Field of View (FOV)
Field of View refers to the angle of view as measurable from the objective of a single tube/pod
The specification is written out in degrees of angle.
Many devices (for instance PVS-14, MNV-K, individual pods of DTNVS and PVS-1431 etc) have a FOV specification of around 40 degrees (compare this with human sight which has 90 degrees central view within a total of 120-140 degrees including peripheral vision).
The exact degree of FOV is possible to calculate if one knows the diameter of a tubes input window and various physical measurements and optical properties related to the lens employed by the device.
Overcoming FOV limitations
Naturally any field of view restrictions not equal to human baseline FOV is going to limit perception and awreness for the user and call for a number of strategies and techniques to compensate for this. The most obvious weakness is the loss of not only direct focal field of view but peripheral vision in low light conditions, making any night vision device arguably similar to a horses blinders. In any tactical or observational situation this is of course an immediate weakness and possible exploit.
This has led to the development of devices, accessories and lens kits that improve an individual IITs FOV or by changing the devices setup by either adding tubes or making them adaptable to different conditions and situations.
Panoramic devices or ”Quads”
An iconic and highly functional solution to the limitations inherent in any devices FOV is the panoramic quadruple tube setup. Originally designed for aviation purposes it has a quadruple array of tubes divided into two pods with two IITs each, one viewing straight ahead and the other offset to the side by a few degrees in order to achieve the smallest yet functional possible overlap of image. At the ocular end the eyebox lenses have been fused together, thus providing the user with a seamless blend of the overlapping circles. At correct interpupillary distance (IPD) setting the two parallel front facing tubes will provide a similar effect as when using a binocular device, with the added bonus of being able to either let the sideways facing tube images be observed for movement by the users peripheral vision or directly observed by glancing sideways.
The Panoramic NVG has also been further developed and ruggedized for use in dynamic environments outside of a cockpit. This latter device is known as Ground Panoramic Night Vision Goggle or GPNVG and features similar solution with two pods containing two tubes each.
Side-FOV devices, accessories and lenses
Some devices and lenses exceed the average 40 degree FOV and therefore lessen the tunnel-vision effect that users of night vision devices have to deal with in the field since observing any area that is not effectively an enclosed corridor requires constant panning around of the device and head.
Increased FOV on a device facilitates the users effort to cover any given area.
Such devices and upgrade lenses are marketed with users looking for an improved in both awareness and ergonomy in mind.
Panobridge
The pano-bridge is a dual monocular bridge that is engineered to widen the angle between each pod or monocular in a binocular setup, thereby increasing the compound field of view.
Non pano-adjustable bridges and binocular devices have a fixed angle between pods where they are parallel to each other and so the overlap of each pods own FOV is greater.
