Patent ID: 6900428

Claim:
A method of retrofitting an existing optical encoder of the type having a collimating lens with lens tube; the collimating lens comprising a unitary body having a first refracting surface and a second refracting surface that properly collimates light from a light source when at least one of the refracting surfaces is substantially interfaced with a medium of air; the lens tube being a part of the unitary body of the lens and substantially surrounding a circumference of the collimating lens such that a height of the lens tube is parallel to the propagation of the collimated light; and the lens tube having a crown end and a base end, the ends each lying in separate planes that are perpendicular to a height of the lens tube, the crown end being closest to the second refracting surface to protect the second refracting surface and the base end being closest to the first refracting surface, comprising the steps of: fabricating a first orthogonal cap from a substantially clear material that has a uniform thickness; and fixing the first orthogonal cap to one of the ends of the lens tube so that a first sealed air cavity is formed between the collimating lens and the first orthogonal cap, and at least part of the lens tube serves as a wall of the first sealed air cavity, the first sealed air cavity formed between the colliating lens and the first orthogonal cap enabling the optical encoder to function when submerged in a fluid.