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Comment by eastbound | Hacker News Reader

Why can we have 2-lense glasses that move the focus to infinity?

ELI5: In opticals, “rays” coming from a near object (=mobile phone) are angled, while rays coming from afar (=end of a landscape) are parallel. The job of pupils is to bend the rays from the focal point ahead to the focal point on the receptors in the eye. The eye is a rest when looking afar, because rays come parallel, and thus there isn’t much to do. The eye is strained when trying to focus one something closer.

I’ve always wondered why we all had that UV filter on screens and never took care of making the rays from the computer screen parallel, using a lense.

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You and I and a few others around the web all have had this idea of making screens look farther away, by changing focus with positive lenses and and binocular convergence using prisms. I actually wrote this comment with the math for determining the required prescription (since you can simply order them online) just a month ago.[1] I then found that the concept isn't uncommon when I discovered an older comment with the same idea, which I've misplaced, but a search turns up another thread revealing that this already exists as a product marketed for gaming.[2]

[1] https://news.ycombinator.com/item?id=31349629

[2] https://news.ycombinator.com/item?id=21742229

You might enjoy checking out https://endmyopia.org/

There's calculators on his site also for astigmatism. I think also a list of optometrists who will understand if you want weaker lenses.

Good info on refractive error there, though I don't see much on prism lenses used for this purpose. While searching, I did discover this book, the Myopia Manual, which they're hosting a copy of. It looks quite thorough and does have a chapter on using prisms to match vergence with accommodation in plus lenses. The book also has its own site http://www.myopia-manual.de/

I also found an older myopia submission where a comment links several related sites.[1] frauenfeldclinic.com now redirects to endmyopia.org; archive.org confirms that the old domain was the same site, but oddly the new domain has an exclusion applied. As one reply noted, myopia.org really is an excellent display of the Time Cube design language.[2]

[1] https://news.ycombinator.com/item?id=9230093

[2] http://www.myopia.org/conspirators.htm

There's people in the endmyopia forum using base in prism with their plus lenses - look for espantoso and nycmao :)

Personally, I just use plus lenses without prism.

Around 1995 I wrote a DirectDraw text-editor that would render two images and force you to defocus your eyes like the op-art-3d puzzles: making the viewer have to focus far away. It worked for images but not for reading small text.

You can do that cheaply by picking up a pair of reading glasses, or glasses with lower power if you are already nearsighted. Roughly, infinity will be at 1/diopters in meters, so +0.5 glasses will make 2m away at infinity, +1.0 at 1m, and so on, and similarly if you are at -3, -2.5 will make 2m infinity, etc. It's not exact because they are not thin lenses and there is a separation between lens and eye, but it should be pretty close.

I've been using one less diopter correction for a while most of the time, with an additional pair of glasses with the full prescription for driving. Not sure if it does anything or my nearsightedness just naturally stopped progressing though, but since it's working and not bothering me I have no interest in finding out.

How would it work? Where would you put the two lenses? Consider:

- You can't really have two lenses cemented together. That'll correct for chromatic aberration but, other than that, the lenses would behave as one (except for deviations from thin lens approx.)

- You can't have glasses mounting two lenses "d" apart for two reasons. 1) Having parallel lenses would terribly uncomfortable, heavy, and awkward 2) More importantly your eye and the two lenses would never be aligned (as soon as you move your focus away from the one spot the glasses were aligned for, the optical system performance would collapse)

- The best you could do, then, is contact lenses + eyeglasses. But then you have all the bother of wearing glasses and eyeglasses. Also, it's not obvious to me it would work since the contact lenses are in contact with your cornea, the pair behaving like a single lens.

I think GP is mistaken about two physical lenses being needed (until it's the future and we're all wearing expensive smart glasses, in which case you do want an additional interchangeable lens for this purpose). When designing the system, it can be thought of as a lens that corrects for refractive error of the relaxed eye (moving the eye's far point to infinity) stacked on top of another lens that makes light coming from an object parallel (producing an image of the object at infinity for the first lens and eye to receive); to implement it, you only need one lens with the combined power of the two.

Edit: GP might also be talking about eyeglasses with adjustable focus, which apparently are already available. https://en.wikipedia.org/wiki/Adjustable-focus_eyeglasses

I think you get the effect you desire by wearing glasses with + when in front of a computer. anecdote: i started with -0.5 (10-15 years ago), per ophthalmologist "advice" wore glasses all the time (including computer), got to -1.75. then one summer spent some time without any glasses (just because i wanted to use the sunglasses) and at the end of the summer the vision went back to -1.50. This got me thinking that wearing glasses all the time is not that good. 4 months ago started to experiment, no glasses all the time and +0.5 when in front of the computer. Started with -1.25, and now I am at -0.50/-0.75 ... take it as you want.

Assuming that it’s technically practical, the results would be very unsettling: the phone screen would look like a window with the content “behind “ the window, very far away.

I doubt that effect would be very strong as the effect of a magic eye massively dominates any feeling we have to notice that our eyes aren't having to do as much of whatever you'd call this lensing work.

…But geometric aberrations might be annoying: The image is perfect in the center but blurry/rainbowed 10° from the center, etc.

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