PURPOSE: To compensate temperature variation by composing a zoom lens of the 1st group with positive refracting power, a variator and a compensator with negative refracting power, and the 4th group for image forming operation, using plastic lenses, and specifying the power relation among the 1st W the 3rd groups.
CONSTITUTION: The zoom lens consists of the 1st W the 3rd lens groups constituting a variable power system and the 4th lens group for image forming operation, the 1st and the 2nd groups have positive power and negative power respectively, and the lens groups constituting the variable power system are all composed of lenses using the same kind of plastic materials. Then when ψIWψII are the power values of the respective groups and hIWhII are the heights of light beams, it is made to satisfy 1+hII2ψII+hIII2ψIII=0 so as to compensate variation of an image forming surface due to temperature variation; and -18.8<ψII<-1, ψIII>0, and -1>ψII/ψIII>0.23ψII-6 so as to meet requirements for zooming. A shift in variable power image position is made to meet both requirements.
MARUYAMA TAKESUKE
AZUMI TAKASHI
| JPS5865407A | 1983-04-19 |
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