| 摘要 |
A Keplerian zoom finder optical system comprises an objective lens group having a positive refracting power on the whole and constructed of, in order from an object side, a first lens unit having a negative refracting power, a second lens unit having a positive refracting power, a third lens unit having a negative refracting power and a fourth lens unit having a positive refracting power. This finder also comprises a regulating element, disposed in the vicinity of a focal position of the objective lens group, for regulating a visual field. The finder further comprises an eyepiece unit having a positive refracting power. The finder varies a magnification by moving at least the second lens unit along an optical axis and satisfies the following condition:-5<f3/fw<-3where fw: the synthetic focal length of the first and second lens units in a minimum magnification state, and f3: the focal length of the third lens unit.
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