| 摘要 |
<p>A dual field optical system 20 comprises an objective A, B, which forms an intermediate image 10 and a relay E,F, which transfers radiation to a focal plane 12. The objective A, B comprises a primary mirror A and a secondary mirror B arranged in the form of a Cassegrain system and is rendered dual-field by the provision of an alternative primary mirror A<1> which is axially movable between in-use and out-of-use positions. The primary mirror A forms part of a housing J for a linear actuator 15 which is connected by co-axial rods 14 to the alternative primary mirror A<1> so that the system is both compact and of low mass due to symmetry. <IMAGE></p> |
