| 摘要 |
PURPOSE:To set a proper initial state for starting an automatic focus adjusting mechanism by interposing a transparent member which is not close in refractive index to one of split light beams to air and has high regular transmissivity between a prism and a line sensor in the optical path of a light beam for distance measurement. CONSTITUTION:The transparent member 46 which is not close in refractive index to air and has high regular transmissivity; is arranged in the optical path of a slit light beam a which has longer geometric optical path length in the optical-axis direction up to an image formation position between a prism 38 and a line sensor 42. For example, the transparent member 46 is made of glass with thickness (t) and a refractive index (n) (about 1.5) and switched between the optical paths of both split light beams. Consequently, the geometric optical path length of the split light beam for which the transparent member is interposed up to the image formation position in the optical-axis direction becomes long and the transparent member is therefore positioned selectively to make the geometric optical path difference between the image formation positions of the split light beams longer at the time of high magnification than at the time of low magnification. |
