Joint Service General Purpose Mask JSGPM

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Joint Service General Purpose Mask (JSGPM)

• Presented by James R. LeBlanc
• Vice President
• Fosta-Tek Optics, Inc.

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Optical Plastic Lens Design

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

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Optical Mechanics

• Distortion
• Resolution
• Prism Correction
• Optical Power

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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

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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.

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Test for Resolution
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Prism Correction
Adjusts the perceived location of an image.

• Adjust image position
• Necessary for properly sighting a target

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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.

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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).

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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.
  

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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.