Hybrid Lenses? Teach me

Just thought I’d stoke a technical conversation about “Bionic” lenses in the proposed 12K.

What I understand is:
Aspherical lenses produce less god rays.
Fresnel lenses produce less distortion.

Pimax proposes hybrid “bionic” lenses that claim to take the best of both worlds.

I worry that you would necessarily have some kind of transition across the hybrid portion causing a distortion of its own.

I also have trouble understanding the difference between distortion and chromatic aberration.

The sweet spot on the 8kx is huge, while the “smearing” on the outer edges is totally acceptable to me as I feel like unless I’m trying to read something there its not a problem.
Is the smearing distortion or abberration?

I also see godrays with anything bright in the center and not on the periphery (planets, white text) but its only somewhat annoying.

Thoughts? Don’t be afraid to get technical I love that. I’ve read wikis on each and listened and watched the 12k introduction (this time, haha)

Are there other properties? Other concerns?

First of all, a bit of a long standing pet peeve – not something about you; It’s over the place: The use of “aspherical” as were it the opposite of “fresnel” – You can take a spherical profile conventional lens and “collapse” it down to a fresnel format, and you can take an aspherical profile conventional lens and collapse it down to a fresnel format.

You already have a transition zone with the current 8k/5k series lenses, where the aspherical… hmm: “S-ramp” starts the conventional lens profile on the “user side”, from being plain flat in the periphery, producing the characteristic “fried egg” profile.

I am happy for you, that these lenses work well for you - others find that transition zone very disturbing; A ring of blur, distortion, and increased surface reflections (funnily enough, the last due to the “fresnel” effect (light bounces easier off a surface when striking it at an angle, than when hitting it straight-on)).

The new lenses in the 12k “Vision” series will ostensibly add to this the phasing out of the fresnel lens part on the flip side of the lens element that has this “egg yolk” aspherical lens, where the two meet up. How well this works, we who have no privileged connection to Pimax are yet to see.

Chromatic abberation is caused by different wavelenghts of light refracting by different amounts, when they transition from one material into another, which is why you can produce a colour spectrum by shining a ray of white light through a prism, and why you can see a white line gaining a red and a blue fringe on its radially opposite sides, were you to turn off the software chromatic abberation compensation, or just look through the lens off-centre.

This distortion is essentially the same thing as the overall distortion, if there had been no CA – it just happens to apply with different strength for different primary colours, and so it does in the counteracting barrel distortion that is done in software before the eye textures go to the screens: Red, green, and blue are distorted by separate amounts, as much as is needed for each colour, to cancel out the opposite direction distortion caused by the lens.


Excellent. Love it. After your message I looked through the Pimax 8KX I don’t see much pure chromatic aberration (on stars for example at the edges) - the light doesn’t split into the spectrum, but that’s probably because of the distortion smearing that occurs at those angles anyway, which is very evident at the top, bottom, of course very drastic at the high FOV areas left and right. CA was much more noticeable in the G2. In fact all the edges have the CA unless I got into the smallest sweet spot; at which point it was at all the edges at once. The 12K seems to promise nearly edge-to-edge clarity and will only believe that when I see it. I guess I just want to know

Here is what the 8kX looks like without lenses – that is quite a bit of chromatic abberration compensation, and it works remarkably well. :slight_smile:

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So they compensate for CA already? Through software? Holy crap! Thats REALLY bad. Incredible they can compensate at all!?

Dumb followup question - why cant they correct for distortions…or do they? And if they do why is there so much smearing in the periphery of the FOV -cant they just fix that? Or is that something beyond distortion…

They will have to use a mean setting for all possible eye positions because distortion is different when you move your eyes

This is another reason why eye tracking is important. Because theoretically it could dynamically adjust the distortion profile since it does know the positions of your eyes.

I don’t think there are any VR headsets that currently do this though. So there’s some question how well it would actually work in practice.

Man I hope to live long enough to see all this come to fruition.

Not a lot of headsets would need something like that either

Were the 8kx lenses hybrid?

No. The 8KX uses Fresnel lenses.

Really depends on what you mean by hybrid.

