| 摘要 |
An optical instrument comprises a housing and at least one optical assembly enclosed by said housing and mounted on a stage plate 5. The stage plate is supported on the base plate 1 with the aid of supporting means 2, 3, 4 which guarantees on the one hand a precise fixing of the stage plate compared to the base plate and thus the housing, and on the other hand allows the base plate to distort eg under high temperatures without a transfer to the stage plate. There are three supporting structures of different kinds which fix three different points by ball-and-socket type joints. Upon the disconnection of the third supporting structure 4 the stage plate can be lifted like a lid around an axis which is the middle axis of the first and a second supporting structures 2, 3. The optical assembly uses a split laser beam to effect Doppler shift measurement of a moving liquid surface or solid body eg 10 measure length and/or velocity of a rail produced by rolling. <IMAGE>
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