Telephoto lens system

A telephoto lens system comprising, in order from an object to an image side:

• a first lens unit of positive refracting power;
• a second lens unit of positive refracting power;
• a third lens unit of negative refracting power;
• and
• a fourth lens unit of positive refracting power,
• said first lens unit comprising, in order from said object side, two positive lenses and a negative meniscus lens having a concave surface with a strong curvature on said image surface side,
• said second lens unit comprising a positive lens having a convex surface with a strong curvature on said object side and a doublet consisting of negative and positive lenses,
• said third lens unit comprising a doublet consisting of negative and positive lenses, and
• said fourth lens unit comprising a cemented doublet consisting of negative and positive lenses,
• wherein said third and fourth lens units are movably attached for focusing, and
• said first and second lens units remain fixed and further conform to the following four conditions (1) to (4):
• 0. 3<f.sub.1 /f.sub.2 <1.5 (1)
• 0.1<D.sub.1 /f.sub.12 <0.55 (2)
• 0.15<-f.sub.3 /f.sub.4 <1.0 (3)
• 0.3<-.DELTA.X.sub.3 /.DELTA.X.sub.4 <3.1 (4)
• where:
• f.sub.1 is the focal length of the first lens unit,
• f.sub.2 is the focal length of the second lens unit,
• f.sub.3 is the focal length of the third lens unit,
• f.sub.4 is the focal length of the fourth lens unit,
• f.sub.12 is the composite focal length of the first and second lens units on the object point at infinity,
• .DELTA.X.sub.3 is the amount of focusing movement of the third lens unit from the object point at infinity to the shortest object distance with the proviso that a plus sign indicates the movement of the third lens unit from the reference position on the object point at infinity to the image surface side,
• .DELTA.X.sub.4 is the amount of focusing movement of the fourth lens unit from the object point at infinity to the shortest object distance with the proviso that a plus sign indicates the movement of the fourth lens unit from the reference position on the object point at infinity to the image surface side, and
• D.sub.1 is the real separation between the first and second lens units.