Varjo XR-3 Hands-on: Varjo’s Headsets Keep Getting Better, Even as They Get Cheaper

From valve’s Alan yates (originally posted on Reddit in relation to the Vive gearvr lens mod):-

“frensel lenses were specifically designed to minimise some dynamic distortions that we know can cause discomfort and motion sickness. The frensel lenses were not selected for low mass, low cost, hiding subpixel structure, filling SDE or any of the other crazy conspiracy theories I have read. They were the only practical lens technology for hitting the overall set of optimisations we wanted, especially minimising eye-position dependent distortion with a single element. They are not “cheap” lenses and need special equipment to make well. They are lower mass than the “equivalent” non-frensel profile lens, but that is mostly a happy coincidence, if a conventional lens could achieve the same performance in the axes we care about we’d happily tolerate the small mass increase for the reduced stray light and easier moulding. Our goal was to have lenses that worked well for everyone, from the least sensitive to the most easily nauseated. Some people just don’t perceive pupil swim, at least not until you tell them what to look for, and some people once they see it can’t unsee it and it ruins all HMDs with swimmy optics forever for them. Most concerning is that swimmy HMDs cause nausea at an almost subconscious level, you don’t need to perceive it for it to make your experience using the HMD unpleasant.

We also knew using frensel would mean accepting more stray light (aka “god-rays”) and would make the lens much, much harder to manufacture. It is technically difficult to make frensel lenses with low stray light by injection molding, you also have to be careful about spatial frequencies and a bunch of other important details. The Vive panels are brighter than other HMDs so we actually did quite well to keep the stray light to the levels you experience in the Vive lens. This is one of the many knobs HMD makers can use to deal with the various trade-offs in the optical system; turn down the brightness, soften the contrast, adjust the lens MTF, reduce the FOV, shrink the eye-box.

There were a lot of design compromises in the Vive lens. Just whacking some magnifiers in front of a panel and calling it good will “work” to some degree, but devil is in the details if you want good performance. The entire point of a HMD is to produce stimulation of your visual system that is as close as possible to the natural light field you experience viewing the real world. At practical consumer cost points and with the technology available right now the lens is near-optimal for the panel and the objective function it was designed for.

Why do you think almost every high-end HMD since our Steam Sight prototypes were demoed uses a frensel based lens design?

Now I don’t for a moment suggest there aren’t better optical designs possible. We already have better ones, no doubt others working the HMD space have also caught up and likely have their own high performance designs for next generation HMDs too. I also recognise that some people care about different aspects of lens performance than others. But if you are wanting a “better” lens for your current HMD just realise there is a lot to try to optimise for at once and there is a great deal of prior art to understand before you can truly design something objectively better.”

That’s not how it works legally (thank god), it’s like software update: if you stop being subscribed you just don’t get newer update but can of course continue using your current one