| 摘要 |
PURPOSE:To prevent any change in the positional relation among prisms under the influence of heat by supporting the contact plane of each prism constituting a prism group in abutting on plural protruding parts provided adjustablly in height on a prism base plate. CONSTITUTION:The prisms 3-5 are disposed in using the light-passing plane as reference, and adhered to the prism base plate 2 with an adhesive 11 made of such as resin adhesive, etc. To the prism base plate 2, plural pieces of screws 22 are provided for each prism 3-5 as above-said height-adjustable protruding parts; the juncture planes 10 between the prisms 3-5 are abutted on the screws 22 at their extremes; the juncture planes 10 are thus supported by the screws 22 that are uniformly disposed in a manner that the screws 22 are at the apexes of a triangle, on lines extended from which are the apexes of the juncture planes 10 of the prisms 3-5. Accordingly, in case a thermal change occurs in the titled system, the juncture planes 10 are supported by the screws 22 at uniformly disposed three locations. As a result, the stresses occurring in the prisms 3-5 are made equal at the juncture planes 10, hence irregular deforming of the prisms 3-5 due to thermal expansion/contraction can be prevented.
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