| 摘要 |
PURPOSE:To maintain always efficient image formation performance by moving the post group out of the 4th lens group at a format different from that in case of absence of an extender when the extender is arranged between the pre-group and post group of the 4th lens group. CONSTITUTION:Ordinarily, a part of the 4th lens group G4 to be a relay group fixed on an image plane is moved along its optical axis at the time of power variation. Namely, a part of an aberration variation correcting work is shared to the moved lens group to reduce the aberration correcting load of a variable power part and to suppress the variation of aberration due to zooming at an extremely low level. The aberration variation correcting function based upon the movement of a part of the relay group is effectively appplied also to the correction of aberration variation under the extender loaded status. The correcting work of aberration variation can be shared to the power variable part consisting of the 1st-3rd lens groups G1-G3 and the relay group (4th lens group G4) for image formation and the pre-group G1 of the 1st-4th lens group G1-G4 forms an almost afocal system as a whole, so that both the variation of spherical aberration and image surface curve can be corrected. |
