Only allow the passage of light with specific characteristics (for example, light of a specific wavelength) and block or philtre all other light. Optical philtres are widely used in photography, optical devices, and lighting. When attached to a lens of a camera, telescope, microscope, or other device, lens philtres philtre the light supplied to the device. Most lens philtres are optical philtres that philtre light based on wavelength or polarization, but some create a soft effect or ray systems.