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Optical Filters for All Occasions |
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Colour Imaging product lineColour Enhancement - SpectraPLUS Filters SPECTRAPLUS is a patented triple bandpass, interference filter coating that enhances colour and improves overall spectral performance. This filter benefits colour imaging systems as well as applications where the eye is the detector. The coating allows transmission of the three bands of pure colour - red, green, and blue - while blocking those intermediate wavelengths that distort the perception or recording of colour. It also eliminates wavelengths in the ultraviolet and near infrared which are detrimental to an accurate colour rendering and visual record. SPECTRAPLUS offers accurate hue, enhanced saturation, increased colour signal-to-noise, and a resulting improved Modulation Transfer Function (MTF). We suuply two SPECTRAPLUS coating designs - one is optimised for digital imaging sensors (XB29) and one is optimised for the human eye and film (XB30). All filters are finished to the highest imaging quality standards and are available in stock and custom sizes. SPECTRAPLUS is protected by U.S. patent #5,646,781.
XB29: Digital Imaging FilterOverview The SPECTRAPLUS XB29 filter is specifically designed for use with digital imaging systems and CCD-based cameras. These systems are sensitive to wavelengths beyond the visible which contribute no useful information for colour imaging. This version of SPECTRAPLUS blocks the crossover regions between blue/green and green/red centered at 490nm and 600nm respectively. To prevent IR saturation of silicon-based sensors, the coating provides a high degree of attenuation in the near infrared region, from 750nm to 1100nm. The XB29 also offers complete attenuation of ultraviolet A and B, and deep blue up to 430nm. These wavelengths may seriously impact apparent colour and reduce image sharpness. Applications SPECTRAPLUS XB29 has application in the optical systems of video cameras, remote sensing cameras, digital cameras for still photography, machine vision systems, and CCTV cameras. It eliminates the need for a red blocking filter, typical of CCD cameras. The XB29 is also appropriate for use in any color reproduction process based on digital sensor technology. These applications include pre-press scanners in the commercial printing industry, and desktop scanners and color copiers in the office products industry. As with all interference filters, the coating is most efficient across the entire field of view when the transmitted light is at an angle of incidence no greater than 30°.
XB30: Eye & Film FilterOverview The SPECTRAPLUS XB30 filter is optimised for applications where the human eye or photographic film is the detector. Colour imaging is enhanced with increased saturation, accurate hue, and improved contrast and resolution. This version of the SPECTRAPLUS filter has two stop band regions centered at 490nm and 580nm for blocking the prime colour "crossover" wavelengths between blue/green and green/red in the visible spectrum. The XB30 offers high attenuation of ultraviolet A & B. It also attenuates the near infrared in a band centered at 725nm. Applications SPECTRAPLUS XB30 has numerous applications in the photography, film, and video industries including: video, motion picture, and slide projection; photography, film, and video lenses; and enlarger lenses. In lenses the coating can be applied to lens elements or used as a discreet filter, both at slightly increased exposure time or lens aperture. In the architectural and theatrical lighting industries the filter can be used as a fixture filter or as a coating on bulbs or reflectors. It also has use in medical and dental lighting (where colour rendition is important). The coating improves "seeing" in ski goggles, sports eyewear, sunglasses, and sports optics especially in low light and flat light conditions. The filter is most effective in applications where the light is collimated, striking the filter at angles of incidence less than 30°.
Technical InformationAll sensors - human eye, film, and electro-optical - have limitations in how they "see" and record colour. Their receptors significantly overlap, as do the wavelengths for the three prime colours of light: red, green, and blue. A photon of light from within this overlap region can leave an incorrect signal on the receptor so that a green photon, for example, can be perceived or recorded as blue or red. SPECTRAPLUS blocks wavelengths between prime colours, as well as blocking UV and near IR. The human eye has optimal peaks at which it sees the three prime colours. Wavelengths between those peaks are "interpreted" as being a certain colour, demonstrating the subjectivity of human colour perception. Similarly, all still and motion picture films have three emulsion layers designed to detect wavelengths of the three prime colours. Overlapping wavelengths contribute confusing information to the recording of the scene's colour on film. Imaging sensors, such as CCDs, sxperience similar problems. These systems utilize prisms and filters to divide the spectrum into bands of colour which then activate individual pixels in a large or distinct array. Wavelengths of overlap between the bands cause confusion as to whether a pixel should be red, green, or blue. In addition to these regions of "crossover confusion" between the prime colors, ultraviolet and infrared wavelengths contribute confusing spectral information in certain sensors. For the colour image to be accurately recorded in sharpness, hue, and saturation, these wavelengths in the UV and IR must be attenuated as well. SPECTRAPLUS alleviates color registration problems. All optical imaging systems suffer from dispersive and resulting chromatic aberrations that limit the ability to record the color image of an object with precision. The ideal lens allows only a single wavelength of color to reach the sensor. Modern lenses use multiple optical glasses of different dispersion to permit sharp and accurate images at up to three wavelength bands. Lenses are designed to select the peaks of the three prime colors and focus them on a common image plane. As a result, wavelengths other than pure red, green, and blue are not well focused. Colour Separation FiltersColour imaging and measurement systems utilise colour separation filters as well as prisms to differentiate the prime colour wavelengths. Image capture systems divide light into red, green, and blue before reaching the detector. Image delivery systems recombine the red, green, and blue to form an image. In either case, system performance can be enhanced by carefully controlling the wavelengths and the areas of overlap. Systems which use prisms to control the spectrum can have enhanced performance using colour separation filters. Colour filters have application in colour imaging and reproduction systems such as analog and digital video cameras, digital still cameras, digital and video projectors, scanners, and copiers. They also have application in colour measurement instruments such as colorimeters and radiometers. For applications with demanding specifications we offer High Purity Colour Separation Filters and Sets with extremely high optical purity. These filters eliminate any overlapping wavelengths between colours.
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