Variable magnification lens system

A variable magnification lens system, essentially consisting of from the object side:

• a positive first lens unit including a negative first lens element and a positive second lens element, and
• a negative second lens unit including a positive third lens element and a negative fourth lens element;
• wherein, at variable magnification from an equal magnification state to an enlargement state, the overall lens system moves while the spacing between said two lens units is increased, and the distance between the object and the image remains constant;
• an aspherical surface is provided on at least one surface of the first lens unit and at least one surface of the second lens unit;
• a concave surface is provided on the object side surface of the first lens element and on the image side surface of the fourth lens element;
• and
• a following condition is fulfilled:
• 1.5<.vertline.(f.sub.I *f.sub.1)/(f.sub.II *f.sub.4).vertline.<2.5
• where the following definitions obtain:
• f.sub.I :
• first lens unit focal length
• f.sub.1 :
• first lens element focal length
• f.sub.II :
• second lens unit focal length
• f.sub.4 :
• fourth lens element focal length.

A variable magnification lens system, consisting of from the object side:

• a positive first lens unit including a negative first lens element, a positive second lens element, and a diaphragm, and
• a negative second lens unit including a positive third lens element and a negative fourth lens element;
• wherein, at variable magnification from an equal magnification state to an enlargement state, the overall lens system moves while the spacing between said two lens units is increased, and the distance between the object and the image remains constant;
• an aspherical surface is provided on at least one surface of the first lens unit and at least one surface of the second lens unit;
• a concave surface is provided on the object side surface of the first lens element and on the image side surface of the fourth lens element;
• and
• a following condition is fulfilled:
• 1. 5<.vertline.(f.sub.I *f.sub.1)/(f.sub.II *f.sub.4).vertline.<2.5
• where the following definitions obtain:
• f.sub.I :
• first lens unit focal length
• f.sub.1 :
• first lens element focal length
• f.sub.II :
• second lens unit focal length
• f.sub.4 :
• fourth lens element focal length.