| 摘要 |
PURPOSE:To prevent deterioration in aberration by moving a front group and rear group to an object side at different moving speeds at the time of focusing from a far distance to a near distance and forming the titled lens in a manner as to satisfy specific conditions. CONSTITUTION:The front group (GF) and rear group (GR) of the middle range telephoto lens consisting of the GF and GR having respectively positive refractive indices from the object side are moved to the object side at the separate moving speeds, by which the focusing from the far distance to the near distance is executed. The conditions 0.2<f/fR<0.7, 0.25<DELTAM<0.7, 0<=DELTAK<0.45, DELTAK<DELTAM are satisfied in this case. Here, DELTAM=DELTAB1/DELTAA1, DELTAK=DELTAB2/DELTAA2 (f) is the focal length of the entire system, fR is the focal length of the GR, DELTAA1, DELTAB1 are the moving quantity of the respective GF and GR at the time of the focusing in the state of photographing magnification beta=1/20, DELTAA2, DELTAB2 are the moving quantity of the respective GF, GR at the time of the focusing in the closed photographing state. The deterioration in the aberration is thereby prevented.
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