| 摘要 |
A ray of light incident via a pin hole (6) and a field stop (7) having a field of vision a predetermined angle larger than a telescope's actual field of vision that are disposed on an axis (5) in parallel to the optical axis (4) of the telescope is measured in intensity by a photoelectric element (8). When a quantity of light incident on the photoelectric element is larger than a predetermined quantity of light, a shutter (11) is inserted into an optical path of the telescope to cut off a ray of light going into the eyes of the observer. Since an incidence of a quantity of light in excess of a predetermined one into a field of vision a predetermined angle larger than the actual field of vision of the telescope will block the optical path of the telescope, a risk such as damage to the eyes of the observer can be eliminated to prevent an accident even when the observer erroneously observes a strong light-generating object such as the sun. <IMAGE> |
