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Liquid-Filled Camera Sees Like an Eyeball

Photonics Spectra
Nov 1998
Aaron J. Hand

When it comes to discriminating between various shades of black and white -- even picking out a dark figure lurking in the shadows -- the eyeball does a very nice job. Cameras, on the other hand, are somewhat lacking in their capabilities. 

Edward Kelley's liquid-filled camera mimics the eye to obtain high-contrast photographs. The prototype shown here is plugged into the electronics through the blue socket, and the mirror shows the high-contrast target. Courtesy of E.F. Kelley.

Veiling glare, or lens flare, reduces contrast and resolution because of stray light bouncing off various points in an optical system. It is less of a problem for the human eye because it is liquid-filled. So a physicist at the National Institute of Standards and Technology has designed a camera system that mimics the eye, filling the area between the lens and the charge-coupled device sensor with silicone oil.

With Edward Kelley's initial liquid system, contrast ratio -- a difficult, cumbersome measurement for existing instruments to make -- is almost 70 times better than the same camera without liquid. Eliminating the air and gas interfaces within a camera reduces the veiling glare, Kelley said.

Contrast ratio is used by the display industry as one measure of quality, because higher contrast can produce more realistic images. Measuring contrast ratio, however, typically involves complex calculations and image analysis, which is often an uncertain method, Kelley said. "Using a 35-mm lens, you might measure the contrast ratio at 50:1 when it's actually 250:1," he said. "Many people are not aware that veiling glare is such a problem."

Hector Lara, chief optical scientist at Photo Research Inc. in Chatsworth, Calif., is quite aware of the problems that veiling glare can cause. His company, which manufactures photometers and colorimeters, among other instruments, continually battles with contrast measurement, the biggest downfall in such instruments, according to Lara. Measuring contrast ratio is now done mechanically with baffling, he said, hindering the instrument with extra components.

Kelley's liquid-filled camera would enable the next generation of instruments for contrast measurements, Lara said -- smaller, simpler instruments with improved performance.

The growing market of digital cameras also could benefit from such a system. "A camera using this system would produce better pictures, with a wider dynamic range," Kelley said. "It could really change the way we think about pictures."

At this point, Kelley has produced just a preliminary prototype, but he hopes to have the next-generation prototype completed by the end of the year.

"As it gets developed, believe me, we'll be in there," Lara said.

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