Zoom lens system for use in a copying apparatus

A zoom lens system for use in a copying apparatus, comprising from the object side:

• a first lens unit including a first lens element which is a positive meniscus lens element convex to the object side;
• a second lens unit including a second lens element which is a bi-concave lens element whose object side surface has a larger radius of curvature;
• a third lens unit including a third lens element which is a bi-convex lens element;
• and
• a fourth lens unit including a fourth lens element which is a negative meniscus lens element concave to the image side,
• wherein zooming is performed by moving the entire lens system along the optical axis while varying, during zooming to a magnification larger than unity, at least a distance between the second and third lens elements and a distance between the third and fourth lens elements so as to be larger than the distances therebetween obtained at unity magnification and varying, during zooming to a magnification smaller than unity, distances between all the lens elements so as to be larger than the distances therebetween obtained at unity magnification,
• and wherein during zooming, the following conditions are fulfilled:
• .DELTA.d2<.DELTA.d4<.DELTA.d6
• where .DELTA.d2 represents a variation amount of a distance between the first and second lens elements from the distance therebetween obtained at unity magnification, .DELTA.d4 represents a variation amount of the distance between the second and third lens elements from the distance therebetween obtained at unity magnification, and .DELTA.d6 represents a variation amount of the distance between the third and fourth lens elements from the distance therebetween obtained at unity magnification.

A zoom lens system for use in a copying apparatus, comprising from the object side:

• a first lens unit including a first lens element which is a positive meniscus lens element convex to the object side;
• a second lens unit including a second lens element which is a bi-concave lens element whose object side surface has a larger radius of curvature and a third lens element which is a bi-convex lens element;
• and
• a third lens unit including a fourth lens element which is a negative meniscus lens element concave to the image side,
• wherein zooming is performed while a conjugate distance is kept constant by moving the entire lens system along the optical axis while varying a distance between the first and second lens units and a distance between the second and third lens units,
• and wherein the following conditions are fulfilled:
• ##EQU11## where d2 represents a distance between the first and second lens units at unity magnification, d2' represents a distance between the second and third lens unit at magnifications other than unity, .DELTA.d2 represents a variation amount of the distance between the first and second lens units during zooming and .DELTA.d6 represents a variation amount of the distance between the second and third lens units during zooming.