How To Look At Stereoscopic Image-Pairs

Very easy. Look at them cross-eyed.
It's that simple!

You can indeed perceive perfect 3D-images without any technical help by looking at stereoscopic image pairs cross-eyed.

I am not talking about those "Magic Eye™" 3D-images consisting of pseudo random dots (also referred to as "S.I.R.D.S."=Single Image Random Dot Stereograms). These pictures have to be looked at by staring through them, almost as if you where looking at a point in an infinite distance.

I am talking about simple pairs of pictures like they have been taken since the very beginning of photography using 2 cameras with a little distance between them.

Both variants of 3D-viewing do not need any technical aids like special glasses or other devices.

Instead they both depend on decoupling to focus at a certain distance on the one hand, and converging to quite another distance - something which is never used in everyday natural eyesight.

The magic eye method means setting the crosspoint near infinity, while the focus has to be on the paper at some 30, 40, 50 cm or whatever.

Cross-viewing on the other hand needs the crosspoint nearer than the paper (or screen) is, which for that reason is best kept at least 1 m away, so that you don't need to force yourself to cross-eye to the very extreme, which would be rather uncomfortable.

And whilst S.I.R.D.S. usually "hide" a picture within the picture, having nothing to do with one another, stereoscopic picture pairs hold nothing but their true 3D structure, as far as that is contained in the 2 perspectives shown.

 

 

To get the pictures in 3D, look at them cross-eyed in a way that you see 3 pictures of the same size instead of the 2 ones really shown. The central image may be blurred first, which doesn't matter for a start. But try to get it stable, keeping the same size as the marginal pictures. It is sometimes "trying to escape" somehow; don't let it - keep it!
In case you see 4 pictures, you squint way too much.

In case of the 3D test-image above you should see a cross within a circle underneath different coloured numbers. The green number must not be the most distant one. If it is, you have wrongly applied the S.I.R.D.S. method.

At some point it will become clearer and clearer and there it is! You have managed 3D-viewing without any stupid goggles or the like!

The impression is really worth the effort, so don't give up so easily. Children often manage it in little more than seconds, after they have been told what to do exactly.

But why not showing the 2 images uncrossed? Well, that is possible, but it has a serious disadvantage: the single image must then always be kept smaller than the distance of your eyes. That is because you cannot split your viewpoints apart. On the other hand you can print (or show otherwise) crossed stereoscopic image-pairs as large as you wish. Simply step back until you can cross-focus them easily.