undefined | Better HN

0 pointsMarkusWandel1y ago0 comments

Wait, that's not crossing your eyes, it's uncrossing them. Ordinarily if you look at something nearby, your eyes aim at a common spot. But when viewing a stereogram, you need to convince your eyes to aim at a spot more distant than the subject.

This is easy with practice, however IMHO it helps to be significantly nearsighted. Then you simply take off your glasses, and can look at something nearby with infinity focus, which is naturally associated with uncrossed eyes.

I don't know whether it's possible to train yourself to diverge your gaze, i.e. stereoscopically see images that are separated more than your pupil distance. Certainly I can't do that.

0 comments

phailhaus1y ago

For spot-the-difference, crossing your eyes is more effective and easier to "dial in" than uncrossing them. You're essentially making each eye look at the opposite image. If you try uncrossing, then you need to make sure the images are at the exact correct distance to cause them to overlap with that technique, because you can only uncross your eyes enough to look straight ahead.

nemetroid1y ago

Looking uncrossed at the images in the article on my phone, I can easily achieve the effect uninterrupted between fully stretched arms and about half that.

phailhaus1y ago

Sure, but that's the limit. I didn't say it was impossible, just that crossing your eyes basically works all the way up to your nose.

seeekr1y ago

Is that true? It seems that our eyes are mechanically capable of looking in divergent directions, what's the reason that we're not able to "uncross" them beyond looking straight ahead? (Edit: Anecdotally I can confirm for myself that I'm not able to do it, so wondering if there's anyone that can.)

thfuran1y ago

From a control system standpoint, if you have one control that rotates both eyes the same number of degrees left or right to determine gaze direction and another to rotate both eyes the same (positive) number of degrees inward to control fixation distance, you can't specify the left eye rotated left of center and the right eye right, even if each eye physically can rotate that way. Not sure if that's how eyes actually work though.

ses19841y ago

It’s a good thing that properly designed stereograms take this into account and don’t require you to uncross your eyes past that point.

phailhaus1y ago

That's because you have to find the distance between your eyes and the stereogram to make it work. Crossing your eyes is easier because your eyes can turn inwards far more than they can turn outwards, so it works at more distances.

satvikpendem1y ago

See my other comment about cross view vs parallel view, looks like you can do one vs the other and the author can do the opposite.

vault1y ago

Wow. Thanks to MarkusWandel I discovered I can focus images while crossing my eyes and finally understood your comment. I've always done the "uncrossing" since I was a kid.

semireg1y ago

While intuitive, I’m not so sure. I look at the center line and slowly cross my eyes until the 3rd image slides into place and then I get focus lock. At no time do I feel my eyes uncross and go the other way. Hmm!

teddyh1y ago

Both work equally well if you just want to spot differences. Cross-eyed view is somewhat easier to do, since people naturally cross their eyes when looking at something close to their face, but there is no natural reason for one’s eyes to diverge. But cross-eyed view also gives a subjectively smaller image, and is also not the usual way autostereograms are made to be seen.

jodrellblank1y ago

> but there is no natural reason for one’s eyes to diverge.

When you’ve finished looking at something close to your face and your eyes need to uncross. So you do that eye movement while still holding the image close to your face. Note you are looking “past” where the image is. As long as the image is closer than your infinity focal view you can do this, it doesn’t have to be close to your face necessarily, Magic Eye posters on walls do work.

j / k navigate · click thread line to collapse

0 comments

phailhaus1y ago

nemetroid1y ago

Looking uncrossed at the images in the article on my phone, I can easily achieve the effect uninterrupted between fully stretched arms and about half that.

phailhaus1y ago

Sure, but that's the limit. I didn't say it was impossible, just that crossing your eyes basically works all the way up to your nose.

seeekr1y ago

thfuran1y ago

ses19841y ago

It’s a good thing that properly designed stereograms take this into account and don’t require you to uncross your eyes past that point.

phailhaus1y ago

satvikpendem1y ago

See my other comment about cross view vs parallel view, looks like you can do one vs the other and the author can do the opposite.

vault1y ago

Wow. Thanks to MarkusWandel I discovered I can focus images while crossing my eyes and finally understood your comment. I've always done the "uncrossing" since I was a kid.

semireg1y ago

teddyh1y ago

jodrellblank1y ago

> but there is no natural reason for one’s eyes to diverge.

j / k navigate · click thread line to collapse