Field of view
Field of view (FOV) is the extent of the observable world that is visible at any given moment. It is usually expressed in degrees, and for head-mounted displays (HMDs) it describes how much of the virtual or augmented scene reaches the viewer's eyes. A larger FOV lets the virtual world extend further toward the edge of vision, which can increase immersion, while a narrow FOV produces the sensation of looking through goggles or a tube. FOV is one of several optical characteristics, alongside resolution, eye relief and interpupillary distance (IPD), that determine how an HMD is perceived.
Human field of view
FOV targets for HMDs are usually framed against the limits of human vision. A single eye sees roughly 160 degrees horizontally, extending about 100 degrees temporally (toward the side of the head) and about 60 degrees nasally (toward the nose). When both eyes are used together, the horizontal extent of the visual field increases to roughly 200 degrees, with a central region of about 120 degrees where the two monocular fields overlap.[1] This overlapping region is called binocular overlap, and the stereo disparity within it is one of the cues the brain uses to judge depth.[2] Vertically the visual field spans roughly 135 degrees, about 60 degrees above the line of sight and about 75 degrees below it.[1] No current consumer HMD covers the full human field, so manufacturers treat these figures as an upper bound rather than a specification to be matched exactly.
Display FOV and camera FOV
In VR it is useful to distinguish two related quantities: display FOV (dFOV) and camera FOV (cFOV).
Display FOV (dFOV) is the angular extent of the image that the HMD's optics actually deliver to the eyes. Wide dFOV can increase immersion and induce presence, but it can also contribute to simulator sickness for some users. Two factors are commonly cited. First, the human visual system is more sensitive to flicker and motion in the periphery, which a wide display exposes. Second, a wide dFOV presents more overall visual input, and a larger mismatch between that visual motion and the signals from the vestibular and proprioceptive systems can provoke discomfort.[3]
Camera FOV (cFOV) is the FOV of the virtual scene as rendered by the graphics engine. If the cFOV does not match the dFOV, the virtual environment moves unnaturally in response to head motion. For example, a 5 degree rotation of the head can create a rotation of the virtual world that would normally require a 10 degree rotation in reality. This can cause discomfort and, over time, a maladaptive change known as vestibulo-ocular reflex gain adaptation.[3]
How HMD field of view is specified
HMD FOV is difficult to reduce to a single number, and published figures are often inconsistent. Several conventions are in use. Monocular FOV is the extent seen by one eye; binocular (or total) FOV is the combined extent of both eyes; and figures may be quoted along the horizontal, vertical or diagonal axis. A diagonal figure is numerically larger than the horizontal figure for the same optics, so a headset can appear to have a wider FOV simply by quoting a different axis.[2]
The FOV a person actually receives also depends on how the headset sits on the face. Because the lenses form an image that the eye must be close to in order to capture its full extent, the eye-to-lens distance (a function of eye relief, facial geometry and how the headset is worn) changes the effective FOV. Valve, which declined to quote a single FOV number for the Valve Index, states that for headsets above about 90 degrees a single millimetre of additional eye relief can reduce FOV by roughly 3 degrees, and that facial geometry varies by about plus or minus 6 mm between users.[4] For these reasons, independent measurements of the same headset differ from one another and from the manufacturer's claim, and any FOV figure is best read together with the conditions under which it was obtained.[5]
Measured field of view of common headsets
The table below lists manufacturer-stated figures alongside independent measurements. Measured values come from Road to VR (recorded with the TestHMD 1.2 tool at a 64 mm IPD at the closest comfortable eye relief)[6][7] and from a crowd-sourced measurement database compiled with an open-source tool.[5] Because measurement method, IPD and eye relief all affect the result, figures from different sources are not directly comparable and should be treated as approximate. Values are horizontal by vertical degrees unless noted.
