| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical device that effectively adopts an auxiliary lens used in common for image pickup lenses by extending applications for a wide converter lens or a ratio converter lens depending on the aperture of an image pickup lens and that is excellent in the weight-reduction and compactness when the auxiliary lens is used for the ratio converter lens. SOLUTION: The auxiliary lens 10 containing lenses 12, 14 in a mount 16 has an afocal magnification of 0.8 and when the auxiliary lens 10 is mounted in front of an image pickup lens 20 with a small aperture, the auxiliary lens 10 acts like a wide converter lens. On the other hand, when the auxiliary lens 10 is mounted in front of an image pickup lens with a large aperture, the auxiliary lens 10 acts like a ratio converter lens in a camera compatible with a switchable camera where the aspect ratio of an image pickup area can be switched from 16:9 into 4:3.
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