| 摘要 |
A band-limiting filter of the invention exhibits a trimodal filter characteristic, and includes, for example, band-limiting transmittance filter characteristic portions Rb, Gb, and Bb for wavelength regions of red, green, and blue, respectively. More specifically, the band-limiting transmittance filter characteristic portions Rb, Gb, and Bb, for example, have bandpass characteristics in which the respective center wavelengths are 630 nm (full width at half maximum lambda1=30 to 90 nm), 540 nm (full width at half maximum lambda2=20 to 60 nm), and 440 nm (full width at half maximum lambda3=50 to 80 nm). This makes it possible to obtain an image of a predetermined color tone by restraining an influence of spectral sensitivity characteristic of an image pickup device when the band-limiting filter is applied to a synchronous type endoscope for performing color image pickup to perform observation under normal illumination light.
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