1. Technical Field
The present invention relates to an optical image system. More particularly, the present invention relates to a compact optical image system applicable to electronic products.
2. Description of Related Art
In recent years, with the popularity of mobile products with camera functionalities, the demand for miniaturizing an optical lens system is increasing. The sensor of a conventional photographing camera is typically a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor. As advanced semiconductor manufacturing technologies have allowed the pixel size of sensors to be reduced and compact optical lens systems have gradually evolved toward the field of higher megapixels, there is an increasing demand for compact optical lens systems featuring better image quality.
A conventional compact optical lens system employed in a portable electronic product mainly adopts a four-element lens structure, such as U.S. Pat. No. 7,969,664. Due to the popularity of mobile products with high-end specifications, such as smart phones and PDAs (Personal Digital Assistants), the pixel and image-quality requirements of the compact optical lens system have increased rapidly. However, the conventional four-element lens structure cannot satisfy the requirements of the compact optical lens system.
Another conventional compact optical lens system has five-element lens structure, such as U.S. Pat. No. 8,000,031. The optical lens system has a flat element located on the back focal location for filtering infrared rays or securing an image sensor. However, the total track length would be hardly reduced by the thickness of the flat element, and the essential distance between the flat element and other lens elements for avoiding interference.