Dichroic Lens

You know the drill: light hits glass, and suddenly a wavelength splits off as if by magic. That's dichroic — an optical coating that doesn't just reflect or transmit, but selectively decides based on color. Unlike normal mirrors or filters that work broadband, a dichroic layer reacts to specific wavelengths at an atomic level. The result: an ultra-sharply defined color separation that is indispensable in modern camera technology.

On set, you'll encounter dichroic filters in two contexts. First: in the prism system of 3-chip cameras — there, a dichroic prism splits white light into RGB and directs each color to a separate sensor. This is why such cameras deliver such clean color information. Second: in zoom lenses and premium lens constructions, where dichroic surfaces suppress internal reflections, thereby optimizing contrast and color accuracy. Some high-end cine lenses have multiple such coatings to minimize light loss and eliminate aberrations.

Practically, you'll notice a dichroic filter by the fact that it glows with color under oblique lighting — an iridescent violet or green, while the dominant color passes through. This is not contamination, but the design. In lighting design, some DoPs also consciously use dichroic filters as an effect element — for example, to filter out specific spectral components from hard daylight without sacrificing brightness. This works much more efficiently than thick ND filters with unwanted color casts.

Important: Dichroic filters are angle-dependent. If you change the angle of incidence, the spectral separation sharpness shifts. This is particularly relevant in prism systems — which is why the elements there are mounted with micrometer precision. For maintenance: these surfaces are extremely fragile. You don't clean them like normal lenses. Use an air blower, period. Cloths and solvents will destroy the coating.