| CPC G02B 9/60 (2013.01) | 7 Claims |
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1. An imaging lens comprising, in order from an object side to an image side,
a first lens with positive refractive power,
a second lens with negative refractive power,
a third lens,
a fourth lens with positive refractive power, and
a fifth lens with negative refractive power,
wherein said first lens has an object-side surface being convex in a paraxial region, said third lens has an image-side surface being convex in a paraxial region, and said fifth lens is formed in a biconcave shape having an object-side surface being concave and an image-side surface being concave in a paraxial region, and the following conditional expressions (1), (2), (3), (4) and (21a) are satisfied:
−9.00<r3/r7/D2<−4.20 (1)
0.10<r5/r6 (2)
r7/T2<−9.00 (3)
0.50<r10/(D5−T4)<9.50 (4)
0.20<(f4/f)+(f5/f)<0.45 (21a)
where
r3: a paraxial curvature radius of an object-side surface of the second lens,
r7: a paraxial curvature radius of an object-side surface of the fourth lens,
D2: a thickness along the optical axis of the second lens,
r5: a paraxial curvature radius of an object-side surface of the third lens,
r6: a paraxial curvature radius of an image-side surface of the third lens,
T2: a distance along the optical axis from an image-side surface of the second lens to an object-side surface of the third lens,
r10: a paraxial curvature radius of an image-side surface of the fifth lens,
D5: a thickness along the optical axis of the fifth lens,
T4: a distance along the optical axis from an image-side surface of the fourth lens to an object-side surface of the fifth lens,
f4: a focal length of the fourth lens,
f5: a focal length of the fifth lens, and
f: a focal length of the overall optical system of the imaging lens.
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