filter (1a) satisfies given transmittance requirements. IE?1/?2CR, IE?1/?2CG, and IE?1/?2CB defined for two incident angles ?1° and ?2° (?1<?2) selected from 0°, 30°, and 40° satisfy given requirements. Ranges satisfy given requirements, each range being a difference obtained by subtracting the smallest value of IE?1/?2CR, IE?1/?2CG, and IE?1/?2CB defined for the same two incident angles ?1° and ?2° from the largest value of IE?1/?2CR, IE?1/?2CG, and IE?1/?2CB defined for the same two incident angles ?1° and ?2°.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 nm to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, and 40°, the optical filter (1a) satisfies given transmittance requirements. IE?1/?2?1 to ?2, IAE?1/?2?1 to ?2, and ISE?1/?2?1 to ?2 defined by the following equations (1) to (3) for two incident angles ?1° and ?2° (?1<?2) selected from 0°, 30°, and 40° satisfy given requirements in a given domain of a wavelength ?.

Abstract: An optical filter (1a) includes a light-absorbing layer (10). The light-absorbing layer absorbs light in at least a portion of the near-infrared region. When light with a wavelength of 300 nm to 1200 nm is incident on the optical filter (1a) at incident angles of 0°, 30°, and 40°, the optical filter (1a) satisfies given transmittance requirements. Nine differences each obtained as a difference between one and another of IE0xR, IE?yG, and IE?zB defined for incident angles ?° of 0°, 30°, and 40° satisfy given requirements, and ranges satisfy given requirements, each range being a difference obtained by subtracting the smallest value of three differences from the largest value of the three differences, the three differences obtained from IE?xR, IE?yG, and IE?zB collectively defined for the same pair selected from the incident angles ?°.

Abstract: Disclosed is an image forming apparatus which provides an image of an excellent quality which has a less variation in resolution and suppressed linear irregularity. A rod lens array includes two rows of rod lenses stacked one on the other. An LED array is offset by a predetermined offset amount from a plane passing the median position between the first row of rod lenses and the second row of rod lenses. This structure can realize an LED printer head which reduces a variation in the resolution of the rod lens array, thereby suppressing linear irregularity, and can thus provide an image having an excellent quality.

Abstract: An optical write-in head for obtaining a clear image even in printing at a relatively high recording density without generating strip-like irregularities in most cases. The optical write-in head applies light carrying image information to a photosensitive substance. The optical write-in head includes an array light source having a plurality of dot light sources each of which selectively emits the light corresponding to the image information, and a lens array facing the array light source. The lens array has a plurality of lens elements which corresponds to the plurality of dot light sources respectively. An angular aperture ? of each of the lens elements is set in a range of about 14° to 18°.

Abstract: Disclosed is an image forming apparatus which provides an image of an excellent quality which has a less variation in resolution and suppressed linear irregularity. A rod lens array includes two rows of rod lenses stacked one on the other. An LED array is offset by a predetermined offset amount from a plane passing the median position between the first row of rod lenses and the second row of rod lenses. This structure can realize an LED printer head which reduces a variation in the resolution of the rod lens array, thereby suppressing linear irregularity, and can thus provide an image having an excellent quality.

Abstract: An optical write-in head for obtaining a clear image even in printing at a relatively high recording density without generating strip-like irregularities in most cases. The optical write-in head applies light carrying image information to a photosensitive substance. The optical write-in head includes an array light source having a plurality of dot light sources, each of which selectively emits the light corresponding to the image information, and a lens array facing the array light source. The lens array has a plurality of lens elements which corresponds to the plurality of dot light sources respectively. An angular aperture ? of each of the lens elements is set in a range of about 14° to 18°.

Abstract: An optical write-in head for obtaining a clear image even in printing at a relatively high recording density without generating strip-like irregularities in most cases. The optical write-in head applies light carrying image information to a photosensitive substance. The optical write-in head includes an array light source having a plurality of dot light sources each of which selectively emits the light corresponding to the image information, and a lens array facing the array light source. The lens array has a plurality of lens elements which corresponds to the plurality of dot light sources respectively. An angular aperture &thgr; of each of the lens elements is set in a range of about 14° to 18°.

Abstract: Disclosed is an image forming apparatus which provides an image of an excellent quality which has a less variation in resolution and suppressed linear irregularity. A rod lens array includes two rows of rod lenses stacked one on the other. An LED array is offset by a predetermined offset amount from a plane passing the median position between the first row of rod lenses and the second row of rod lenses. This structure can realize an LED printer head which reduces a variation in the resolution of the rod lens array, thereby suppressing linear irregularity, and can thus provide an image having an excellent quality.

Abstract: An optical write-in head for obtaining a clear image even in printing at a relatively high recording density without generating strip-like irregularities in most cases. The optical write-in head applies light carrying image information to a photosensitive substance. The optical write-in head includes an array light source having a plurality of dot light sources, each of which selectively emits the light corresponding to the image information, and a lens array facing the array light source. The lens array has a plurality of lens elements which corresponds to the plurality of dot light sources respectively. An angular aperture &thgr; of each of the lens elements is set in a range of about 14° to 18°.