Optical system for copier

Claim 2

An optical system for use in a copier comprising: a halogen lamp; a CdS photosensitive member; and a reflective projection lens system comprising a lens and a reflective surface, including a multi-layered interference coating formed on a substrate, provided behind said lens, said interference coating being a 5- to 9- layered structure composed of alternately superposed high refractive layers and low-refractive layers each of a basic optical thickness equal to 1/4 of a design wavelength λ 0 and including therein two and one adjusting layers at the substrate side and the air side, respectively, of said coating to prevent reflection in the near-infrared wavelength region to thereby match the spectral characteristics of the light reflected from an original with the spectral sensitivity of said photosensitive member, wherein the optical thickness ND i of an i-th layer counted from the substrate side satisfies the following relation: ND.sub.n <ND.sub.1 <ND.sub.2 <ND.sub.3 = . . . =ND.sub.n-1.

Claim 3

An optical system for use in a copier according to claim 1 wherein said multi-layered interference coating is a 5-, 7- or 9-layered structure starting with a high-refractive layer provided on the substrate.

Claim 4

An optical system for use in a copier according to claim 1 wherein said multi-layered interference coating has the following composition: ______________________________________ Refractive index Thickness ND/λ.sub.0 ______________________________________ Substrate 1.52 Layer 1 2.13 0.150 2 1.38 0.202 3 2.13 0.250 4 1.38 0.250 5 2.13 0.250 6 1.38 0.250 7 2.13 0.126 Air 1.00 ______________________________________

Claim 5

An optical system for use in a copier according to claim 1 wherein said multi-layered interference coating has the following composition: ______________________________________ Refractive index Thickness ND/λ.sub.0 ______________________________________ Substrate 1.52 Layer 1 2.05 0.104 2 1.38 0.250 3 2.05 0.250 4 1.38 0.250 5 2.05 0.250 6 1.38 0.250 7 2.05 0.250 8 1.38 0.357 9 2.05 0.079 Air 1.00 ______________________________________

Claim 6

An optical system for use in a copier according to claim 1 wherein said multi-layered interference coating following composition: ______________________________________ Refractive index Thickness ND/λ.sub.0 ______________________________________ Substrate 1.52 Layer 1 2.35 0.134 2 1.38 0.145 3 2.35 0.250 4 1.38 0.250 5 2.35 0.083 Air 1.00 ______________________________________

Claim 7

An optical system for use in a copier according to claim 1, wherein said substrate is a glass substrate.

Claim 8

An optical system for use in a copier according to claim 6, wherein a matted surface is provided on a rear surface of said glass substrate and a light-absorbing anti-reflective layer is provided on said matted surface.

Claim 9

An optical system for use in a copier comprising: a halogen lamp; a CdS photosensitive member; and a reflective projection lens system comprising a lens and a reflective surface, including a multi-layered interference coating formed on a substrate, provided behind said lens, said interference coating being a 5- to 9-layered structure composed of alternately superposed high-refractive layers and low-refractive layers each of a basic optical thickness equal to 1/4 of a design wavelength λ 0 and including therein one and two adjusting layers at the substrate side and the air side of said coating, respectively, to prevent reflection in the near-infrared wave-length region to thereby match the spectral characteristics of the light reflected from an original with the spectral sensitivity of said photosensitive member, wherein the optical thickness ND i of an i-th layer counted from the substrate side satisfies the following relation: ND.sub.n <ND.sub.1 <ND.sub.2 . . . =ND.sub.n-2 <ND.sub.n-1.

Claim 10

An optical system for use in a copier comprising: a halogen lamp; a CdS photosensitive member; and a reflective projection lens system comprising a lens and a reflective surface, including a multi-layered interference coating formed on a substrate, provided behind said lens, said interference coating being a 5- to 9-layered structure composed of alternately superposed high-refractive layers and low-refractive layers each of a basic optical thickness equal to 1/4 of a design wavelength λ 0 and including therein one and two adjusting layers at the substrate side and the air side of said coating, respectively, to prevent reflection in the near-infrared wave-length region to thereby match the spectral characteristics of the light reflected from an original with the spectral sensitivity of said photosensitive member, wherein the optical thickness ND i of an i-th layer counted from the substrate side satisfies the following relation: ND.sub.n <ND.sub.1 <ND.sub.2 . . . =ND.sub.n-2 <ND.sub.n-1.

Claim 11

An optical system for use in a copier according to claim 8 wherein said multi-layered interference coating has the following composition: ______________________________________ Refractive index Thickness ND/λ.sub.0 ______________________________________ Substrate 1.52 Layer 1 2.15 0.125 2 1.38 0.250 3 2.15 0.250 4 1.38 0.250 5 2.15 0.250 6 1.38 0.360 7 2.15 0.100 Air 1.00 ______________________________________

Claim 12

An optical system for use in a copier according to claim 8 wherein said multi-layered interference coating is a 5-, 7- or 9- layered structure starting with a high-refractive layer provided on the substrate.

Claim 13

An optical system for use in a copier according to claim 8, wherein said substrate is a glass substrate.

Claim 14

An optical system for use in a copier according to claim 11, wherein a matted surface is provided on the rear surface of said glass substrate and a light-absorbing anti-reflective layer is provided on said matted surface.