Overhead projector triplet objective lens - has front lens meniscus of specified refractory index glass, dispersing middle lens, and rear one of specified focal length

摘要

The objective lens has the optical axis offset w.r.t. the centre of the objective aperture and/or that of the illuminating system. The triplet front lens (6) is a meniscus with a specified focal length and radius (r1), and is made of glass with a givenr efraction index and Abbe number. The middle diffusion lens (7) is independent and biconcave with specifided focal length, radius (r3) and of glass with given refraction index and Abbe number. Thus the part system formed by the two front lenses has a focal length of -76.8 mm +- 13%. The rear lens (8) has a specified focal length and a radius (r6). The rear lens can be adjusted for focussing. The entry pupil is at B = 12.8 mm + - 8% behind the first lens surface. USE/ADVANTAGE - For overhead projectors, withh low-cost mfr., small number of components, and easy focussing.