| 摘要 |
PURPOSE:To stably attain accurate measurement of a beam spot by splitting a light beam passing through an observing objective lens into a 1st and 2nd split light beams, leading the 1st split light beam to an observing section and leading the 2nd split light beam to an image pickup means so as to apply focus control of the objective lens based on an image pickup output signal from the image pickup means. CONSTITUTION:The 1st split light beam is led to the observing section 51 and the 2nd split light beam is led to the image pickup means of a focus state detection section 52 and the image pickup means picks up a beam spot formed by the 2nd split light beam and a detection output signal in response to the focus state informing the beam spot of the 1st split beam in the observing section is formed based on the image pickup output signal obtained therefrom. Thus, the beam spot is observed accurately and stably. |
