Great relative aperture telephoto zoom lens

A great relative aperture telephoto zoom lens of four-unit construction having in succession from the object side:

• a first lens unit having positive refractive power;
• a second lens unit having negative refractive power;
• a third lens unit having positive refractive power;
• and
• a fourth lens unit having positive refractive power;
• said fourth lens unit having, in succession from the object side, a front group having positive refractive power and a rear group having positive refractive power;
• said front group having, in succession from the object side, two positive lens components and a negative lens component;
• said rear group having, in succession from the object side, a positive lens component and a negative lens component, and being designed to satisfy the following conditions:
• 1.5<f.sub.4 /(D.sub.41 .multidot.f.sub.n)<3.0
• 3.1<D.sub.41 /D.sub.42 <4.8
• -3.7<q.sub.43 <-1.2
• where
• f.sub.4 :
• the focal length of the fourth lens unit;
• Fn:
• F number of the entire system;
• D.sub.41 :
• the air gap from the image side lens surface of that positive lens component in the front group in the fourth lens unit which is most adjacent to the image side to the object side lens surface of that lens component in the rear group in the fourth lens unit which is most adjacent to the object side;
• D.sub.42 :
• the air gap from the image side lens surface of that lens component in the rear group in the fourth lens unit which is most adjacent to the object side to the object side lens surface of that lens component in the rear group in the fourth lens unit which is most adjacent to the image side;
• q.sub.43 :
• the shape factor of the negative lens component in the front group in the fourth lens unit, it being to be understood that when the radius of curvature of the object side lens surface is ra and the radius of curvature of the image side lens surface is rb, the shape factor q is defined by q=(rb+ra)/(rb-ra).