A telephoto lens includes, in order from the object side, a first lens unit having
a positive refracting power, a second lens unit having a negative refracting power,
a third lens unit having a positive refracting power, and a fourth lens unit having
a negative refracting power. The second lens unit has a cemented lens composed
of a positive lens and a negative lens, and a negative lens. The fourth lens unit
has a cemented lens composed of a negative lens and a positive lens, and a negative
lens. The telephoto lens satisfies the following conditions:
where d is an Abbe's number of a lens having a positive refracting
power in the first lens unit, f4 is a focal length of the fourth lens
unit, and f is a focal length of the entire optical system.
