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681 - ICAS 2002 CONGRESS Optical Design of Two Field of...

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ICAS 2002 CONGRESS . 681.1 Optical Design of Two Field of View Infra-red Objective in 3-5 Micron Band for Focal Plane Array Detector M. Hammad Asghar Optical Design Group Advance Engineering Research Organization E-5, Officer Colony, Wah Cantt.47040. Pakistan. e-mail: [email protected] , mailto:[email protected] Keywords : Field of View (FOV), Modulation Transfer Function (MTF), Aperture Stop, Exit Pupil Abstract An easy and simple approach has been used in designing an objective with two fields of view working in 3-5 micron band. The field of view (FOV) in narrow mode is four degrees whereas field of view in wide mode is ten degrees giving a magnification of 2.5X. Priority is given to the use of conventional lens materials to make the design simple and practical. Use of aspheric and diffractive surfaces have been made to reduce the total number of elements in the design, and also to reduce the magnitude of the aberrations to an acceptable level. Four elements are used in narrow field of view mode and additional two element used as a clip-in group are used to change the field of view from narrow to wide field of view. Making a total number of six, in all. The performance of the objective is reasonably good keeping in view the number of elements used in the design. The performance is reasonably close to diffraction limit as exhibited by modulation transfer function (MTF) curves, and spot diagrams at different field positions. The design can be used for commercial as well as military applications. 1. Introduction In this paper an attempt has been made to explain the design of a 2 field of view objective for a focal plane array based system working in 3-5 micron band. The fields of view are narrow and wide. Narrow field of view design comprises of four elements where as wide field of view design has six elements. The field of view change mechanism has been proposed to be a clip-in group which when inserted into the objective changes the field of view from narrow to wide. When removed out, switches back to narrow mode.
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