Virtual reality headset lenses

Virtual reality headset lenses are lenses that take an image, typically from a flat display an inch or two away from the lens and bend the light so it comes into the eye at a different chief ray angle.

The lenses in a virtual reality head-mounted display (HMD) make possible to focus on the images produced by the displays that are very close to a user’s eyes. The lenses are placed between the screens and the viewer’s eyes, giving the illusion that the images are out to a distance where they can be viewed comfortably. This is achieved through the lenses in the VR HMD helping to reduce the least distance of distinct vision. It should be noted that if a user normally needs glasses or contact lenses to clearly see objects far away, he will need to wear the glasses or lenses while using the VR equipment.

Lenses in head-mounted displays

Figure 3. A high number of Fresnel lenses. (Image: VR Cover)

Figure 4. A lower number of Fresnel lenses. (Image: VR Cover)

Lenses are needed in VR head-mounted displays (HMDs) in order to bend the light, making it easier for our eyes to accommodate the incoming rays and correctly see the images generated on a display that is 1.2 to 3 inches from the user’s eyes. With the lenses, the images are perceived farther away than they really are. The intermediate lens bends light rays, reducing the divergence angle of light coming from the screen to a point where the eye can focus it (Figure 2).

The created illusion of an image that is farther away than in reality is called a virtual image. If the rays of light between the intermediate lens and the eyes are projected backward, they will intersect in a single point behind the VR screen (Figure 2). This is the reason why users can focus on the images from the VR displays that are so close to their eyes. They are not trying to focus on images generated very close to their faces but on virtual images that seems to be at a larger distance. The distance of the virtual images depends on the model of the HMD. In the Oculus Rift DK1, the virtual screens were infinitely far away while in the Oculus Rift DK2, they were about 4.5 feet away.

The HMDs can also use Fresnel lenses. Indeed, the HTC Vive uses this type of lenses, and the Oculus Rift CV1 has hybrid Fresnel lenses. These lenses are used to make the headset’s lenses thinner and lighter while maintaining the same function as regular lenses. Fresnel lenses have the same curvature than normal lenses but they are segmented (Figure 3). However, there are some compromises when using Fresnel lenses: firstly, creating lenses with many segments will result in a sharper image but some light will be lost that gets scattered at the lenses’ peaks (Figure 3). Secondly, Fresnel lenses with fewer segments will result in less scattered light but the image will not be as sharp (Figure 4).

Valve’s new lenses

On October 2017, Valve revealed new lenses for headsets compatible with SteamVR. According to Valve, these lenses improve VR experiences on OLED and LCD HMDs. On the press release, the company wrote that “the lenses, which are designed to support the next generation of room-scale virtual reality, optimize the user’s perceived tracking experience and image sharpness while reducing stray light. Valve is including the custom lens calibration and correction software within the SteamVR technology suite.”

Valve has clarified that the lenses will only be available for developers of SteamVR-compatible HMDs and not to the general public.

VR headset lenses

VR headsets such as the Oculus Rift DK1 and DK2 use biconvex nonequiconvex lenses, meaning they are convex on both sides, but each side has a different curvature from the other.

Biconvex lenses are ideal for positive conjugate image ratios from 0.2 to 5.

5X Packette Magnifier

• Bausch + Lomb 5X Packette Magnifier lens

The lens measures approximately 1 7/16" (36 mm) in diameter and has a 2" (51 mm) focal distance.

Injection molded PMMA lenses

Injection molding of PMMA eyepiece lenses involves heating PMMA pellets to about 130–180°C, injecting the molten material into a mold (often with multi-cavities for efficiency), and cooling under controlled conditions.

Lenses for DIY Oculus Rift

7.2" screen

Condenseur 51mm Pyrex http://www.fresnels.fr/achat/produit_details.php?id=19&PHPSESSID=a7e9759040a3c8734143cba782944cdd

5.6" screen

Aspheric lenses

5x pocket loupe magnifier with Aspheric Lens

• http://www.ebay.com/itm/5x-pocket-loupe-magnifier-with-Aspheric-Lens-/251148139033?pt=LH_DefaultDomain_0&hash=item3a79987a19
• http://www.magnifier.com/aspheric_magnifiers.htm
• 2" / 5.1 cm focal distance
• 50.00 mm lens diameter

LEEP-like lenses

DCX Lens - 62.8mm dia. x 72.4mm FL http://www.anchoroptics.com/catalog/product.cfm?id=268&iid=20087 PCX Lens - 43mm dia. x 77mm FL http://www.anchoroptics.com/catalog/product.cfm?id=253&iid=21253

Phones and tablets

UltraOptix SV-2LPLED 7X Aspheric LED Lighted Magnifier http://www.amazon.com/UltraOptix-Powerful-ASPHERIC-Lighted-Magnifier/dp/B0054H1XYQ

Tablets

UltraOptix SV-3LPLED 4X Aspheric LED Lighted Magnifier http://www.amazon.com/UltraOptix-Round-Magnifier-Power-SV-3LPLEDSV-3LPLED/dp/B0019NA0S4