| 摘要 |
PURPOSE:To suppress aberrations low at any power by providing movable positive lens groups which are positioned symmetrically or nearly symmetrically about a stop and movable negative lens groups which are positioned symmetrically or almost symmetrically about the stop. CONSTITUTION:This optical system consists of the 1st lens group I which is negative on the whole, the 2nd lens group II which is negative on the whole, the 3rd lens group III which is positive on the whole, and the 4th lens group IV which is negative on the whole successively from the object side to the image side. The 1st lens group I and the 4th lens group IV are symmetrical about the stop 10 of the optical system and the 2nd lens group II and the 3rd lens group III are symmetrical so as to maintain symmetry on the whole. Therefore, aberrations are suppressed small at any power and the distance between object images is held constant, so when the power is varied from life size to, e.g. enlargement or reduction size, the respective lens groups are so moved that the gap between the 2nd group II and the 3rd group III is narrowed down and the gap between the 1st group I and the 2nd group II and the gap between the 3rd group III and the 4th group IV are increased. |
