A zoom lens has a first lens unit having a positive refractive power, a
second lens unit having a negative refractive power, which is moved
during zooming, a third lens unit having a positive refractive power, and
a fourth lens unit having a positive refractive power, which is moved
during zooming, arranged in the mentioned order from the object side to
the image side. The zoom lens satisfies the following conditions:
0.15<|f2 |/ {square root over ((fw.times.ft))}<0.27 and 5.4021
f3/fw<10.00, where f2 and f3 are the focal lengths of the second and
third lens units respectively, and fw and ft are the focal lengths of the
zoom lens at the wide angle end and the telephoto end respectively.