Darren's apartment was filled with holograms. A giant virtual globe stood in the middle of the room, spinning gently on its virtual stand. A holographic dog lay on the carpet, wagging its holographic tall. A Skype window hung on the wall. And an adorably cartoonish robot floated above the coffee table, cocking its head to one side and then the other.

Sitting down at the coffee table, Darren said he was planning a trip to Hawaii. That's why a virtual Maui sat on his end table—little holographic numbers showing the latest Maui temperatures. Then he turned to a video window on the wall in front of him, and with wave of a finger, he started a Tom Cruise movie. But he didn't watch it on the wall. He said "Follow me," and the video trailed him across the room.

When you wear the device—as opposed to viewing the holograms via a movie camera equipped with very different hardware—your 'field of view' is significantly smaller.

That's what you witnessed if you were among the thousands who gathered in a vast auditorium at San Francisco's Moscone Center on Wednesday morning. Darren's apartment was a set, arranged on a stage at the front of the hall, part of a nearly three-hour presentation from Microsoft at the company's annual developer conference. And Darren didn't have a last name. He was Microsoft's way of showing off HoloLens, the holographic headset it first unveiled early this year.

Darren was wearing the headset, and as he moved around the room, a camera captured not only his actions but the holograms viewable from the device. The camera, you see, was equipped with its own HoloLens-like technology, and it fed the entire scene—reality and virtual reality—to giant screens around the hall. It was a compelling demo. You can see it here—and listen to the audience cheer as the Tom Cruise movie follows Darren. But the demo wasn't quite what it seemed.

A Narrow View

At the conference, Microsoft also gave personal demos, letting select coders, press, and analysts try the HoloLens. It even let them build simple holographic applications for the device. These demos were also impressive. But the experience didn't quite match the impression you get from Darren's apartment. When you wear the device—as opposed to viewing the holograms via a movie camera equipped with very different hardware—your "field of view" is significantly smaller. You only see holograms in a slim area in front of your eyes—an area that spans about 35 to 40 degrees horizontally, according to Brian Blau, an analyst with research outfit Gartner, who received one of the demos.

However impressive a technology may be at first sight, that impression isn't quite the reality. You are not Darren.

In other words, your apartment may be filed with holograms, but you have to work to get your head in a place where you can really see what you want to see. "The effect is that you only see a small picture of a virtual world," says Blau, who has a long history in virtual reality, having founded an influential VR company called Intervista in the early '90s. "The narrower the field of view, the harder you have to work—just in terms of figuring out how the image fits into what you're doing."

For Blau, this indicates the device will work well in only a limited number of scenarios—at least in the short term. Microsoft is billing the headset as something that can handle everything from games and videos inside homes to product design inside businesses. But in the beginning, Blau says, its scope will be far smaller than Microsoft indicates. (Asked about the device's field of view, a Microsoft spokesperson said: "We are not discussing final specifications at this time.")

Virtual Unreality

The discrepancy between Microsoft's two demos highlights a larger issue with the release of new technologies in this age of breakneck innovation—particularly with the new virtual reality technologies spilling into the market from so many sources, including Microsoft, Facebook, Google, and startups like Magic Leap. However impressive a technology may be at first sight, that impression isn't quite the reality. It doesn't quite match what it's like to use something on a daily basis, without a company holding your hand. You are not Darren.

Today, it's easy to say that HoloLens will change the world, as many are. "We're extremely intrigued by it," coder Michael McCurrey told us last week, referring to his company, Ping Golf, which could potentially use HoloLens in designing golf clubs. "It could really revolutionize our business." But at this point, it's hard to understand what it will do even in your own living room. McCurrey hadn't received the personal demo.

'The team is clearly iterating on it quickly in a rush to get something out for folks to experiment with.' IDC Analyst Al Hilwa

After all, the device is still in flux. The hardware Microsoft demoed for press and analysts in January is different from what it showed last week. "HoloLens is amazing technology and may well be the basis of something that will be mainstream in gaming, entertainment and industrial settings 15 years from now, but today, I still this is [as] 'in the labs,'" says IDC analyst Al Hilwa, who also received a demo this week. "The team is clearly iterating on it quickly in a rush to get something out for folks to experiment with."

In short, some skepticism is required. And the same thing goes for the Oculus Rift, the virtual reality headset now under the aegis of Facebook. The Oculus offers a much wider field of vision than the HoloLens, but it suffers from other limitations—particularly if you try to turn it into more than just a gaming device, as Facebook is trying to do.

Facebook bills the Oculus as the future of social networking. But as powerful as it is today, the gap between the device and Facebook's ultimate vision is enormous—as the company acknowledges. One of the biggest issues—as with all these devices—is that people may not want to spend their time hardware strapped to their faces.

Like A Dream

Microsoft has built something that captures the imagination. Judging from a brief demo—about 90 minutes—HoloLens not only creates holograms but lets you manipulate them with relative ease, using not only the wave of a finger but the look of an eye or a short verbal command. It can attach sound to these holograms, so that they get louder when you're close to them and quieter when you're farther away.

But don't expect Darren's apartment. That limited field of vision means that in order to experience a full hologram, you have to move your head—and maybe even your whole body—to find what you want. And it means some holograms will work better than others. The general rule is that you must be "farther away" from a digital image in order to see it in full. This means it might be easier to, say, view a tiny model of an entire city than to view the model of a single building up close. As designer Barry Threw said on Twitter: "HoloLens is about the smallest possible straw you can suck an AR experience through. It's like a Ferrari with a keyhole for a windshield."

You won't quite understand this phenomenon until you try the device yourself. But there's a cautionary tale that can help you understand. When they first saw Google's augmented reality headset, Google Glass, many were sure it was the future. And now they aren't so sure. The device hasn't really changed all that much. It just didn't work quite like we expected.