Applications for filters

Typical Applications for Filters
Filters can be used to attenuate light either evenly across a certain portion of the spectrum (neutral density, polarizing, retarders, etc.) or unevenly (ie., interference, dichroic, color). Typical applications for filters involve improving contrast or signal-to-noise ratio (imaging and non-imaging), isolating particular wavelengths (analytical chemistry and spectroscopy), and improving lens performance (usually imaging).

Contrast and S/N Ratio
One of the most prominent applications for filters involves increasing a system’s contrast or sinal to noise ratio (SNR). In imaging systems, this is extremely important because a monochrome CCD camera cannot distinguish different colors with the same greyscale. A filter can be used to increase contrast in order to differentiate objects of different colors.The proper filter needs to increase the detection of signal while reducing the detection of everything else. When determinig the optimum filter, match the filter’s curve to the detector’s spectral sensitivity, the source’s emission spectrum and the spectral profile of the background noise. Each of these affects how efficiently the signal is detected.

Wavelength Isolation
Many applications, such as interferometry, require monochromatic sources. This can be achieved by using a laser source or by isolating natural peaks in source emissions. The concept of wavelength isolation is commonly used in fields such as spectroscopy and analytical chemistry (substance identification through spectral analysis).

Boost Lens Performance
Different colors (wavelengths) focus through glass differently. For this reason lenses need to correct for this phenomenom to achieve good image quality. A filter can be used to create more monochromatic illumination, making the imaging lens simpler and reducing costs significantly.

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