why do some night vision goggles have 4 lenses PS31-4, Night Vision Goggle - USA G4, Auto-Gated/filmless, 64-72 lp/mm

why do some night vision goggles have 4 lenses PS31-4, Night Vision Goggle - USA G4, Auto-Gated/filmless, 64-72 lp/mmATN PS31 4 Night Vision Goggles The PS 31 Binocular Night Vision Device (BNVD) is a compact, lightweight, dual tube goggle to replace the legacy PS 15. In a sea of dual tube night vision goggles, the PS 31 is one of the smallest and lightest units by far. The PS31s can be outfitted with various levels of high performance US made Gen 3 image intensifier tubes. Working directly with U. S. Operators input, the PS 31 was designed to increase system

ATN PS31-4 Night Vision Goggles

 

The PS-31 Binocular Night Vision Device (BNVD) is a compact, lightweight, dual tube goggle to replace the legacy PS-15. In a sea of dual tube night vision goggles, the PS-31 is one of the smallest and lightest units by far. The PS31s can be outfitted with various levels of high-performance US made Gen 3 image intensifier tubes. Working directly with U.S. Operators input, the PS-31 was designed to increase system resolution, significantly reduce head borne weight, improve system of center of gravity, provide additional operational utility, and improve overall operator situational awareness and adding a 50 deg FOV for maximum visibility in the field. These tubes are auto gain-capable, allowing the system to adjust the brightness of their image as situations on the ground dictate. The PS-31 BNVD has independently pivoting tube housings that allow the operator to run the goggle in a binocular or monocular configuration. Using two tubes at once allows the eyes to create depth perception and increases the ease in maneuvering terrain and obstacles as well as operating devices such as control panels and door knobs. However, monocular configurations allow for ease in transitioning between various lighting conditions that often occur on the battlefield and cause operators to switch between night vision and weapon-mounted optics. Another benefit to the pivoting tube housings is the ability to mount the “flatten” goggle against the front helmet surface when stowed. The ability to pivot the tube housings against the helmet surface creates an overall lower profile, increasing operator safety and equipment life. 

User Guide:  ATN PVS-14/ATN 6015 operator’s manual (atncorp.com)
Specs:  ATN PS15 Specification Sheet (atncorp.com)        

TECHNICAL SPECIFICATIONS

• Generation - USA G4, Auto-Gated/filmless
• Magnification - 1 X
• Resolution - 64-72 lp/mm
• FOV - 50 °
• Total Darkness IR System - Yes
• Lens System - F/1.18
• Pro shield Lens Coating - Yes
• Range of Focus - 0.25 yard/m to infinity
• Diopter Adjustment -5 to +5
• Automatic Brightness Control - Yes
• Bright Light Cut-off - Yes
• Infrared Illuminator - Built-in 
• IR Indicator - Yes
• Low Battery Indicator - Yes
• Power Supply - 1 x 3V (CR123)
• Battery Life - 60 h – standard/ 300 h – with Battery Pack (optional)
• Finish - Matte Black, Corrosion Resistant Fibre re-enforces polycarbonate body
• Capability - Flip-Up On-Off, Side Flip-Up On-Off
• Environmental Rating - IP65
• Operating Temperature -59°F to +120°F / -51°C to +49°C
• Storage Temperature - -59°F to +185°F / -51°C to +85°C
• Dimensions - 4.5" x 7" x 3.5"/115 mm x 178 mm x 85 mm
• Weight - 1.27 lbs / 0.58 kg
• Available for Export - No - United States Only

What comes in Box.

* This product is subject to one or more of the export control laws and regulations of the U.S. Government and it falls under the control jurisdiction of either the US Department of State or the US BIS-Department of Commerce. It is unlawful and strictly prohibited to export, or attempt to export or otherwise transfer or sell any hardware or technical data or furnish any service to any foreign person, whether abroad or in the United States, for which a license or written approval of the U.S. Government is required, without first obtaining the required license or written approval from the Department of the U.S. Government having jurisdiction. For further information please contact ATN.