OBJECTIVE WITH DISCRETE CHANGES IN FOCUS LENGTH FOR WIDE SPECTRAL RANGE Russian patent published in 1996 - IPC

FIELD: optical instrument engineering. SUBSTANCE: objective has four components. The third and the fourth ones are mounted for introducing and rejecting these components out of optical circuit for making changes in focus length. The first and the second components provide focus length being equal to 449.22 mm and narrow field of view mode. To provide focus length of 117.41 mm, i.e. wide angle field of view mode, the third component is introduced between the first and the second ones; the fourth component is introduced behind the second one. The first component has single positive and negative lenses and one double-glued lens, formed by biconcave and biconvex lenses. The second component has positive and negative menisci turned with their concavities to each other. The third component has biconcave lens and positive meniscus turned with its convexity to object. The fourth component has biconvex lens, double-glued lens formed by negative and positive lenses, and positive meniscus turned with its convexity to object. EFFECT: improved efficiency of operation. 9 dwg