A new rod-lens relay system offering improved image quality

Traditionally, rigid endoscopes employed relay systems consisting of doublet relay objectives and singlet field lenses, until about 1960 when the rod-lens relay system was invented and led to the manufacture of endoscopes with much improved light throughput and image quality. The authors review these systems and describe the design of a new type of rod-lens relay system which employs an 'air-lens triplet' as the relay objective. This new system has greatly improved correction of astigmatism and field curvature, even when compared with the rod-lens relay system. Constructional data are given for the optical system of a laparoscope which uses the new 'air-lens triplet' relay system. The magnitude of the improvement in image quality, particularly for closed circuit television (CCTV) and photography, is demonstrated by a comparison of calculated modulated transfer function (MTF) results.