| 摘要 |
PURPOSE:To focus the image of even an object having no contrast by arranging a visible rays-transmissive plate, where a prescribed pattern for invisible rays is formed, near the position of a field stop in an illumination optical system and detecting the focus with a signal corresponding to the image of the invisible- rays pattern. CONSTITUTION:An infrared pattern filter P is arranged in the position of a field stop 3 which is conjugate to an object and an image surface 13 with respect to an object lens 6. The light transmitted through the infrared pattern filter P passes through a condenser lens 4, the first half mirror 5, and the object lens 6 and is reflected on an object 7 and reaches the image surface 13 through the object lens 6 and half mirrors 5 and 8. Meanwhile, the luminous flux reflected on the half mirror 8 becomes only infrared-ray components by a half mirror infrared filter 9 and is divided to two luminous fluxes 11a and 11b by an optical path dividing prism 10, and they are made incident to an image sensor 12 to detect and compare the contrast of the image of the object. Then, a stage driving motor 15 is operated on a basis of a signal from a focus detecting circuit 14, and a stage 16 is moved in the direction of the optical axis to focus the image of the object automatically. |
