1. Field of the Invention
The present invention relates to an optical lens assembly for image pickup, and more particularly to the optical lens assembly for image pickup to provide a good image quality to satisfy the specifications for electronic products.
2. Description of the Related Art
Compact electronic products such as digital still cameras and mobile phone cameras are generally equipped with an optical lens assembly for image pickup for capturing images of an object, and the optical lens assembly for image pickup tends to be developed with a compact design and a low-cost while achieving a good aberration correction capability, and providing high resolution and superior image quality.
In general, a conventional optical lens assembly for image pickup of a compact electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. Although the optical lens assembly for image pickup with the four-lens or five-lens designs has advantages on image aberration and modulation transfer function (MTF) performance, it comes with a high cost. The optical lens assembly for image pickup with the two-lens design usually cannot meet the high resolution requirement. Therefore, the optical lens assembly for image pickup with the three-lens design is usually taken into consideration as a first priority for the design.
In various compact designs of the three-lens optical lens assembly for image pickup having a fixed focal length, prior arts usually adopt a design with a combination of positive refractive power or negative refractive power, particularly the design of a first lens element closest to the image side having positive refractive power to increase the optical magnification of the optical lens assembly for image pickup, and prior arts usually adopt a design with bi-convex lens or a meniscus lens with a convex object-side surface as disclosed in U.S. Pat. No. 7,710,662 and U.S. Publication US2009/046380. Although the first lens element closest to the object side has stronger positive refractive power to provide a better light condensation, yet the aberration cannot be compensated or corrected by the second lens element and the third lens element easily. As a result, the high quality requirement of the optical lens assembly for image pickup cannot be achieved. To overcome this drawback, a concave object-side surface of the first lens element is adopted in the design as disclosed in U.S. Pat. No. 7,301,712, such that the positive refractive power of the first lens element will not be excessive, and a concave object-side surface of the second lens element is adopted in the design to achieve the effect of reducing the total length of the optical lens assembly for image pickup. However, the curvature of the second lens element encounters a large change, and thus incurring a difficult manufacture. In addition, the refractive power of the second lens element is higher than the refractive power of the first lens element; a chromatic aberration occurs at edges of the optical lens assembly for image pickup and a more serious aberration results.
To overcome the aforementioned drawbacks of the prior arts, a better design for compensating the aberration and limiting the total length of the optical lens assembly for image pickup is required for the use in compact electronic devices. Therefore, the present invention provides a more practical design and adopts a combination of different refractive powers and a combination of convex and concave optical surfaces for three lens elements to achieve the effects of improving the imaging quality, lowering the cost for mass production, and applying the design in electronic products.