Is diverging harder? I find it easier. Maybe it is from long ago practice on stereograms, but I'm curious if it could be due to neurological/physiological differences.
Crossing is easier because you can simply hold your finger in front of your eyes and look at that for practice.
Diverging requires you to look past the image, meaning you have nothing to really look at, which makes it difficult to figure out what your eyes are even supposed to do.
Those stereograms aren't helping much either, since they look like nothing until you get it right. With cross-eye you have instant double-vision that you just need to align.
Cross-eye also works across much larger distances, diverging fails when the images are too far apart.
It depends on the image. If the two images are too far apart then it could require your eyes to diverge, and not to just converge slightly less. That might be impossible.
Diverging is way way easier for me, but I am positive that's because of the 10's of hours (at least) that I spent staring at magic eye images as a child.
My whole life I've been doing stereograms by diverging, but I couldn't get the three images in the post (the pairs would get closer but never fully overlap), so I tried crossing based on your comment. It was way easier than diverging (obviously, since I couldn't do it otherwise), but it took me a few tries, because I think it's actually /too/ easy to cross your eyes compared to diverging - I was way overshooting when I crossed my eyes. The trick was to notice this, and then control the un-crossing until they lined up.
Diverging is definitely harder, and might be out of focus. To keep in focus I found it easier to focus on the right image and then cross my eyes, rather than staring in the center and then staring through the screen into the distance while trying to make them line up.
I used to not be able to do the "magic eye" 3d images until recently, and this trick is pretty handy.
For crossing just focus on your finger and then remove it.
Looking far away may be harder, and afaik it’s near impossible to look “past infinity”, iow pictures must be less wide than the distance between your eyes.
Btw these two methods aren’t equivalent in watching stereograms. If you look at one and see something but it doesn’t really make sense, then it’s probably the opposite chirality.
Personally I hate the crossing method because it makes your eyes feel strange for a while.
how I approached crossing: first practice just crossing your eyes and observing how every object has two images in this case and when you slowly “uncross”, they merge back into one. you can use anything in your surroundings.
then for the stereogram you do the same, observe the out of focus edges of the left and right pictures, then slowly uncross until left and right image occupy the same spot as though they were the same object. now its out of focus, but one (ok, actually three, because there were two, you “doubled” that by crossing, then merged two of them. but ignore the other two and focus on the merged pair)
sometimes you will merge images of the same picture, in this case you are just back at your normal vision, repeat :)
then you try to keep them overlapped and focus the vision, try to “believe” that you are really looking at a single object.
