Inside 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). Wavelength Isolation: Many applications, such as interferometry, require monochromatic sources. The creation of monochromatic light can be achieved by isolating natural peaks in source emissions (see illustration). 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. Lenses need to correct for this phenomenon to achieve good image quality. A filter can be used to create illumination that is more monochromatic, making the imaging lens design simpler and reducing costs significantly. Note: Monochromatic cameras cannot distinguish whether or not the whole image is a particular color (see contrast application below). These images were taken with a monochromatic camera and a relay lens (PCX pair). They illustrate the performance increase associated with filtering.