HoloLens - Much Ado About Field-of-View

Microsoft HoloLens is receiving overwhelmingly positive praise from press and social media, with one outlier in some reports: its Field of View (FOV).

In this article, I discuss the implications of FOV, the challenges of designing devices for a wider FOV, a number of business use cases where real value exists at the current FOV, and UX techniques to help compensate for it.

What is Field of View, or FOV?

FOV is the total vertical and horizontal angle extending out from the eye within which you see the world. This visible world can be the physical world, a virtual world, or a combination of the two. The total unobstructed binocular field of view of a typical person (not wearing glasses) is 130-135° vertical and 200° horizontal. Devices such as eyeglasses, binoculars, virtual reality (VR) and mixed reality (MR) devices all generally restrict our natural field of view. All else being equal, we tend to desire the widest FOV possible for devices we choose to use, because it most closely matches our natural view of the world, lets us see more, and requires the least amount of mental adjustment.

Although our full perception of our environment involves a wide natural FOV, in reality our brain focuses primarily on fovial vision which represents only 1.5-2° of our FOV, and secondarily on paracentral vision offering intermediate visual fidelity up to 8° of FOV. Visual acuity and color perception taper off rapidly beyond that. Basically anything beyond 8° is blurry, black & white, and most useful for detecting the motion of predators and other hazards.

Experiencing a more limited FOV is a matter of mental and behavioral adjustment. The primary reasons a device such as HoloLens requires a period of adjustment are:

• It requires more head movement and less eye movement compared to unconstrained eyesight to keep our fovial (central) vision within the FOV of the holograms.
• Holograms clip within a smaller FOV than the overall visual field available when wearing the device. We're simply not used to objects "disappearing" before it encounters the edge of our visual field.

The awkwardness of these two traits melt away after an adjustment period of learning to move your head more, building the missing mental context of your environment and grasping that holograms don't go all the way to the edges of your field of view. Well designed user experiences can help build and maintain helpful context of the virtual environment that extends all around you.

Given current technological limitations, wider FOV comes at the expense of other tradeoffs. Two popular VR devices, Oculus Rift and HTC Vive, offer a relatively wide FOV. For VR, this is key to creating the best possible fully immersive experience. Yet, offering this wide FOV in today's devices is typically at the expense of angular pixel density or other design compromises such as a cable tethering you to a powerful desktop PC.

Angular pixel density is key consideration. This is the number of pixels per degree of FOV. A lower pixel density results in an effect commonly referred to as the "screen door" effect because you can discern each individual pixel as if looking at the world through the holes in a screen door, like this close-up shot of a digital screen:

Unfortunately, seeing the individual pixels breaks the illusion of reality and presence. Lower pixel density also tends to make it more difficult to read text unless it is presented unnaturally large. For a tethered device, where a powerful desktop PC is providing the processing horsepower, pixel density is more a function of current display technology, cost and form factor, and less about available GPU power. For an untethered, full self-contained device, available GPU power, battery life and heat dissipation factor into the equation as well.

Angular pixel density is an area where HoloLens shines. Its angular pixel density is higher than any other VR/MR device on the market and the benefits are obvious. There is no screen door effect, text is easy to read, and holographic objects can look real enough to be mistaken for actual physical objects.

Choosing a particular target FOV when designing any optical device is a complex series of compromises between a variety of design choices such as battery capacity, battery life, form factor, heat management, cost, size, and weight. Any increase in FOV requires deeper compromises in other areas. Make it tethered, bigger, heavier and/or more expensive and any device manufacturer most assuredly can offer a larger FOV. There are some limitations of the physics of bending light that impact the widest FOV achievable with current waveguide technology, but ongoing technological and manufacturing innovations will most assuredly conquer those limitations. This limitation factors into cost and manufacturability. Here's an interesting Reddit article (with many links to other eye opening white papers) delving into this in more detail.

As I try more of the emerging palette of VR and MR devices, my belief continues to strengthen that Microsoft found a critical, viable balance of all these considerations for HoloLens given the current state of technology. As the industry innovates in optics, rendering technology and manufacturing processes, I’m convinced FOV will continue to improve rather rapidly.

Further, if I were told, for the next generation mixed reality device, that I had to pick between substantially improved GPU or greater FOV, I would choose better GPU. GPU performance would actually do more to improving the utility of HoloLens for business use cases than greater FOV, by allowing support for more complex 3D geometry. Thankfully, I suspect the next generation of devices will improve on both fronts.

I pose that the most pertinent question today is this:

“Can I solve real business problems and deliver tangible value with the current FOV, battery life, mobility and other design choices?”

The answer is a resounding “Yes!” for HoloLens.

High Value Use Cases

We and our clients are consistently finding real business value with today's HoloLens. Some of the areas where it's easiest to find tangible value are:

