A Guide to 360º Virtual Reality: Part 2 -Headsets

In our last blog, we covered the tools at the core of content creation: 360-degree VR cameras. Another core set of devices to consider are the viewing tools for 360 VR — the VR headsets or HMDs. In this article, we will cover some of the major headset features that will affect the viewing quality of 360 VR videos in different headsets. Since there are plenty of articles out there that talk about each headset individually(e.g Tom’s Hardware, Business Insider, etc.), we instead will focus on understanding what these features imply and what the future of VR headsets could potentially be.

Types of Headset

In the current market, VR headsets can be broken down into two categories: tethered and mobile. Some argue that there is now also standalone headsets, but we’ll get to that a bit later. Tethered headsets require the power of a VR ready computer. They tend to have better features and hardware, but are also more expensive. Mobile headsets, on the other hand, are more affordable and portable, and can be powered with a mobile phone. This however, binds their capabilities to the type of phone used with them.

Lens Type

One of the major factors that is commonly overlooked when determining a VR headset’s quality is the type of lens it uses. Lenses are responsible for bending light in a way that we can perceive, and our perception is greatly affected by how far away or close an object is. Our natural human lenses can only bend light so far, so VR headsets need to add lenses to help us see the display at close distances.

1 is a fresnel lens. 2 is a singlet lens. Picture taken from https://en.wikipedia.org/wiki/Fresnel_lens

The basic/standard lens, used by almost all mobile VR headsets, is a singlet. These tend to be thicker, heavier, and curved. They do the basic job of bending the light, but generally result in some sort of lens distortion or aberration. Higher-end headsets, on the other hand, use fresnel lenses. Fresnel lenses are thinner, lighter weight, and have concentric grooves that affect the sharpness and contrast when placed closer or further apart. They can also potentially increase the FOV. However, fresnel lenses are known to cause multiple new distortions like halo effects/lens flare, distorted rings, and light blooms. You can get a visual understanding of fresnel lenses from this video.

Field of View

Field of view (FOV) at the simplest level is pretty self explanatory: it’s the number of degrees the human eye can see. In VR, there are two types of FOV: the content FOV and the display FOV. Since this blog is about headsets, we will concentrate on display FOV, and the numbers you see will reflect that. Display FOV relates strongly to how close the lense sits to your face. Most devices will have a stock FOV that can be adjusted to increase the FOV by moving the lense closer or further away from your face. If you want to dive deeper and get into perception and 3D, FOV can be further expounded to include binocular and monocular FOV and you can read more about that here.

Pixel Density/ Screen Resolution

The dream for most VR users and headset makers is to reach retinal resolution, that is, a high enough pixel density that even those with perfect human vision cannot make out individual pixels at a normal distance. The golden number for retinal resolution is 60 pixels per degree.

However, since pixel density can be affected by other factors such as screen magnification, most VR headsets will only list their screen resolution, which is represented by the number of horizontal pixels x vertical pixels. The larger these numbers are, the better the resolution will generally be. Nonetheless, if you are still interested in getting an estimate for pixel density, you can use a simple formula: number of horizontal pixels in the display (per eye)/ FOV.

Refresh Rate

Refresh rate is another term that can be applied to both the content and the VR headset. In terms of the refresh rate for VR headsets, it refresh rate refers to the number of times in a second that the display updates, including the the repetition of frames. This differs from frame rate, which refers to the number of times a new frame is displayed in a second.The refresh rate is vital for a good user experience. A slow refresh rate is one of the culprits for VR sickness. When a refresh rate is too slow, the images on the screen do not match the rate at which the brain is processing the images, which causes the user to see glitches. The higher the refresh rate, the less latency a user will experience, the more realistic the content will be, and the less likely they are to get sick.

Bonus Features to Consider

Hardware platform: Do you need another device to run the headset? Most likely yes.

Adjustability: Being able to adjust the lenses will help you customize your FOV, sharpness, and general view. Adjusting the fit will help ensure it stays on your head as you move around.

Weight: Weight is a huge factor in comfort. The heavier the headset, the more of a toll it has on your movement.

Controls: How do you control and interact with things while using the headset? Is it gaze? Are there handheld controllers or a trackpad on the device?

Display Method: OLED or LED?

Tracking Type: We could write a whole article on this. We probably will, so check back soon.

VR Headsets Now and Into the Future

Tethered VR

  • PlayStation VR is known for eliminating the Screen Door Effect (SDE), which is when you see the grid lines between pixels, even though it has a lower resolution than the other devices. It does this by having RGB subpixels, which fill the space — its subpixel count far exceeds that of the other headsets.
  • Oculus Rift uses what they call a hybrid fresnel lens, which has the grooves of a fresnel lens, but is contoured to maximize the number of pixels in the FOV.
  • HTC Vive is currently the most popular of the tethered headsets. It is been consistently voted the headset of choice for developers, thanks to its room scale tracking, partnership with SteamVR, and controllers

Mobile VR

  • Google Cardboard is one of the easiest entry points to VR. It is low-cost and easily customizable, while still giving user a feeling of immersion.
  • Daydream View is unique in its form factor. It uses a lightweight fabric instead of plastic and has a super responsive remote.
  • Samsung Gear VR is the top selling VR device. It has a touchpad built in, and runs on Oculus.

Standalone Headsets and the Future of VR

Standalone headsets, those that don’t need to be powered by a mobile device or a computer, are the next hot thing in VR. Companies like Intel (Alloy), Oculus (Santa Cruz), and Google (Name TBD- partnered with HTC), have all released plans and various prototypes for these standalone headsets. Most likely these new headset will start out hefty and clunky, despite allowing more mobility. However, they will hopefully usher in the age of room scale VR without the need for intense setups.

Another standout device, though not standalone, is the StarVR headset. It is a tethered device, but has an extraordinary FOV of 210º, leaving users feeling super immersed. The new iPad Pro, mentioned in WWDC 2017, opens a few doors on what mobile VR headsets might be capable of it the future with its retina display and 4GB RAM.

With every passing year, VR headsets are improving and becoming more lightweight, affordable, and capable. Considering that hardware is currently one of the largest barriers to VR adoption, each new headset brings us closer to a world where VR is truly immersive. And that’s a future we at Visbit are truly looking forward to.

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