| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide an image forming optical system which is advantageous for sound insulation and protection against dust and is easy to reduce a radial direction and easy to secure optical performance and to provide an imaging apparatus using the image forming optical system.SOLUTION: The image forming optical system comprises, in order from an object side to an image surface side, a first lens group having positive refractive power, a second lens group having positive or negative refractive power, and a third lens group having positive refractive power and includes an aperture stop arranged between the object side surface of the first lens group and the object side surface of the second lens group. A lens closest to the object side in the first lens group and a lens closest to an image side in the third lens group are always fixed, the second lens group comprises one negative lens component, and the negative lens component is a single lens. Only the second lens group is moved on an optical axis, in focusing from a long distance to a close distance and the third lens group comprises a front sub-lens group having positive refractive power, arranged on the object side and a rear sub-lens group having negative refractive power, arranged on the image side, with the largest axial air space in the third lens group interposed therebetween.</p> |
