| 摘要 |
PURPOSE:To facilitate adjustment control and to improve resolution by arranging only one scale having an index grating on the surface and a concave mirror opposite to each other in a relatively movable state. CONSTITUTION:An optical grating 15a which is the index grating is formed on the surface of the movable scale 15. The concave mirror 16 is arranged over the movable scale 15 opposite at a proper interval. Image pickup light is projected on one index grating image pickup point 19 on the scale 15 from a projection part 17. The image pickup light is reflected by the concave mirror 16 to form an image on the scale 15, and a photodetection part 18 which detects the formed image is provided facing a moire fringe composition point 20. |
