| 摘要 |
PROBLEM TO BE SOLVED: To eliminate both of defocus caused by the change of optical path length and defocus caused by the change of a wavelength region and the axial chromatic aberration of an optical system by properly setting a filter. SOLUTION: In an ordinary photographing state where an infrared cut filter 2 is positioned in a converging optical path behind an image pickup optical system 1 (image side), an image surface I to the 1st wavelength region being visible light is the light receiving surface of a photoreceptor such as a CCD. Both sides of the filter 2 are formed to gently project so as to have weak positive power. In a state where the filter 2 is retreated to the outside of the optical path, for example, in an infrared photographing state such as a noctovision mode, the image surface to the 1st wavelength region is nearer to a subject side than the image surface I by as much as the change of the optical path length because the filer 2 is retreated. Namely, a front focus state is attained to the 1st wavelength region. The position of the image surface to a 2nd wavelength area being infrared wavelength in such a state is aligned with the initial image surface I.
|
