| 摘要 |
PURPOSE:To allow the control of brightness and depth of field according to an object distance by providing a variable focus liquid crystal lens and a light shielding member of variable apertures and synchronizing the change of the focal length and the change of the aperture. CONSTITUTION:A concave lens 1, a polarizing plate 2, a liquid crystal 3, an optically rotatory element 5, a polarizing plate 6, and an image pickup element 8 are disposed to the front end of an endoscope and the light shielding member is constituted of the element 5, etc. The major axis of the liquid crystal 12 of the lens 3 and the oscillation direction of the linearly polarized light align and the cell acts as a strong concave lens in the state shown in the figure. The lens focuses at a remote object and the F-number is in the normal state. Switches SW1, SW2 turn on and are focused at the near point in case of the near point object; the light shielding member is simultaneously synchronized and the linearly polarized light passes the central part alone in the case of a near object. Then, the F-number increases and the depth of field increases. The focused image is thus obtd. |
