One of the key physical requirements of VR headsets of any type is to be able to adapt to the viewer’s individual facial and optical characteristics. A key component of this is interpupillary distance. The distance between pupils varies considerably from individual to individual with the extremes being 52mm and 72mm. As you can see in the image, if you are unlucky enough to be at the extremes of the range shown, you are not going to get a satisfactory experience from a fixed width head mounted display. Oculus attempts to address this by moving the virtual eyeballs to the correct setting when it renders the two images but there is no physical adjustment on the Oculus Devkit 1 and, to the best of my knowledge, the Devkit 2. From what I can see of Sony’s Morpheus, I don’t think you can adjust the lateral distance between the lenses either. I would like to incorporate this feature into my headset designs at some point, and, minimally, set the interpupillary distance for my headsets to be the average by default.
In order to adjust a head mounted display to the correct interpupillary distance, you need to know what your personal distance is. To that end I developed a series of physical measuring devices that culminated in the following prototype. The idea is that you can hold the device in front of your eyes and then slide the two holes closer or further apart until each pupil is centered in the hole as seen reflected in the image of the mirror. Once set the device can be placed on a table and the distance between the two eye holes measured.
It worked well when standing in front of a mirror in good light and was portable, but when I tried to use it on some volunteers it did not so work well. The usage model was unintuitive to them and without a stable mirror it was virtually impossible to align it correctly. I will build a new version that uses long parallel tubes with a light source at the end and perhaps incorporate a measurement scale or Vernier system in my next prototype.