Virtual reality headset Oculus Rift
Virtual reality headset: eye issues
The virtual reality caseque Oculus Rift is designed by Oculus RV company. It is a computing device connected to a computer, PC or Mac, and consisting of a display screen coupled with stereoscopic bi-oculaire system. Each eye looks a different image, through a dedicated eyepiece. The dimensions of the caseque are comparable to those of a diving mask, but promised here immersion requires no tuba or bottles: it is only Visual, possibly sound, but it seems yet total. From the first use of the caseque, we got the feeling to be transported into another world, to be spent through the looking glass. The virtual seems real, he's bluffing our sensations by the Visual realism provides this Visual dive into dimensional sort 360 universe. The adage "To see is to believe" ("Seing is believing") takes on a particularly concrete dimension.
This page is primarily devoted to the Visual aspects and optical challenges of the Oculus Rift (version DK2) virtual reality caseque, of which there are already competing models like the Samsung Gear RV, Google Cardboard, marketed in some countries.
These views of virtual reality devices offer countless opportunities to renew the field of the video game of the show, and democratize virtual reality. The equipped player of the caseque is no longer in front of a screen: he dives into the universe of the game, the action takes place all around him on 360 °, and it is possible to observe moving the head from left to right, from bottom to top, etc. The event viewer is no longer facing the stage where it takes place: a concert filmed in 3D and panoramic vision can be viewed with this type of caseque: This gives the wearer the feeling to be carried on the stage, in the middle of the musicians. It can be seen at leisure, turning his head, as he would 'naturally' if he was physically present among them. Once carried out the step of the acquisition (or creating) realistic content, it is possible to virtually visit but a very realistic exposure, fly over a landscape, or even attend since at home in a conference... as if we were there.
The computer connected to the caseque generates a video stream consists of pairs of moving images, to a refresh rate of 60 Hz. One of the images of each pair is meant to be seen by the right eye, the other by the left eye. The screen is the same as that which equips the Galaxy Note 3: technology is AMOLED, and its resolution of 960 × 1080 pixels per eye (a "half" format "full HD"). The images are calculated numerically or acquired (3D camera), so as to simulate the respective views of the left eye and the right eye. This allows the observer to collect the reliefunder the mechanisms that allows the Visual system to estimate the relative distance between apparent objects of the scene observed (stereo). The field of vision expanded (about 100 degrees) reinforces the impression of realism, but it is especially the constant monitoring of the movements of the head allowing the display "virtual universe" in which is virtually plunged the user who contributes most to the sense of immersion. The head movements are tracked by a device connected to the computer, and which records the information transmitted by a gyroscope and an accelerometer present on the caseque. This information is processed to return an image that should be displayed smoothly and with a possible shortest latency (currently estimated less than 20 ms) on the display (via a DVI port). The display of the caseque responds to the movements of rotation of the head, but also forward or back. This lag time is short enough with the version tested (DK2 + iMac) to avoid embarrassment or discomfort.
The right and left eye are composed of a simple biconvex asymmetrical plastic lens, which the Home object is located in the plane of the display screen. The light rays emitted by each of the dots on the screen (ex: pixels) are refracted through the eyepiece and returned to infinity; the eye perceives an image enlarged screen, whose observation (at least in monocular) is relatively comfortable - accommodation is not stimulated at the Emmetropic. The angle of observation is due to the short distance between the eye and the ocular (a few millimeters), the focal length of the eyepiece (approximately 50 mm), and the diameter of the eyepiece.
However, this system has some imperfections, which degrade in quality of use, which is damaging in terms of realism and performance. A biconvex lens of strong used as ocular vergence generates 'barrel' distortion, and chromatic distortion.
The particular interest of a caseque of virtual reality is that the image projected on the display screen can be "manipulated" for offset some of the limitations of the optics of the eye. Barrel distortion is offset by an ad-hoc deformation of... image that appears on the screen (without the eyepiece) barrel. This is perfectly logical under the reversibility of the optical path: remember that the screen is located in the space object, the eye of the user located across the eyepiece.
The same principle prevails for the chromatic distortion mitigation, related to the prismatic effects of the rays refracted by the edges of the eye lens. Here, the display generated by the Oculus Rift has fringes that correspond to the lateral shift necessary for the colourful radiation necessary for mitigation of chromatic aberration. In the previous diagram, if we consider the displacement of the rays from the screen, through the eyepiece, the presence of colored fringes to reconstitute a white light.
The following diagram and its expanded show the effect of the software compensation:
On the enlarged, the color fringes are visible:
Observed through the eyepiece, the compensation of chromatic distortion is noticeable:
Use of the caseque, ametropia, apply gap, Visual acuity
The caseque is provided with two pairs of (eye) lenses whose focal length is slightly different to compensate for a possible defective vision (spherical)myopia). The position of the lenses to the screen is also adjustable. Remember that the remoteness of the eyepiece on the display screen can not be executed beyond the focal plane, failing to produce an inverted image!
The correction of theastigmatism is not possible with the eyepieces, but wearing glasses of correction with the caseque seems possible (if the mounts are not too prominent). This is especially useful for the astigmatic strong and hypermetropia. The apply gap (average 64 mm) is managed in a software manner, and probably governs the distance from the center of the left and right images on the display screen.
The depth perception based on binocular vision: the history of strabismus, of amblyopia reflect the lack of binocular vision, and the use of a virtual reality caseque will not allow reached a disorder of binocular vision user to enjoy the stereoscopic effect.
Outside the optical quality of the eyepiece, the quality of the display is crucial to enhance the use of the caseque of virtual reality. The commercial magnification of a magnifying glass is equal to its vergence (in diopters) divided by 4. This quantity expresses the ratio between the size of an object seen at 25 cm and the size of the same object observed through the magnifying glass. The vergence of the eyepieces of the caseque Rift is close to 50mm (5 cm), either a vergence of 20 diopters, and apparent magnification of x 5. To provide a equivalent to that of the screen resolution display observed at 25 cm (which is one Galaxy Note 3), should be priori multiply by 5 this screen resolution: this could be obtained approximately by doubling the number of pixels in each line and each column (4K resolution)... This raises many technical challenges, in terms of memory, display, and autonomy for a caseque powered by a battery.
In conclusion, the experience of virtual reality with the caseque Oculus Rift is significant. In the future, the improvement of this technology is based on improving the optical quality eyepieces, and expansion of the definition of the images on the display screen. The use of a design of better optical quality eyepieces (ex: achromatic doublet, aspherical lenses of high factor, as with the eyepieces of telescopes for astronomical observation) should guarantee a better experience by preventing distortion and chromatic aberrations. Increase the resolution of the screen is an unavoidable prospect, because the improvement of the optical quality of the ocular isolated would that unmask its low native resolution against these conditions of observations. A curved screen offers an interesting perspective for addressing the problems posed by the conditions of observation on a broad field, and reduce chromatic and geometrical distortion.
Thank you very much Samuel Demeulmeester for making this possible test.