VR optics and why inter-pupillary distance (IPD) means too many things | Hacker News Reader

VR optics and why inter-pupillary distance (IPD) means too many things

tomforsyth1000.github.io

65 pointswalterbell25 comments

> It's actually astonishing how often developers accidentally switch left and right eyes in code – effectively having the ICD be negative rather than positive – and it takes ages to consciously notice, if ever. But your subconscious notices, and you will end up being sick, and you won't know why!

This is the most amazing anecdote in the article to me. Is the brain able to use this reversed-perspective data to determine distance and scale, or does it give up and pick a single eye? Is it like those glasses that flip your vision upside down, in that you'll get used to it after a week, and have to readjust to the way things normally are afterwards?

I think it might be a bit like the hollow face illusion:

https://en.wikipedia.org/wiki/Hollow-Face_illusion

When I was playing an early version of HL2 VR if you walk right up to the wall, the crowbar you are holding goes through it but the wall stays at the same distance. A very weird feeling.

The effect of swapped cameras is sort of 3d-ish, but doesn't look quite right. When you switch it to correct it pretty much instantly looks way better.

Is it like how a Magic Eye picture looks when you cross your eyes to "match" the sides rather than relax and focus in the distance?

Yes, exactly analogous!

The Valve Index has an IPD adjustment slider on the bottom. I can tell that it does...something...but, with very wide margins, I can't tell what the right setting actually is for my eyes. Anything +/- a hell of a lot all just looks fine. So maybe it doesn't actually matter that much.

It changes how nice the depth perceptions works, reduces nausea if set properly.

Similar for me with an Oculus Quest. Maybe if I left the adjustment at one or the other extreme for an extended session, I'd notice something, but for my usual 30 minutes or so, I haven't seen any difference between settings.

I've found it affects how sharp lines look for me on Quest. I like to find a vertical line somewhere and dial in until it looks decently sharp.

Try sideloading QuestIPD [0]. It shows a test pattern that's supposed to help set the slider properly, and it shows you the exact setting value you're using.

[0] https://sidequestvr.com/#/app/303

The latest software update for the Oculus Quest shows you what you’re setting the slider too now as well, FWIW.

when your ipd is off its roughly the same thing as being slightly cross-eyed or slightly wall-eyed. if its small enough and the game is low-res enough it can not matter, but if you feel "eye strain" or a sortof between-the-eyes headache after playing for 20 minutes thats where it comes from. its subtle so it really gets you over time, not at any one moment.

here's a good howto on measuring your ipd to get it right: http://doc-ok.org/?p=898

Speaking of the index, try enabling the camera passthrough to experience severely mismatched IPD and camera spacing. I imagine this is what it feels like if ipd is set too high, but cant say because i leave it set at maximum.

https://www.reddit.com/r/ValveIndex/comments/eauwzk/i_change... If you have it set to maximum and still feel weird the link above helped some people.

In this article's terminology, I think that slider controls "IAD", and the reason why it doesn't change much is explained under the subheading "Collimated images"

> In this article's terminology, I think that slider controls "IAD"

Of course it does; obviously the slider doesn't move your pupils. But it's meant to compensate for your personal average IPD. I think you're right that the collimated images section probably explains the result, though.

The Index also has relief adjustment, which is high on his wish list at the end of the article.

As a pathologist, I spend a fair chunk of every day using microscopy optics which are in every way equivalent to AR's IPD problem. The honest answer is your brain has to learn to integrate those two images, and it will take months of daily use for multiple hours, with associated headaches, neck aches, back pain, etc to figure it out exactly right, but the trick is that by then, you won't have figured it out exactly right. By the time everything snaps into place, you brain will have also learned to snap it into place. My eye-brain system gathers information through oculars in a way that others do not. It's a matter of physical training, like so many things.

That's not to say quality doesn't matter. My undergrad is in physics, and the quality of the oculars in a clinical microscope puts to shame pretty much everything else I've seen. Even telescopes at the tops of mountains aren't as nice, ergonomically.

Somewhat related - I made the mistake of putting effort into learning how to stereo free-view Google Cardboard / Daydream VR apps. At the time it was kind of interesting what it felt like.

Except I must have made something super-sensitive in my visual system, to the point where now it’s almost TOO easy to stereo-fuse repeated patterns — though having said that, my visual system is kind of different I think anyway. Now if I see repeated patterns I’ll start getting phantom stereo fusion if I keep my eyes looking at one spot and relaxed too long. It’s not distressing or anything, it’s just really unusual.

The article was interesting an informative, but it's really surprising to me that all humans have the same sized eyeballs. I would never have guessed that!

Interesting... birthworks.org: "From outward appearances, by three months, our eyes are the same size that they will ever be as the corneas have reached their full width"

What I'm most curious about is what mechanisms control that, given the most obvious one to me---shining light through the developing lens and determining if the retina is getting good image resolution---is obviously impossible inside a body.

The actual mechanism might be something like that!

Nearsightedness is often caused by the eyeball developing to be too long. It’s actually dramatically increased in some places in Asia, where 90% of schoolkids can be nearsighted. [1]

There’s a lot of research pointing towards biological processes involving contrast (which is probably a decent proxy for focus) being involved in eye development, with maybe different visual stimuli (due to more time spent indoors) being a potential cause of the increased myopia rates because it doesn’t activate the specific mechanism in the right way. [2] [3]

[1] http://healthland.time.com/2012/05/07/why-up-to-90-of-asian-...

[2] https://www.sciencedirect.com/science/article/pii/S004269891...

[3] https://www.nature.com/articles/s41598-018-28904-x

Does shortsightedness and astigmatism matter much for VR or are the hardware lenses so strong that your eye incorrectness becomes just rounding error?

I have horrible far vision and can't see without my glasses in VR. I also have a very pesky lazy eye and need a prism in my glasses lenses.

Whatever your eyes have you will bring with you in VR pretty much.

Reply on news.ycombinator.com