| 摘要 |
PURPOSE:To obtain the bright, small-sized wide-angle lens whose F number and telephoto ratio are both small by providing the 1st positive meniscus lens having the convex surface on an object side, the 2nd lens, the 3rd negative lens, the 4th positive lens, and the 5th negative meniscus lens which has the concave surface on the object side, and controlling their refractive indexes and focal lengths on specific conditions. CONSTITUTION:Specific conditions are shown by inequalities 1-8. Deterioration in spherical aberration and coma originating from a decrease in Petzval's sum by decreasing the refractive indexes of the 1st and the 2nd lenses and increasing the refractive index of the 3rd lens is compensated by making both surfaces of the 4th lens aspherical. Namely, the 4th lens is provided with a flection point on the periphery of the radial intermediate part, the center part inside the periphery is made convex and the outside peripheral part is made concave. Then, a flection point is provided on the periphery of the radial intermediate part in the front aspherical surface of the 4th lens for correcting the overcompensation of spherical aberration. The 5th lens does not have distortion and coma aberration at an intermediate field angle compensated completely when spherical surface constitution is employed, so both surfaces are made aspherical.
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