Zoom lens with three lens elements

摘要

The zoom lens has a first positive lens group (I) which is followed by a second lens group (II) which is also positive. The third and final lens group (III) is negative. The individual lens elements in each of the three lens groups remain fixed with respect to each other and the gaps (d6,d15) between the first and second and the second and third lens groups are changed as the focal length of the lens is altered. The gaps may be altered in accordance with given formulae as the lens is moved from its wide angle to its telescopic setting. As the focal length is increased, the whole lens moves away from the focal plane, while the first inter-group gap (d6) is increased and the second (d15) is decreased.