| 摘要 |
PROBLEM TO BE SOLVED: To make an optical system small in size and light in weight, and also, to reduce the cost of the system as compared with both a conventional optical system for correcting the thermal aberration and an optical system for simultaneously correcting the thermal aberration and the chromatic aberration. SOLUTION: In the conventional practice, the two-lens refractive optical system is provided with lenses 1 and 2 constituted of two kinds of material, but, the optical system is constituted of one-lens optical system composed of one kind of material including a diffraction optical system which is obtained by adding a diffraction optical element 4 to one surface of a refractive lens 3. The diffraction optical element 4 is provided with a zonal belt 5 which is formed like a step on the lens surface and also which is co-axial rotation- symmetrical to the optical system. And, provided that the thermal Abbe's number of the diffraction optical element 4 is expressed by VTd and the linear expansion coefficient of materials of the element 4 is expressed byα, VTd=-1/(2α) is defined, then, the thermal aberration is corrected.
|
