With the announcement of Rift S earlier this month came the revelation that the headset would not include the ability to physically adjust the distance between the lenses in order to align with the distance between the user’s eyes (also known as IPD), making the headset less adaptable to those with IPDs further from the headset’s nominal setting. We reached out to Oculus to understand the officially supported IPD range for Rift S, Quest, and the company’s other headsets, as well as their field of view.
In a conventional VR headset, the ideal scenario for comfort and clarity is to have each of the user’s eyes aligned with the optical center of each lens, and to have the optical center of each lens aligned with each display. This can be challenging because adult human IPD can range from ~50mm to ~80mm (with a normal distribution centering around 63mm).
Image courtesy ‘Variation and extrema of human interpupillary distance’
“Mean IPD is statistically significantly different between the two genders, between certain racial groups, between near and far viewing, and between certain age groups. Mean and median IPD for the adult human population both appear to lie somewhere near 63 mm. With regard to extrema: the vast majority of adults lie within the range 50 to 75 mm.”
In an effort to cover the IPD distribution from the 5th to 95th percentile of the population (the vast majority) the original Oculus Rift (also known as CV1) uses two separate displays to which each lens is affixed, along with a mechanism that allows the distance between the lens/display assemblies to be adjusted from 58mm to 72mm, Oculus says.
The Rift S, however, uses a single display to which both lenses are fixed, which means the actual distance between the lenses cannot be adjusted. Oculus has confirmed that Rift S will support a software IPD setting, which will adapt the rendered image for the user’s IPD. And while the software setting can improve the perceived scale of the rendered image, it can’t account for clarity or comfort issues which come with not looking through the optical center of the lens.
Official IPD Range of Oculus Rift S, Quest, Go, & Rift
Image courtesy Oculus
The removal of a hardware IPD adjustment on the Rift S has prompted questions about which IPD ranges Oculus considers suitable for the headset. We asked to company to confirm the IPD details of each of their headsets and received the following:
Rift
Adjustable lens IPD: 58–72mm
“Best for users between 56mm and 74mm”
Rift S
Fixed lens IPD: 63.5mm
“Best for users between 61.5 and 65.5mm
Go
Fixed lens IPD: 63.5mm
“Best for users between 61.5 and 65.5mm
Quest
Adjustable lens IPD: 58–72mm
“Best for users between 56mm and 74mm”
The company prefaced the figures with the following:
“It’s worth noting, of course, that perception and comfort will vary person to person and depend on anatomy, and some people may have a higher tolerance for the experience (for example, if they fall outside ‘best’ range, they could still use and enjoy the headset).”
Sweet Spot of Oculus Rift S, Quest, Go, & Rift
Image courtesy Oculus
From the figures provided by Oculus, it’s clear that the Rift and Quest share the same hardware-adjustable IPD range, while the Rift S and Go share the same fixed IPD. The information also appears to indicate what Oculus considers the size of the ‘sweet spot’ of each lens, the region of greatest lens clarity which provides the “best” viewing experience—for all four headsets, the sweet spot would be 2mm wide.
However, this doesn’t jibe with suggestions that the sweet spot has been improved with the newer lenses used in the Rift S, Quest, and Go. Granted, ‘sweet spot’ is not a precisely defined term; clarity may have been improved within the 2mm region, even if the region itself was not meaningfully expanded. We’ve reached out to Oculus for more info.
Unlike any of the other Oculus headsets, the Rift S includes a smooth eye-to-lens distance adjustment which will enable a more dynamic sweet spot along the z-axis, making it easier to achieve optimal field of view, and also helping to accommodate those with glasses. Oculus Go includes a glasses spacer which changes the eye-to-lens distance but only between the nominal value and the value achieved with the glasses spacer.
Field of View of Oculus Rift S, Quest, Go, & Rift
Image courtesy Oculus
On the field of view front, Oculus has long shied away from offering specific measurements (presumably because they are somewhat dependent on the facial structure of each user). The company was only willing to provide some vague, relative comparisons:
Rift FOV:baseline
Rift S FOV: “slightly larger than Rift”
Go FOV: “slightly larger than Rift”
Quest FOV: “equal to Rift”
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Following the reveal of the Rift S and its lack of hardware adjustable IPD, Oculus founder Palmer Luckey, who left the company back in 2017, said that the lack of hardware-adjustable IPD on the Rift S means he won’t be able to comfortably use the headset, and further expects that its IPD wouldn’t be suitable for about 30% of the population. Oculus didn’t respond to a request for comment on Luckey’s claims.
Back in 2015 however, ahead of the launch of the original Oculus Rift, engineers who designed the headset spoke about why they felt that supporting a wide IPD range was a key design goal, and the importance of being able to customize the IPD to fit each user.
The most important thing in terms of your comfort is getting optics right and getting the fit on your head right. The fit on your head includes things like ergonomics and also the way the weight is distributed. […]
You have two eyes, we have two screens [on Rift CV1]. Getting the right depth perception and focus is really important to get the maximum comfort for each person. Ergonomics is really crucial. When we’re talking about ergonomics, we want to fit everyone from the 5th percentile female, all the way up to the 95th percentile male, with one design. This is really, really tough. And if we get this wrong it won’t be comfortable for everybody. The Rift really needs to fit you, all of your customers, the whole community. […]
The Crescent Bay [pre-Rift] prototype didn’t do [IPD adjustment]. This is a really important feature on the Oculus Rift headset. Our problem as engineers is to get this [to be] a really smooth, easy adjustment, and also not to add too much weight or complexity. […]
The goal is to create better stereoscopic view, to create better depth perception, and better 3D.
Indeed, the engineers noted the challenge of making a headset with a hardware IPD adjustment that doesn’t add too much complexity to the design. Four years later, the perceived importance of the feature seems to have shifted as Rift S and Go have sacrificed their hardware IPD adjustment ostensibly to minimize complexity and cost.
Ergonomics—the physical fit of the headset—are also a critical factor. With a sweet spot tolerance potentially as small as 2mm, a headset must be able to comfortably rest in a very precise position on the user’s head in order to achieve good alignment, and it ideally should stay there for the duration of the VR session.
Other major headsets on the market have used a fixed IPD approach for years—notably PSVR and all of the Windows VR headsets—though they have not been without their own complaints.
A fixed IPD would not be problematic on its own except for the fact that it’s challenging to achieve a large sweet spot (the region of greatest lens clarity) with the simple optics used in conventional VR headsets.
