| 摘要 |
PURPOSE:To reduce the number of pieces for constituting a titled lens system although it is compact, and also to obtain a high performance by constituting said lens system with four lens groups having positive and negative refractive powers, so that the first and the fourth lens groups are moved to an object side from an image side for the purpose of zooming. CONSTITUTION:A titled lens system consists of lens groups I -IV whose refractive powers are positive, negative, positive and negative in order from an object side. Also, for the purpose of zooming to the longest focal distance state L from the shortest focal distance state S, the lens groups I, IV are moved to the object side from an image side so that an interval to the lens groups II, III is increased or decreased, respectively, and also a prescribed condition is satisfied. Accordingly, in the state S, this lens system becomes a telephoto type consisting of the lens group of positive and negative refractive powers, therefore, its overall length is very short and it becomes compact. Also, at the time of zooming from the state S to L, the lens group IV is moved by increasing its magnification, therefore, the zooming action is shared with the lens groups II, III and IV, the moving extent of zooming is reduced even if the power of each lens group is weakened, and the number of pieces for the constitution can also be decreased. |
