| 摘要 |
PURPOSE:To reduce distortion aberrations while achieving compactification and wider angle by combining plural pieces of concave and convex lenses. CONSTITUTION:From the object face side, the 1st group L1 which is composed of a concave lens l1 and has a negative focal length and the 2nd group L2 which consists of convex lenses l2, l3 and has a positive focal length are so arrayed that formulas 1 thru 3 are satisfied where f is let to be the compound focal length of the total system, f1 is let to be the focal length of the 1st group L1, f2 to be the focal length of the 2nd group L2 and na, nb are the refractive indices of the convex lenses l2, l3. This enables compactification and wider angle to be achieved and distortion aberrations to be sufficiently corrected with less number of constituting lenses and enables the optical system which is capable of approaching the spot diameter of the beam to the diffraction limit on the image plane to be obtained. |
