Joint Service General Purpose Mask (JSGPM)

Presented by: James R. LeBlanc 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

• Problems:– Distortion affect lens resolution

– Causes Eye Strain

– May cause nausea

• Solutions:– Mold construction

– Mold optical polishing

– Processing conditions

– Increases Resolution

Non-uniform surfaces refract light away from the focal point.

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

Test Target

Sample Lens

Telescope

Prism Correction

• Adjust image position

• Necessary for properly sighting a target

Adjusts the perceived location of an image.

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.