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Optical filter features wideband phase retardation film

Posted: 10 Sep 2007 ?? ?Print Version ?Bookmark and Share

Keywords:optical low pass filter? wideband retardation film?


Epson Toyocom Corp. has developed a new optical low pass filter (OLPF) for digital cameras. The device features a new structure that enables the uniform separation of light rays across the visible spectrum.

Digital camera pixel counts continue to climb, and market demands for higher image quality are on the rise. An optical low pass filter is often provided on digital cameras to combat moir patterns. This lined pattern appears when two regularly spaced sets of repeating lines are superimposed. A moir pattern may appear in digital photos when a pattern in a subject is superimposed on the pixel array of a digital imaging device.

Conventional OLPFs employ a construction containing three quartz plates. Note that moir patterns occur when the geometric pattern of a photo subject changes at a narrower spatial frequency than that of the picture elements (pixels) of a CCD or CMOS sensor. By using the ability of quartz to separate light rays, the OLPF divides and regulates incident rays so that they strikes surrounding pixels.

The three-quartz plate system, however, does not provide uniform light separation characteristics at certain wavelengths, thus not all moir patterns are eliminated. Epson Toyocom's OLPF employs a new structure wherein a wide-band phase retardation film is sandwiched between a pair of quartz plates (Figure 1). This design provides uniform light separation at all wavelengths of visible light (Figure 2) and thus eliminates moir patterns across the visible spectrum. In addition, the new OLPF is also thinner and lighter than the conventional structure because it requires only two quartz plates, said Epson.

As a result, the new OLPF will further boost the image quality of digital cameras and enable them to be made thinner. The lighter weight of the new design also makes this OLPF ideal for CCD-shift camera-shake correction mechanisms and for functions designed to physically vibrate dust off the filter.

The new OLPF and other crystal devices will be on display at the at CEATEC JAPAN 2007, to be held at Makuhari Messe from Oct. 2-6.

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