Zoom lens for variable power copying apparatus

A zoom lens for a variable power copying apparatus comprising six lenses disposed in the following order from an object surface to an image surface, which include:

• a first lens composed of a negative lens with the orientation of a concave surface towards the object;
• a second lens composed of a positive lens;
• a third lens composed of a negative lens with the orientation of a concave surface towards the object;
• an aperture stop;
• a fourth lens composed of the same lens as the third lens with the orientation of a concave surface towards the image;
• a fifth lens composed of the same lens as the second lens;
• and
• a sixth lens composed of the same lens as the first lens with the orientation of a concave surface towards the image;
• wherein, at the time of forming a natural size scale image of an object, the first to sixth lenses are arranged symmetrically with respect to the aperture stop, and
• at the same time of forming a reduced or magnified size scale image of an object,
• the lens and the aperture stop are arranged in such a way that the first, third, fourth, and sixth lenses are fixed, and the second and fifth lenses are moved nonsymmetrically with respect to the aperture stop
• and that length of whole lens system is moved along an optical axis so that the image size is continuously varied maintaining both a conjugate length between the object surface and the image surface and a length of whole lens assembly system constant irrespective of the state of the scale.