| 摘要 |
PURPOSE:To improve the stability of an optical system and the reproducibility of an image and to attain easy adjustment by arranging a semitransparent screen for projecting light transmitted through the holes of an object to be measured to a focus position on the approximately front side of a lens between a lens and the object to be measured. CONSTITUTION:When the holes 20a of a printed substrate 20 are passed on a gap 7, light beams are transmitted through the holes 20a and projected on the screen 17 and bright circles 17a having the same diameter as the holes 20a are formed on the positions of the holes 20a. The light beams are converged by plural lens elements 16a in a lens 16 and projected to the photodetecting face 15a of a CCD optical sensor 15. Since the screen 17 is arranged on the focus surface on the front side of the lens 16, the light beams forming the circles 17a are converged on the focus face on the rear side of the lens 16 by the lens 16. Consequently, the shape of each circle 17a can be faithfully reproduced on the photodetecting surface 15a. Although the clearness of the circles 17a is influenced by an interval between the substrate 20 and the screen 17, the interval is narrow and the light beams L are parallel beams, the light beams transmitted through the holes 20a are projected straight, so that the size of the interval can be neglected. Thereby, a defocusing observed from the photosensitive face 15a can be removed and the reproducibility of the images of the holes 20a can be prevented from being dropped.
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