Optical lens assembly and optical measurement method

An optical measurement method comprising steps of:

• a) providing an object that is for emitting a light beam, a fastening unit, a lens unit that includes a casing, which has a light-incident side, and a sleeve unit that surrounds said light-incident side of said casing, that defines a light-receiving space, that includes a first sleeve which surrounds said casing, and a second sleeve which is connected to said first sleeve, and which is movable relative to said first sleeve, a length of said sleeve unit being adjustable, said fastening unit surrounding said sleeve unit and being operable to tighten said sleeve unit so that said sleeve unit is removably mounted to said casing;
• and
• b) operating said lens unit so that the light beam emitted by said object passes through said light-receiving space and is received by said light-incident side of said lens unit, said light receiving space protecting propagation of the light beam therein against disturbance caused by movement of air.