Abstract: The ultra-high vacuum telescoping fiber optic feedthrough apparatus comprises a first tubular section having thereon a mounting flange, a quartz window aperture, and a collimating lens means. The second tubular section being in sliding contact with the first tubular section has a focusing lens means mounted therein. A third tubular section being in sliding contact with the second tubular section has mounted therein a fiber optic cable holding means. In order to provide adjustability between the various sections a first adjusting means being a micrometer screw is mounted onto the first and second sections and a second adjusting means is mounted onto the second and third sections whereby fine adjustment in translational movement is achieved so that the signal-to-noise may be maximized when observing an optically luminescent source such as a plasma formed during laser deposition.