The Oculus Rift, and HTC Vive had hybrid lenses (although only one of them made a big deal out of this); They were fresnel on one side, and conventional aspheric convex on the other, and I suspect the same goes for subsequent devices from both (and other) makers. The same goes for the famous “fried egg” lens in every Pimax 8k/5k series HMD - fresnel toward the screen - conventional toward the eye.

The difference with the new lenses, for upcoming devices, seems to be twofold (…from concept renders; Unfortunately it was hard to tell anything from when Kevin held his unit up in the general direction of the camera, the other day (EDIT: Too much reflecting)): 1) They look to be a stack of two lens elements, like the Valve Index, and 2) The backside of the nearest-to-the-eye of these does not have the fresnel zone, at least in the in the middle. Whether the backside of this fist element is plane, or has a bulge on that side too, is hard to tell, assuming one can go by the pictures in the first place.
The second element, however, still looks to be fresnel all the way to the centre.

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Yeah I’m still not clear> The 8KX is advertised as just fresnel, but had a very nice sweet spot and looks like a fried egg pattern to me as it’s very smooth in the middle of each very large lens, with the lighthouse pattern on the sides only - but then, when Kevin discussed the 12K he described it as having the distortions but so far out in the FOV that it didn’t matter and he didn’t say it was aspheric per se - the video feed got garbled and he bounced back and forth with Sebastien as a result trying not to step on each others speech…

I honestly felt like the 8KX had that “hybrid” design already since honestly I didn’t think it is all that bad in the central … 90 degrees of FOV.
I guess I was just trying to understand what’s in the 12K more and how it differs from what the 8KX has.

BIG shame Kevin couldn’t do squat with the lenses, couldn’t turn it on, couldn’t do anything related to the display. I felt like that left me getting about 10% of what I wanted from his interview. Was glad to hear from Pimax and that they’re on track…but I didn’t gain anything from his interview other than reassurance.

EDIT I think my fault is not understanding the difference between aspheric and conventional and convex… I think I’m getting those terms and definitions mixed up…wikipedia is over my head hahah

It is harder to change already formed opinions than create new ones.

There is a general and popular misunderstanding about the nomenclature of the lenses in VR headset, or lenses in general.

The lenses, in general, are described by the shape of the curved surfaces they are formed from:

  • Spherical - the surface is a part of a sphere,
  • Aspherical - the surface is more complex.
    Both of those types are usually considered to be symmetrical, in a sense that the shape is some kind of a rotational shape, or in other words, the shape is symmetrical along its optical axis.

More generic form (i.e. asymmetrical) is then anything else, with its most complex variant known as free form shape, which is usually a custom design for particular application. You may know those type of lenses from prescription glasses, where they are referred sometimes as “digitally surfaced”.

The difference between different categories is usually defined by the mathematical complexity of the defining formula. The “basic” aspherical (and even asymmetrical) lenses are defined by relatively simple formulas, while the true “free form” lenses are basically spline meshes.

So far I have not mentioned Fresnel lenses, because Fresnel principle is just a way of realization (or implementation) of the aforementioned types in a different way. It is a (very smart) way to compress otherwise thick body of the conventional design, while maintaining the same optical property. Well, not exactly the same as VR users are already aware of god rays, stray light, loss of acuity, etc., but in general they are just an equivalent of the corresponding traditional design with certain advantages and trade-offs.

So, if you would want to classify the lenses in some headsets correctly, you would say, for example for:
OG Vive - it has symmetrical, most likely aspherical, Fresnel lenses
Varjo - has probably the same, but conventional (non-Fresnel).

Pimax has most likely asymmetrical (which implies aspherical as well) Fresnels.

The final part is what is then considered to be a hybrid design? This is when two (or more) different implementations are used in one piece. E.g. you have one part of the lens of the Fresnel type (typically the center) and other other one (typically the outer rim) of the conventional design.

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So the 12k is a mix of both…Kevin said theres no apparent transition. I was hoping that it would lighten the hmd. Turns out the removal of the heatsinks (replaced with fans) may lighten it more than lens design. Excitingly he said that yes there is fresnel but they are so far out that it doesnt impact much. Cant wait!

I’m really hoping it gets lightened quite significantly or it’s a no go for me. 8KX is just too heavy for me I’ve come to learn.

Yeah I put pulleys on the front for seated games

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