| 摘要 |
PROBLEM TO BE SOLVED: To obtain a stable observation image without generating fluctuation of brightness even if rotating the image, by not changing the polarization characteristics of light going out from an image rotating optical means regardless of the rotation of the image rotating optical means. SOLUTION: Simultaneously with theθ-rotation of an image rotating prism 162, a secondλ/4 plate 161, the prism 162 and a thirdλ/4 plate 163 areθ/rotated in relation to a fixed firstλ/4 plate 15, so that linear polarized lightθ-rotated by the plate 161 always coincides with the p-direction of total reflection of the prism 162. Accordingly, the polarization characteristic of incident light to the prism 162 is only a p-direction component regardless of the rotating quantity of the prism 162. Linear polarized light going out from the prism 162 is alsoθ-rotated in the same way as the rotation of the prism 162, but since the plate 163 is alsoθ-rotated at the same time, the linear polarized light is converted into circularly polarized light by the plate 163 so as to always become circularly polarized light regardless of the rotation of the prism 162. Polarized light going out from the image rotating mechanism 16 does not therefore have a characteristic of being rotated in relation to an optical axis like an elliptically polarized light, so that light always with a constant polarization characteristic goes out.
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