JPS6442617A - Lens system with variable focal distance - Google Patents

Abstract

PURPOSE:To easily obtain a high variable power ratio, and also, to reduce the aberration fluctuation before and after the variable power, by providing plural auxiliary lens systems having negative refracting power on the optical axis in the rear of a main lens system, and inserting and attaching successively these auxiliary lens systems. CONSTITUTION:A first auxiliary lens system 2 having negative refracting power and a second auxiliary lens system 3 having negative refracting power are placed successively so as to be insertable and detachable on the optical axis of a main lens system 1, in the rear of the main lens system 1 having positive refracting power. In such a state, a third photographing system is constituted by transferring out the main lens system 1 and the first auxiliary system 1 and the first auxiliary lens system 2 to an object side, and also, inserting the second auxiliary lens system 3 onto the optical axis in the rear of the first auxiliary lens system 2, and for instance, the third photographing of a long focal distance is executed. That is, it is constituted so that photographing of a long focal distance can be easily executed by forming the whole lens system as a telescope type. Also, even in case of any photographing, focusing is executed by moving only the main lens system 1, so that the transfer-out quantity to the same object distance is made constant. In such a way, while maintaining a satisfactory optical performance, photographing of three or more focal distances can be easily executed.