| 摘要 |
<p>A zoom lens includes a first lens unit having a positive refracting power and is fixed during zooming, second lens unit having a negative refracting power and is movable during zooming, third lens unit having a positive refracting power and used to correct image surface by the zooming, and fourth lens unit having a positive refracting power. These lens units are arranged in the order named from the object side. In order to properly correct halo/coma that tends to occur during zooming, an aspherical surface is formed in the third lens unit at a focal length fm given by fm = fw·z 1/2 , where fw is the wide-angle focal length, and z is the zoom ratio, when the imaging magnifications of the second and third lens units simultaneously pass through a -1-time point during zooming.</p> |
