| 摘要 |
A variable focal length lens system and an image pickup device are provided to keep high magnification ratio and high performance by reducing the magnification rate assigned to a second lens group and simplifying a third lens group. A variable focal length lens system(1) comprises a first lens group(G1) having positive refractive force, a second lens group(G2) having negative refractive force, a third lens group(G3) having positive refractive force, a fourth lens group(G4) having positive refractive force, and a fifth lens group(G5), which are aligned from an object in order. If the position of a lens is changed from a wide angle view stage to a telescopic angle view stage, the first, second, third, and fourth lens groups move. The second lens group moves toward an image side and the third lens group moves toward the object to increase a gap between the first and second lens groups and decrease a gap between the second and third lens groups. The fourth lens group moves in a direction of an optical axis to compensate the position change of an image surface(IMG) accompanied with the movement of each lens group. The fifth lens group comprises a negative partial group(L51) having the negative refractive force and a positive partial group(L52) having the positive refractive force. The variable focal length lens system satisfies the following formula, 0.5<(beta2t/beta2w)/Z<0.85. The beta2t is transverse magnification of the second lens group in the telescopic angle view stage. The beta2w is transverse magnification of the second lens group in the wide angle view stage. The Z is a zoom ratio.
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