Tech Talk #14 : Pancake Lens

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The Fresnel optics features a wide field of view compared to Pancake but is prone to chromatic aberrations (ghosting/overlapping colours). Furthermore, software calibration taking up processing power must account for Fresnel lens known as “distortion’.

Pancake, on the other hand, works by folding a series of lenses into a curved shape and bouncing light within the glass or plastic. This allows VR HMDs to be thinner and lighter, while also freeing up processing power due to the lack of distortion.

The Pancake lens design will bring on stylish design that attract a wider audience?

Compared to Fresnel lens, what’s the downside from Pancake optics?

What does it signal for the future of VR HMDs?

Kopin announced an all plastic Pancake lens design called P95, which specially optimized for use with 2.6K x 2.6K OLED high-brightness microdisplays.

Like augmented reality, VR is on a path to a slimmer and lighter future.

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Is the pancake lens approach inherently incapable of or disadvantaged for wide FOV? Or is it merely that early incarnations of them have relatively narrow FOV?

Another thing I wonder about pancake lenses. If they have poor light transmittance, does that mean they heat up? The energy from the lost light has to be going somewhere. But maybe it’s not enough energy in total to matter.

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Stems from Pancake’s boucing of light within lens itself, resulting in low light efficiency.
Problem of ghosting and is also a scourage for this lens.
Also,the cost of Pancake is nearly 10 times higher than that of Fresnel lens

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Kopin says P95 has a field of view 95° diagonal – around 20% narrower than typical consumer VR today. :pleading_face:

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As of right now, I think Pancake lenses will be great and what is truly needed for something like working in VR to become viable. It makes headsets thin and light enough to be both extremely comfortable to slip on and wear for hours without the slightest strain. I’ve seen some express wanting to have a ‘monitor replacement’ VR headset, and I’ve never felt like it’s viable long term even with the super high clarity HMDs. The comfort just isn’t there yet.

However, I am not personally in love with the current state for gaming given how it feels like FoV is even more limited with pancake lenses than with current HMDs. The industry is regressing on FoV and that frustrates me. Would I give up some FoV to have pancake optics and the extra comfort? Perhaps. I might even be able to live with something like 130 horizontal in a form factor like the Arpara or the MeganeX if the rest of the features were compelling and good.

But, until we can reach a good point like that, I don’t have any interest in pancake lenses. I’ll happily take bulky HMDs, such as the current Pimax designs, if it means being able to have very wide FoV and a packed feature set. It’s sort of like laptops in a way, where sure very small form factors that’re easier to transport exist, but by the sheer nature of having more space a 17-inch laptop can usually fit far more into it, be it things like ports, unsoldered ram, higher power components due to better cooling, vs a 15.6 and especially 14-inch laptop.

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Hum, let’s dream, what about a mix of both : a lens composed by a pancake for the center, mounted on a fresnel lens to cover the peripherical area of a wide fov ?
:slight_smile:

So exactly what Pimax are claiming for the 12K?

12k will have “Bionic” lenses, so aspheric directly forward, then fresnel towards the edges. The processor on the HMD works with the Tobii eye tracking to correct distortion. It won’t be using Pancake lenses, this is just a discussion about tech that’s out in the world.

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I stand corrected then, thanks.

It’s the Crystal that is meant to be released with pancake lenses, isn’t it?

I don’t believe Pimax is shipping any pancake lens headsets. I’m actually not sure what they are using for lenses on the Crystal, but I’m quite sure its not a pancake lens design.

The Crystal uses glass aspheric lenses.

The biggest benefit of pancake lenses is comfort. To be totally honest, the 12K looks perfect in everyway except this one point. The current fresnel form factor is going to look like like those giant cellphones from the early 90s.

I guess one thing that might slightly reduce the comfort gain, is that the screens need to be brighter, in order to compensate for the loss in the lens train, which strikes me as likely to mean more heat, closer to the face… :7

I was thinking it was likely an aspheric lens, but I wasn’t sure – thanks!

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Mate Pancake( Cambria/ Pro)
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Arpara Pancake
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Yvr Pancake:
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Sorry to put in a point that’s not really related to Pancake Lens, but just the lens.
Most headsets today are designed for the 20/20 vision people, which I found really strange. How many people here actually have 20/20 vision? Why headsets are not more accommodating for near or far-sighted people?
You know, there will be way way more distortion and ghosting if I have to put my glasses on top of the lens, and the glasses will make the VR experience much worse.
In the early days of VR, some headset’s lens actually can be adjusted forward and backward, which helps my near-sighted problem, but today after trying Pimax, HP G2, and Meta Quest 2, I’d say the most concerning issue for me is “can I see clearly without eyeglasses in my headset”? Pancake, aspheric or Fresnel makes no difference when I have to wear the glasses within the headset. It will be bad anyway.
For some reason, when wearing my Pimax 5K Super, I can see things comparably clearly without my glasses, and that’s a huge plus for me. And this is why Pimax headset is my favorite: I can see super-wide pictures with my bare eyes ! The screen-door effect is just a tiny problem.
So I sincerely hope the upcoming Crystal or 12k allows me to keep seeing things this way. I also wish there is some way that they can adjust lens focus for people not having 20/20 vision. For me, a thinner face pad already did the trick.

Pimax has said the Crystal and 12K will have diopter adjustment.

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Well, maybe not quite entirely specifically unrelated, given one of the noteable features of recent headsets with pancake optics, such as the Arpara, has indeed been diopter adjustability. Don’t know whether you had noticed this, and this is what prompted your post, or not… :7

I have kind of been waiting for reports of some home tinkerer having motorized that dial in one of those HMDs, to produce a sort of makeshift varifocal functionality. :9
(No idea how much the zoom level changes with this change in a pancake setup, either…)

Crystal specs do claim a 7 diopter adjustment range; I don’t recall anything about whether this range starts in the negatives, or if that is only plus 0-7… I wondered a bit whether the diagonal flange on the eyetubes, in the parts pictures that were posted the other day, were part of the adjustment mechanism in any way, but who knows – the tubes themselves look to be completely rigid…

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If that´s really true, I will for sure buy the 12K. I found little amount of other headset with such diopter adjustment. to mention VIVE Flow (forget about FoV). I just quote from a reddit post and adapt a little bit " 75% of adults use vision correction. Even the CHEAPEST binoculars have diopter adjustments…"
Which means, those who can afford (Hear me, PIMAX, Your dear customer is speaking!), often require diopter adjustment + IPD adjustment or at least fitting for wearing Glasses or diopter adapters.

So, Pancake or Fresnel? In the end it will be hybrid lenses to have advantage of both, I bet on.

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