1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, and, in particular, to a zoom lens that is suitable for a still camera, a video camera, a digital still camera, a monitoring camera, and the like.
2. Description of the Related Art
It is required that a zoom lens used as an image pickup optical system of an image pickup apparatus including a solid-state image pickup device have a small F-number, a wide view angle, a high optical performance, and a small size as its entirety. It is also required that a drive unit for moving a lens unit during zooming operate on reduced power, image shake during zooming be suppressed, and a first lens unit disposed nearest to the object side be fixed in place during zooming so that the strength of the lens barrel can be increased.
There is a know type of zoom lens, which is called a positive lead type, in which a lens unit having a positive refractive power is disposed nearest to the object side. A positive lead type zoom lens includes, from the object side to the image side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, a fourth lens unit having a negative refractive power, and a fifth lens unit having a positive refractive power.
US2011/0194015 and Japanese Unexamined Patent Application Publication No. 2000-180722 each disclose a zoom lens in which, during zooming, a first lens unit does not move while a plurality of other lens units move, and, during focusing, lens units other than the first lens units move.
US2011/0194015 discloses a zoom lens having an angle of view for shooting at the wide angle end of about 80 degrees, a zoom ratio of about 5 times, and an F-number at the wide angle end of about 3.6.
Japanese Unexamined Patent Application Publication No. 2000-180722 discloses a zoom lens having an angle of view for shooting at the wide angle end of about 63 degrees, a zoom ratio in the range of about 25 to 30, and an F-number at the wide angle end of about 1.45.
In order to increase the view angle of a positive lead type zoom lens, which includes a first lens unit that does not move during zooming, while maintaining a predetermined F-number and a good optical performance, it is necessary that the effective aperture of the first lens be considerably large and the size of the lens barrel be increased. If the refractive powers of lens units are increased to increase the view angle while maintaining a small size of the entire zoom lens, various aberrations occur by large amounts and it becomes difficult to appropriately correct such aberrations.
The present invention provides a zoom lens having a wide view angle, a high zoom ratio, and a high aperture ratio, and a small size as its entirety; and an image pickup apparatus including the zoom lens.