Excerpt - used with permission from militarymorons.com
- One of the issues that users of Night Vision Goggles (NVGs) or Night Vision Devices (NVDs) will be familiar with is transitioning back and forth between near-far focusing. NVGs like the PVS-14 and PVS-7 shown here can be focused from about 6" to infinity by rotating the objective lens at the front, but frequent refocusing is needed if you need to see both near and far as the depth of field is quite shallow. When going from outdoors into a building or structure, if the NVG is focused at infinity, anything under about 25-30 feet becomes out of focus. The closer the object, the more out of focus it will be unless the NVG is refocused. Everything inside a room is quite blurry if the NVG is focused at infinity. The Hoplite from Phokus Research Group is a device that installs onto the NVG that deepens the depth of field, allowing more to be in focus at different distances. This decreases the need to refocus as often, and enables the user to leave the NVG focused at infinity for most far and medium distance tasks. It replaces the dust cover and sacrificial lens. Phokus Research Group was founded by a former military end-user and the company's primary mission is to partner with Soldier inventors for the purpose of protecting, developing and commercializing their ideas.