| 摘要 |
This invention provides an imaging optical lens system comprising three lens elements with refractive power: a positive first lens element having a convex object-side surface at a paraxial region; a negative plastic second lens element having a convex or flat object-side surface and a concave image-side surface at a paraxial region, and both the object-side surface and the image-side surface being aspheric; and a negative plastic third lens element having a concave object-side surface at a paraxial region, the shape of the image-side surface thereof changing from concave when near an optical axis to convex when away from the optical axis, and both the object-side surface and the image-side surface being aspheric. The aforesaid arrangement can not only effectively correct the astigmatism of the system against defocus problems but also effectively reduce the back focal length for desirable space usage. Therefore, the lens system can be more compact.
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