| 摘要 |
PURPOSE:To move some of lens groups merely on the optical axis and obtain soft effect efficiently during normal photography, to maintain the optical performance in the normal photography excellently, and to simplify lens barrel structure by setting lens constitution properly. CONSTITUTION:The effective system of the 2nd lens group is determined by the maximum on-axis luminous flux diameter during normal photography A when the F number is fixed. The effective diameter of the 2nd lens group, however, is determined by the maximum on-axis luminous flux system at the position B during soft focusing. For the purpose, the photography system in soft focusing is made brighter than in the normal photography to make more luminous flux incident on the entire image plane. Then, a photograph which has a soft front focus and a soft rear focus is obtained and marginal light is further increased in quantity to uniform soft gradation effect, thereby obtaining excellent soft effect over the entire image plane.
|
