Zoom lens

Abstract

A zoom lens for television broadcasting cameras suitable for both regular and high definition television (HDTV) format cameras is disclosed. The zoom lens is formed of a zoom lens main body having four lens groups and a supportive lens attachment that may be removably inserted in the optical path of the fourth lens group. In order from the object side, the first lens group is stationary when zooming and has positive refractive power, the second lens group has negative refractive power and moves to accomplish zooming, the third lens group may be of either negative or positive refractive power and shifts in position when zooming in order to maintain the image surface at a fixed position, and the fourth lens group is composed of two sub-assemblies which are fixed in position and separated from one another a distance sufficient to enable a supportive lens attachment to be inserted in the light path of the zoom lens when the zoom lens is used for imaging onto an image sensor having HDTV format. The supportive lens attachment if formed of a positive lens group and a negative lens group. When inserted with the positive lens group nearest the object side, the supportive lens attachment increases the focal length of the zoom lens, thereby forming a larger image which fully illuminates the wider format of an HDTV image sensor. When imaging for regular television, in which the aspect ratio (width to height) of the image sensor is 4:3, the supportive lens attachment 4 is withdrawn from the optical path. When imaging for HDTV, which uses image sensors having an aspect ratio of 16:9, the above-mentioned supportive lens attachment is inserted into the optical path. The supportive lens attachment is formed of positive and negative lens groups, which preferably meet a specified condition.

Dependencies are inferred from the claim text.