Joint Service General Purpose Mask JSGPM Presented by

Joint Service General Purpose Mask (JSGPM) Presented by: James R. Le. Blanc Vice President Fosta-Tek Optics, Inc.

Optical Plastic Lens Design Introduction • Optical Mechanics • Military Specification Issues • Quality Lens Design Issues

Optical Mechanics • Distortion • Resolution • Prism Correction • Optical Power

Distortion Non-uniform surfaces refract light away from the focal point. • Problems: – Distortion affect lens resolution – Causes Eye Strain – May cause nausea • Solutions: – – Mold construction Mold optical polishing Processing conditions Increases Resolution

Resolution • The ability of an optical system to distinguish between closely spaced objects. – The higher the resolution of a lens the greater amount of detail the wearer can identify. • Resolution is tested using standardized test targets. – Target consists of a series of graduated lines of various spacing.

Test for Resolution

Prism Correction Adjusts the perceived location of an image. • Adjust image position • Necessary for properly sighting a target

Optical Power • Measured in Diopters: – Related to the focal length of a lens. • Protective lenses are typically designed to have no power ( i. e. 0. 0 diopters). – No interference with the wearer vision. • Protective lenses are typically design to be worn over corrective lenses.

Military Lens Specifications • Specification Issues: – Optics must be design at the start of the project. – Industry input regarding optical design issues. – Critical tolerances on optical power of the lens must be firmly established. – Drawing and specifications must coincide properly. • Optical Zones: – Defining the critical area (Zone A). – Defining the non-critical area (Zone B).

Optical Zones • Zone A: – Critical area of the lens. – Should encompass visual field of the eye. – Highest optical quality requirements. • Zone B: – Non-Critical area of the lens. – Minor imperfection in optical quality acceptable.

Quality Lens Design • Optical issues should be addressed at the start of the design process. • Specifications should coincide with production drawings. • Critical zone size and location established properly. • Quality mold construction & optical polishing. • Correct processing techniques for minimum distortion and highest resolution.