The Opsin in humans that is excited by the short Wavelengths in the Visible Range (hence the “S” for short). The typical form has a Peak Wavelength at 420nm, which is a wavelength that excites blue/violet in Color Normals, hence the common colloquial name, Blue Opsin (or Blue Cone).

The opsin is encoded by the OPN1SW Gene on Chromosome 7. When the OPN1SW gene is missing (or altered enough to be inoperative), the individual exhibits Tritanopia. When this gene has a minor mutation (e.g. decreasing its sensitivity), the individual often exhibits Tritanomaly. However, these tritanomalous mutations do not enact a shift in the opsin’s Peak Wavelength like is common for the other opsins.