Patent ID: 7125175

Claim:
A method of reducing the sensitivity of an optical device to post-weld drift, the device including a radiation emitter or detector and a lens system including a collimating lens, a focussing lens and a compensating lens, the method comprising the steps of: (i) directing an optical beam at the lens system in a first position, such that an output collimated beam is produced; (ii) adjusting the position of the collimating lens relative to a source of the optical beam to optimise collimisation; (iii) directing the optimised collimated optical beam at a focusing lens to focus the optimised collimated optical beam; (iv) adjusting the position of the focusing lens to focus the optimised collimated optical beam onto an output device; (v) welding the focusing lens in its adjusted position; (vi) positioning the compensating lens in the path of the focused collimated optical beam; and (vii) adjusting the position of the compensating lens to correct for any errors in setting the focusing lens.