1-PL-1-D20 UV fused silica Ball Lens, Ø2 mm

Ball lenses are used in endoscopy, bar code readers. Lenses are made of single piece of glass  and can focus or collimate light, depending upon the geometry of the input source. Ball lenses are rarely used for imaging, so that the relevant optical characterization revolves about determination of focal lenght. Given a ball lens with diameter D, made from glass with index nL, operated in air, the effective focal length, measured from the center of the lens, is easily found from (1). Since ball lenses are very "thick" lenses, the difference between EFL and BFL is significant and can be calculated from (2). The numerical aperture depends on the aperture employed; for an aperture diameter Da, where Da