Four Thirds | About Four Thirds

·100% digital concept Digital-dedicated design optimizes performance of the image sensor. ·High mobility Compact design maximizes camera mobility. ·Open standard Ensures expandability and compatibility of products from different manufacturers.

To capture images, D-SLR cameras incorporate a device called an image sensor (CCD, MOS, etc.) that captures light in the form of electrical signals. However, since the image sensor’s characteristics differ from those of film, a lens optimized for film photography may perform poorly with an image sensor.
Developed explicitly to fulfill the potential of digital technology, the Four Thirds system is a new, open standard created with an eye to the future of D-SLR cameras. Since its introduction in 2002, this trend-setting standard has received worldwide recognition for its superior performance and enhanced compatibility.
The core design concept of the Four Thirds system is to facilitate optimization of the size, performance, and extendibility of digital cameras and lenses. In addition, a standardized lens mount allows photographers to freely combine interchangeable lenses and cameras from different manufacturers. This is the key feature of the Four Thirds system, the one that makes it possible to explore the full potential of digital photography.



	The biggest problems facing typical D-SLR cameras are the image degradation of peripherals and the appearance of ghosts and flares. Picture quality problems such as resolution loss, chromatic aberration, and shading in peripheral areas are particularly noticeable when a wide-angle type lens is used. Ghosts and flares are produced when the light reflected on the image sensor surface is reflected again on a lens surface.
	*The above data comes from our own comparative experiments and the effect may differ according to conditions. Both photographs above were taken using the same angle of view and F-number, but one was taken using a standard 35mm film camera lens and the other with a Four Thirds lens. A comparison of the images clearly shows flaring and ghosting in the picture taken with the 35mm film camera lens, as well as coma flare around the periphery and an overall lack of sharpness. The picture taken with the Four Thirds lens, on the other hand, does not have any apparent flares or ghosts and is uniformly sharp throughout the image plane.



	The image sensor in a digital camera can be compared to a “deep well.” You cannot see the bottom of the well unless you lean over it. In the same way, light inclined at an angle cannot reach the image sensor (i.e. the bottom of the well). Many of the current interchangeable-lens D-SLR cameras using traditional 35 mm film camera lenses are very susceptible to loss of sharpness, chromatic aberration, and shading of peripheral areas. Wide-angle type lenses are especially problematic since oblique light inclined at a large angle tends to enter the peripheral areas.
	With the Four Thirds system, the diameter of the lens mount exceeds the sensor size and the digital-dedicated lens design allows all the light (even on the periphery) to travel perpendicularly to the surface of the image sensor. The result is a sharp, clear image reproduction throughout the image plane. Linear propagation of light and the high imaging performance made possible by the digital-dedicated design are the biggest features of the Four Thirds lenses.

To maximize the performance of the image sensor, the camera must be designed so that the light is straight even on the periphery of even on the periphery of the image sensor surface. If a traditional 35mm film-size or APS-size image sensor is used, the only way to ensure that the light is passed through in a straight line to the image sensor is to increase the size of the optics. When the Four Thirds system was designed, special care was taken to avoid this problem and to achieve the optimum balance between high picture quality and compact size. The 4/3-type image sensor that resulted from this quest is where the Four Thirds system gets its name.
The foundation for the high picture quality of the Four Thirds system is the lens mount, which is about twice the diameter of the image circle. This extra headroom allows much more freedom in lens design and ensures sharp, clear imaging performance. Despite the compact size of both camera and lens, light still hits the image sensor directly even on the periphery of the image. The straight light path has also made possible a dramatic improvement in image quality.

The diagonal size of the 4/3-type image sensor is about half that of a 35mm film sensor. This means that the focal distance required to obtain a given angle of view is half that needed for a 35mm film camera. As a result, the optical system can be made much smaller. Moreover, because the effective aperture can be reduced without reducing brightness, the Four Thirds system makes it possible to design much brighter lenses. Thanks to this compatibility between compact size and large aperture, the potential for evolution of lenses is virtually unlimited. In other words, the adoption of the 4/3-type image sensor has made it possible to develop lenses that not only offer performance that surpasses almost anything achieved with traditional lenses, but are also compact and highly mobile.
For example, a Four Thirds telescopic lens equivalent to a 35mm 300mm lens can be implemented with a focal length of 150mm, and it can also offer wide aperture and high brightness corresponding to f2.0 while the maximum brightness available with a traditional lens was f2.8.
As you can see, the Four Thirds system is the ideal digital SLR system. By pursuing the optimum relationship between image sensor size and lens mount size, the Four Thirds system successfully combines high image quality and compact size. The potential of the Four Thirds system is further enhanced by exclusive software that supports all aspects of the image creation process from image exposure to editing and management of photographed data.

*	Details of the Four Thirds System standard are available to camera equipment manufacturers and industry organizations on an NDA basis. Full specifications cannot be provided to individuals or other educational/research entities.