| 摘要 |
PURPOSE:To vary the focal distance in a simple and high-speed way and with a compact constitution, by giving a distribution to the optical thickness in a prescribed axial direction, setting at least two optical eoements opposite to each other and turning at least one optical element around a shaft. CONSTITUTION:The thicknesses t1 and t2 of optical elements 1 and 2 are set so as to satisfy t1=Athetar<2>+B1r<2>+C1 and t2=-Athetar<2>+B2r<2>+C2 in a plane coordinate display, where A, B1, B2, C1 and C2 are constants respectively. Such elements 1 and 2 are set opposite to each other, and the element 1 is turned in the direction of theta around a shaft of r=0 by an extent DELTAtheta. For instance, B1= B2=C2=0 is satisfied and the refractive index is set at (n) for the elements 1 and 2. Under such conditions, the focal distance (f) of this optical system is defined as f=1/2A(n-1)DELTAtheta and furthermore the distance (f) can be set to the plus or minus value in accordance with the turning direction of the element 1. In such way, the focal distance can be varied in a simple and quick way with a compact constitution. |
