What is dychroic filter?

A thin flat piece of glass along with a metal deposition in one of the surfaces applied into a high vacuum environment. There metal layer, only some atoms thick causes interference in the incoming light, letting a few frequencies pass as stopping others.

This frequency separation has the consequence of producing very vibrant colors and saturated.

Depending upon the deposition type, all visible light can be permitted to pass through, as stopping ultraviolet or infrared radiation. Actually there is a dychroic or interference filter to separate practically all frequencies into the spectrum.