Telecentric f-theta lens system

Claim 2

A telecentric f-ϑ lens system comprising: (a) a first lens group (FL) having an entrance pupil (EP), characterised in that the first lens group includes: (a-1) a first meniscus lens (L₁) having a positive power, said first lens (L₁) having a concave surface (S₁) which is directed towards said entrance pupil (EP), (a-2) a second lens (L₂) having a negative power, (a-3) third and fourth meniscus lenses (L₃,L₄) each having a positive power, respectively; and (b) a second lens group (RL) including a fifth lens (L₅) having a positive power, said first through fifth lenses (L₁-L₅) being successively disposed in order from said entrance pupil (EP).

Claim 3

A telecentric f-ϑ lens system according to Claim 1, wherein said telecentric f-ϑ lens system satisfies the following: -0.65 < (r₁/f) < -0.25 0.4 < (d₈/f) < 1.16 1.61 < (f₅/f) < 3.5 where r₁ the radius of curvature of said concave surface (S₁) of said first lens (L₁); f is the focal length of the system; d₈ is the distance between said fourth and fifth lenses (L₄, L₅); and f₅ is the focal length of said fifth lens (L₅).

Claim 4

A scanning system for scanning an optical beam (B) on a recording surface (30), said scanning system comprising: a light source (21) for generating an optical beam (B) and a deflector (28) for deflecting the optical beam (B) outgoing from said light source (21) and characterised in that the scanning system further comprises: a telecentric f-ϑ lens system (29) for imaging the optical beam (B) deflected by said deflector (28) on said recording surface (30), said telecentric f-0 lens system (29) comprising: (a) a first lens group (FL) having an entrance pupil (EP), which includes (a-1) a first meniscus lens (L₁) having a positive power, said first lens having a concave surface (S₁) which is directed to said entrance pupil (EP), (a-2) a second lens (L₂) having a negative power, and (a-3) third and fourth meniscus lenses (L₃, L₄) having a positive power, respectively; and (b) a second lens group (RL) including a fifth lens (L₅) having a positive power, said first through fifth lenses (L₁, L₅) being successfully disposed in order from said entrance pupil (EP) side.

Claim 5

A scanning system for scanning an optical beam (B) on a recording surface (30), said scanning system comprising: a light source (21) for generating an optical beam (B) and a deflector (28) for deflecting the optical beam (B) outgoing from said light source (21) and characterised in that the scanning system further comprises: a telecentric f-ϑ lens system (29) for imaging the optical beam (B) deflected by said deflector (28) on said recording surface (30), said telecentric f-0 lens system (29) comprising: (a) a first lens group (FL) having an entrance pupil (EP), which includes (a-1) a first meniscus lens (L₁) having a positive power, said first lens having a concave surface (S₁) which is directed to said entrance pupil (EP), (a-2) a second lens (L₂) having a negative power, and (a-3) third and fourth meniscus lenses (L₃, L₄) having a positive power, respectively; and (b) a second lens group (RL) including a fifth lens (L₅) having a positive power, said first through fifth lenses (L₁, L₅) being successfully disposed in order from said entrance pupil (EP) side.

Claim 6

A scanning system according to Claim 3, wherein said telecentric f-ϑ lens system satisfies the following: -0.65<(r₁/f)<-0.25 0.4 < (d₈/f) < 1.16 1.61 < (f₅/f) < 3.5 where r₁ is the radius of curvature of said concave surface (S₁) of said first lens (L₁); f is the focal length of the system; d₈ is the distance between said fourth and fifth lenses (L₄, L₅); and f₅ is the focal length of said fifth lens (L₅).