| 摘要 |
PURPOSE:To correct the coma aberration which is generated when astigmatism is corrected sufficiently, by giving a refractive index distribution to a lens element in the optical-axial direction. CONSTITUTION:When the distribution refractive index of the second positive meniscus lens is reduced monotonously from the object side to the image side, the power of the third face for the light which passes through the peripheral part of this second positive lens is weakened, and thus, this method is effective for correction of the coma aberration. If a variation DELTAN of refractive indexes of the second positive lens and the third negative lens is smaller than 0.0004f (f is the focal length (mm.) of the whole of the system), it is difficult that this method has not a sufficient effect though there is an advantage in the working and if the variation DELTAN is larger than 0.06, it is difficult that lenses are produced easily with a current producing technique.
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