• skills training – practice a skill requiring manual dexterity and spatial understanding such as surgery or machine repair, and receive real-time feedback both during training and after the fact.
• scenario planning – review and plan a dangerous, expensive or otherwise difficult procedure beforehand in a virtual environment to identify concerns and improve chances of success.
• 3D FEA/simulation – experience 3D simulations of airflow, fluid dynamics, material stresses, mechanical systems and other normally invisible data.
• product design – visualize products in high fidelity and at true scale before they exist while avoiding the production of expensive and time consuming 3D prints, models or other props.
• remote collaboration – collaborate with remote teams to discuss projects that are 3D in nature, where everyone views, manipulates, tags and discusses 3D models in 3D.
• IoT – control intelligent systems throughout a physical environment. Visualize the analysis of collected telemetry data at the point in the controlled environment where the information is relevant.
• physical space planning – visualize a space and/or its contents before it exists, such as retail store layouts, interior designs and events.
• architecture – walk through architectural designs or modifications before they exist to accelerate design progress, or to help sell the vision before project sign off.
• assisted selling – visualize unique product features. Experience personalized products and product features where it is not feasible to stock all options in a retail venue.
• medical image analysis – visualize CT and MRI scans in 3D with the ability to see into the interior from any angle in real-time.
• assisted manufacturing – for products that are highly customized and/or built in low quantities, provide guidance and feedback during the manufacturing process to increase quality, reduce errors and train personnel.
• warehouse logistics – increase efficiency by guiding workers through optimized warehouse tasks with hands free access to all relevant information.
• data on a map – visualize any variety of geospatial data on maps in 3D, including animations of data changes over time.
• big data analysis – offer an additional dimension of data visualization over 2D screens to aid in identifying patterns and gleaning insights. True stereoscopic vision provides faster and deeper insights compared to 2.5D (rotations of 3D models on a 2D screen).
• storytelling – tell the story of the company, brand, product or service using interactive 3D and spatial audio.

This list of opportunities represents just the most obvious in this new era of mixed reality solutions. We expect many more to become evident over the next few years.

FOV in Binoculars

To give another perspective on FOV, consider binoculars. I dream of magical binoculars that are light, compact, high magnifying power, bright, and offer a really wide FOV. Unfortunately, there's a relationship between magnifying power, FOV, brightness, size and weight. The higher the magnifying power, the harder it is to also achieve a wide FOV without also increasing size and weight. Some people do choose to buy heavy, extra-wide-angle binoculars that are 2+ pounds and painful to wear around the neck. I have an amazing pair with electronic image stabilization that weigh almost 3 pounds and they make me smile when I use them, but more often than not, I actually choose to pack my compact binoculars on most trips. In the end, I find real value even with high-quality binoculars offering painfully small FOVs. The benefit is that they weigh only 12 oz and pack in the smallest of spaces. For many of us, a smaller FOV is actually the right choice to achieve the right balance of smaller size and weight. Lower weight and compactness trumps higher FOV.

Like binoculars, any increase of the FOV of the HoloLens, given the current state of technology at the time, would have required a bigger, heavier and/or more expensive device.

FOV in Eyeglasses

Over the years, I've chosen to wear progressively smaller eyeglasses, largely from a perspective of style – I like how I look in them. Coincidentally, the FOV of my current glasses are about the same as HoloLens and I realized that I was already gladly choosing to view my world through a HoloLens-sized FOV for the sake of fashion. My progressive lenses further reduces my FOV, forcing me to look through specific zones of the lens for different focal distances, requiring me to move my head more to keep what I am looking at in the right zone of my progressive lenses. Honestly, to this day, this can be annoying, but I'm okay with the balance of choices. When choosing glasses with a smaller frame (ie. smaller FOV) than before, there's a real adjustment period of a few hours or even days before the brain accepts the new reality. After that, the limitation becomes increasingly invisible and out of consciousness.

A side note – the adjustment to a device that constrains our FOV appears to be easier for those of us who wear eyeglasses. We're already accustomed to a smaller FOV. As a wearer of small progressive-lens eyeglasses, I move my head a lot more to experience my world than a person with 20/20 vision, yet I still find it a worthwhile compromise. 

Demoing HoloLens

For demoing HoloLens, this adjustment period to a constrained FOV presents a challenge. Unfortunately, any 5 or 10 or even 30 minute demo is within that initial adjustment period before the FOV becomes normal to the brain. For some people, this can leave an initial sense of disappointment. That quickly vanishes within a few hours with the HoloLens. Once you adjust to the FOV, you begin to truly grasp the real value it offers. This adjustment period poses a genuine first impression challenge. When we demo HoloLens to prospective clients, we try to allocate at least an hour of relatively unsupervised time on the HoloLens.

With that amount of time, almost everyone forgets about the FOV and leaves with an overwhelmingly positive impression of its value. I firmly believe that once a larger number of people experience HoloLens for more than an hour or two, that the popular opinion will be that HoloLens is an amazing experience that brings value to our lives, even at its current first-generation FOV. The reality is that after a few hours, or at most, days, the brain adjusts to whatever FOV we limit ourselves to, and it becomes normal for our brain.

HoloLens UX Tricks

With thoughtful application of a variety of UX methods, a UX designer can enhance the experience and accommodate design challenges that might be posed by the current FOV. Here are a few examples.

• Spatial audio – 3D spatial audio cues can let you know where something that wants attention exists in our surrounding even if not currently visible.
• Attention directors – Visual attention directors can appear within the FOV to subtly indicate the directions of points of interest and guide the use to them.
• Menus – Tag-along menus can stay just out of your FOV, yet always be available with a slight head movement.
• Anchoring – Anchor objects in specific locations in your work environment so you can get back to them easily by simply remembering how you organize your space and where you put those holographic objects. 
• Start small – Start the experience with small objects that fit the FOV, then transition with visual cues to larger versions of the object so the wearer is properly oriented and has enough context to fill in the blanks of what can't be seen.

We've found that thoughtful UX design can make a huge difference in usability and can make nearly any experience intuitive and informative.

Conclusion

Although greater FOV is desirable, it is not necessary for business applications to deliver tangible value with today's HoloLens.

I prefer the other (perhaps not so obvious) benefits that a smaller FOV affords me. For HoloLens, I prefer that it's an untethered device with great battery life, and offers high resolution holograms with a strong sense of realism and presence.

Food for thought.

Michael Hoffman, Co-founder, Object Theory

Twitter: m_the_hoff  |  LinkedIn: mthoffman  |  Web: objecttheory.com

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