| Headset | Manufacturer figure | Independent measurement (HxV) | Source of measurement |
|---|---|---|---|
| Oculus Rift CV1 | ~110 (nominal) | 87 x 84 | Crowd-sourced database[5] |
| HTC Vive / Vive Cosmos | ~110 (nominal) | 84 x 87 | Crowd-sourced database[5] |
| Valve Index | not specified by Valve[4] | 106 x 106 (Road to VR); 108 x 105 (database) | Road to VR / database[6][5] |
| Quest (1) | ~100 (nominal) | 95 x 92 | Crowd-sourced database[5] |
| Quest 2 | 96 x 90[8] | 90 x 92 | Road to VR[7] |
| Quest 3 | 110 x 96[8] | 104 x 93 | Road to VR[7] |
| PlayStation VR2 | ~110 (axis unspecified)[9] | not listed in cited measurements | --- |
| Bigscreen Beyond | ~102 (manufacturer) | 98 x 90 | Road to VR[6] |
| Varjo Aero | ~115 (nominal) | 84 x 65 | Road to VR[6] |
| Pimax 8K series | ~200 diagonal (nominal) | 158 x 105 | Crowd-sourced database[5] |
The discrepancy between marketed and measured values is largest for very wide headsets. The Pimax 8K series is marketed at around 200 degrees on the diagonal axis, while the same open-source tool measures about 158 degrees horizontally, and edge distortion reduces the usefully perceived FOV further still.[5]
Subtle dynamic FOV to reduce simulator sickness
Researchers at Columbia University used changes in FOV to combat simulator sickness. Ajoy S. Fernandes and Steven K. Feiner inserted a variable-transparency cutout in front of each eye, a so-called FOV restrictor, that subtly narrowed the user's FOV while they were moving through the virtual environment and restored it while they were still. In a study of 30 participants using an Oculus Rift DK2, the technique reduced reported VR sickness without lowering the participants' sense of presence, and most participants did not notice that their FOV had been changed.[10][11] The work, "Combating VR sickness through subtle dynamic field-of-view modification," was presented at the IEEE Symposium on 3D User Interfaces (3DUI) in 2016, where it received the Best Paper Award.[12] Comfort-oriented FOV reduction during artificial locomotion, sometimes called a "tunnelling" or vignette comfort option, has since become a common setting in VR software.
References
- ↑ 1.0 1.1 "Binocular Vision". https://entokey.com/binocular-vision-3/.
- ↑ 2.0 2.1 "Understanding Binocular Overlap and Why It's Important for VR Headsets". https://www.roadtovr.com/understanding-binocular-overlap-and-why-its-important-for-vr-headsets/.
- ↑ 3.0 3.1 "Simulator Sickness, VR Best Practices". https://developer.oculus.com/documentation/intro-vr/latest/concepts/bp_app_simulator_sickness/.
- ↑ 4.0 4.1 "Field of View, Deep Dive, Valve Index". https://www.valvesoftware.com/en/index/deep-dive/fov.
- ↑ 5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 "VR Field of View measured and explained". https://insights.infinite.cz/blog/VR-Field-of-View-measured-explained.
- ↑ 6.0 6.1 6.2 6.3 "Bigscreen Beyond Review, Promising but Incomplete". 2023. https://www.roadtovr.com/bigscreen-beyond-review-pc-vr-headset/.
- ↑ 7.0 7.1 7.2 "Quest 3 Review, A Great Headset Waiting to Reach Its Potential". 2023. https://www.roadtovr.com/meta-quest-3-review-mixed-reality/.
- ↑ 8.0 8.1 "Quest 3S vs Quest 3 vs Quest 2 Compared with Detailed Specs". https://www.roadtovr.com/quest-3s-quest-3-quest-2-specs-compared/.
- ↑ "Sony Announces PlayStation VR 2 Specs Including Eye-tracking, HDR, and 110 degree Field-of-view". https://www.roadtovr.com/sony-playstation-vr-2-announcement-psvr-2-specs-field-of-view/.
- ↑ "Fighting virtual reality sickness". 2016. https://phys.org/news/2016-06-virtual-reality-sickness.html.
- ↑ "Dynamic Field of View Restriction Makes Virtual Reality Less Barfy". https://spectrum.ieee.org/dynamic-field-of-view-restriction-makes-virtual-reality-less-barfy.
- ↑ Fernandes, Ajoy S.; Feiner, Steven K. (2016). "Combating VR sickness through subtle dynamic field-of-view modification". 2016 IEEE Symposium on 3D User Interfaces (3DUI). pp. 201-210. Template:Hide in printTemplate:Only in print.