| 摘要 |
PURPOSE:To always observe a distinct image even when a position of a pupil is varied by utilizing a dispersing action of a transparent refractive optical element, giving an incident angle difference and an optical path length difference to a diffraction grating optical element with respect to light beams of each wavelength of a luminous flux having prescribed wavelength width and suppressing a chromatic aberration generated by the diffraction grating optical element. CONSTITUTION:An axial chromatic aberration caused by a color dispersion generated by a diffraction grating optical element 10 is negated by an effect of a color dispersion tending in the reverse direction generated by a triangular prism 41. Also, there is a misalignment in the optical axis direction of aberration formed by a light beam 20 of wavelength lambdaB generated by the diffraction grating optical element 10. It is correct by a misalignment of a virtual image formed position in the tendency reverse to the diffraction grating optical element 10, caused by a refractive index difference and an optical path length difference between the light beam 20 of wavelength lambdaA and the light beam 21 of wavelength lambdaB generated in the triangular prism 41. In such a way, the axial chromatic aberration generated by the diffraction grating optical element 10 is corrected roughly satisfactorily. Therefore, even when a pupil position has moved in the direction being orthogonal to the optical axis, a distinct image can be observed. |
