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January 26, 2004
Olympus Develops New Free-Shaped Prism Type
Thin Lens Unit and Announces Plans to Enter
Cellphone Camera Module Market
Free-Shaped Prism Type Lens Unit
Free-Shaped Prism Type Lens Unit
Summary
Olympus Corporation (President: Tsuyoshi Kikukawa) is pleased to announce the development of an all-new, Free-Shaped Prism Type Lens Unit for use in camera-equipped cellular telephones. A prototype camera module with a thickness of 8.5 millimeters has been produced using the new lens unit, and has been demonstrated to support 1.3-megapixel resolutions. It is the thinnest such unit yet developed, and is notable for its potential to meet the performance demands of image sensors with a resolution in excess of two megapixels. A fully functional camera module incorporating the new lens unit and an image sensor is scheduled to be available in the fall of 2004.
Development Background
Camera-equipped cellular telephones have been adopted by a wide range of users and their popularity continues to grow. Accompanying this trend, there has been a dramatic increase in the performance capabilities of the digital camera component of such telephones. In fact, cellphones equipped with 2-megapixel-class camera modules have already appeared on the market.
As more precise digital zoom functions are introduced and demand for higher image definition grows, camera-equipped cellphones with even higher pixel counts are expected to appear. However, with the coaxial type lens units currently used in camera-equipped cellphones, the thickness of the lens unit increases in proportion to the pixel count, and it has been clear for some time that a different design approach is needed to move forward.
Characteristics of the Free-Shaped Prism Type Thin Lens Unit
The defining characteristic of the Olympus-developed free-shaped prism type thin lens unit is that it uses two horizontally positioned free-shaped prisms with complex light paths to deliver light to the receiving image sensor (Fig. 1). With conventional coaxial lens units, the lens elements are stacked on top of each other (Fig. 2), and to obtain the optical performance needed to support high-pixel-count image sensors, more elements must be added. As a result, the thickness of the lens unit must be increased. With free-shaped prism type lens units, the horizontal arrangement of the lenses has little impact on thickness, and it is possible to achieve the optical performance needed to support high pixel counts without increasing the overall thickness of the camera module.
In addition, the asymmetrical design of the reflective and refractive surfaces within the free-shaped prisms makes it possible to correct image aberration with a very small number of components. In the current prototype, two free-shaped prisms provide performance equivalent to a conventional coaxial lens that has three to five lens elements, and can achieve theoretical resolutions of 250 line-pairs per millimeter at the center, and 200 line-pairs per millimeter at the periphery.
The extremely complex internal light path of the free-shaped prisms also effectively aligns the light rays so that they are traveling parallel to one another when they exit the lens unit. As a result, all of the light rays strike the surface of the image sensor at a perpendicular angle. With coaxial lens units, light rays at the periphery of the lens tend to diverge from the optical axis and strike the image sensor diagonally, resulting in poor image quality at the periphery. With the new thin lens unit, light strikes all areas of the image sensor - from the center to the periphery - at a perpendicular angle, resulting in consistently high edge-to-edge image quality.
Fig.1 - Free-Shaped Prism Type Lens Structure & Light Path Fig.2 - Coaxial Lens Structure & Light Path
Fig. 1 -  Free-Shaped Prism Type Lens
Structure & Light Path
Fig. 2 -  Coaxial Lens Structure &
Light Path
Future Plans
In the future, Olympus plans to market a camera module that incorporates a free-shaped prism type thin lens unit, image sensor, flexible circuit board, and other related components. Test production at the Tatsuno Plant will begin in the spring of 2004, and full-scale production and sales of the module to cellular telephone equipment manufacturers are scheduled to begin in the fall. Annual sales of camera modules for camera-equipped cellular telephones are expected to reach ¥30 billion in three years.
*1 Free-shaped prism: An optical element that functions as a lens, and which is produced by combining asymmetrical, free-shaped lens and prism components into a single unit.
*2 Optical aberration: The deviation of light rays from an ideal path. The greater the aberration, the poorer the image quality.
*Olympus Optical Co., Ltd. was changed to OLYMPUS CORPORATION as of October 1, 2003.
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