| 摘要 |
PURPOSE:To obtain a desired soft gradation image after focusing by making the mutual disposition of lens groups changeable from the state that aberrations are sharply corrected to the state that the amount of generation of spherical aberrations is large, without entailing substantial fluctuations in paraxial image plane position. CONSTITUTION:A lens system is divided to group A and group B by a variable air space dBO. This air space dBO is sandwiched by the two faces directing their concave faces to the position where the full aperture main beam intersects with the optical axis. The amount of generation of spherical aberrations is changed by expanding or contracting such variable air space. More specifically, if the space dBO is expanded by parting the group A and the group B, the spherical aberrations are insufficiently corrected. Conversely, if the space dBO is decreased, the correction is excess. If the spherical aberrations are at a minimum 20rhof (rho is a permissible inside diameter of confusion), this lens is usable as a soft focus lens. |
