| 摘要 |
PROBLEM TO BE SOLVED: To eliminate a variation of MTF characteristic due to the wavelength of a trap frequency and to suppress the increasing of a pitch and to obtain a satisfactory suppression effect of pseudo color by overlapping at least two sheets of triangle wave phase type plates having different characteristics so that respective grating patterns become parallel. SOLUTION: In a triangle wave type phase plate, when a trap frequency is 70 (1/mm) and a reference frequency is 550nm, a characteristic like (a) is obtained. In a triangle wave type phase plate in which a pitch is made to be 1.3∼1.5 times the pitch of the triangle wave type phase plate having the characteristic of (a) and the height of ruggedness is made to be 0.4∼0.6 times the height of the ruggedness of the phase plate, a characteristic like (b) is obtained. When the triangle wave type phase plate having the characteristic of (a) and the triangle wave type phase plate having the characteristic of (b) are combined and the are formed so that respective grating patterns become parallel each other on the surface and the rear of the phase plates, a characteristic of the plates become an MTF characteristic like (c). When the MIF is <=0.1, a characteristic having no practical problem is obtained because of suppression of psudo color.
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