Marie-Maude de Denus-Baillargeon explains what an optic filter is.

An optical filter is something that allows only some part of the light to pass through, thus giving us only the information we need. Everyday examples of optical filters would be anti-glare glasses, or even sunglasses. These represent optical filters because they affect the way the light arrives at the detector, which in this case is your eye.

ASTROLab/Mont-Mégantic National Park

© 2006 An original idea and a realization of ASTROLAB of the National park of the Mount-Mégantic