To provide a liquid agent for optical instrument which can satisfactorily disperse particles in liquid even when the particles are not subjected to specific surface treatment and can form a thin film excellent in light transmitting property at a relatively low temperature, to provide a method for producing the liquid agent for optical instrument, and to provide a method for manufacturing the optical instrument having a process of applying the liquid agent for optical instrument.

The liquid agent for optical instrument comprises particles containing calcium fluoride, wherein the average particle size of the particles containing calcium fluoride according to a dynamic light scattering method falls into the range of 1 to 20 nm. The method for producing the liquid agent for optical instrument comprises a process of mixing at least one calcium ion supply compound (A1) selected from a group consisting of calcium glycerophosphate, glucose-1-phosphate calcium and glucose-6-phosphate calcium and a fluorine ion supply compound (B). The method for manufacturing the optical instrument comprises a process of forming a coated film made from the liquid agent for optical instrument onto a base material of the optical instrument.