Importance

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Abstract

The invention relates to an infra-red objective zoom system providing a high performance over a range of magnifications of from about 0.5 to about 8 times with a correction for temperature changes in a wide range it comprises only five optical groups of a total of seven lense groups (termed herein A to D). These are arranged in the sequence of A, a front singlet lens of positive power with a diameter larger than that of the other lenses abberation, B a negative optical element consisting of lenses B' and B'; B' being a negative lens having a dispersive factor larger than that of the other lenses, resulting in achromatization of the system; B' is a negative lens. Both negative lenses B' and B' have under-corrected spherical abberations, C being a positive lens, D being a positive auxiliary lens, being at a fixed distance respective lens A; E being a movable collimator of positive optical power, lenses B, C and E being movable respective fixed lenses A and D, said lenses transmitting in the 3.mu. to 12.mu. range. Lenses A to D define an objective and E a collimator (eyepiece). The movements of lenses B, C and E are according to a predetermined program which takes into consideration changes of temperature of the system.

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First Claim