NVG Aperture

When you use a night vision devices. The focus can only be set to a certain distances. While you set it to a far distances, the close object becomes hazy. On the other hand, when you set it to close distances, objects far away become hazy.

This devices can manipulated how much light enter the devices and let your night vision goggles to focus on objects on all distances, In an exchange for a dimmer image.