FTHETA LENS

• Main Authors: UENO KAZUO, MOCHIDA YOSHIO
• Format: Patent
• Language: English
• Published: 10.03.1998
• Edition: 6
• Subjects: OPTICAL ELEMENTS, SYSTEMS, OR APPARATUS; OPTICS; PHYSICS

PROBLEM TO BE SOLVED: To obtain fθ lens which is composed of three elements, has a good telecentric characteristic, is well corrected of aberrations and has a good fθ characteristic by forming the fθ lens composed of the three elements in three groups so as to satisfy specific conditions. SOLUTION: This fθ lens is composed of the lens group composed of the three elements in three groups consisting, successively from an object side toward an image plane side, a first lens 1 of a negative meniscus lens of which the concave face is directed to the object side, a second lens 2 of a positive meniscus lens of which the concave face is directed toward the object side and a third lens 3 of a positive meniscus lens of which the convex face is directed toward the object side. The lens is so formed as to satisfy the conditions -0.9<f1 /f<-0.4, d2 /f<0.06, N1 , N2 , N3 >2, -1.2<r1 /d0 <-0.8 by defining the focal length of the entire system as f, the refractive indices of the first lens 1 to the third lens 3 as N1 to N3 , the distance from the deflection plane of a deflector to the first lens 1 as d0 , the air spacing between the first and second lenses 1, 2 as d2 and the radius of curvature of the incident surface of the first lens 1 as r1 .