Your camera has the ability to take three dimensional photos. Your screen has the ability to display three dimensional photos. You’ve probably never used either. This isn’t a hidden feature of some new phone hardware release, it’s a feature of your brain. All your brain needs to see in 3D is two pictures, and you can trick your brain into seeing 3D on a flat screen using just your eye muscles. I will teach you how. I’ll also tell you why you should.
Binocular Vision, and Faking It
Around a third of your brain is devoted to vision, and accordingly, it is amazing at it. From just the two small 2D images that are sent to your brain from the backs of your eyeballs, your brain reconstructs the entire 3D scene that you experience when you look around. Because your eyes are a few inches apart, they see two different views of the same scene, and those two views are all your brain needs. Distance causes objects to shift relative to each other when you see them from different angles. You can see this most clearly by moving your head from side to side and watching how things move. Your brain uses that discrepancy between the two views of your two eyes to reconstruct depth.
Because your brain has this power, all you need to do to see an image in 3D is to send different images to each eye. It doesn’t matter how you do it. Every 3D display technology works this way, the only difference between them is how they get each image to only one eye.
Red/Blue 3D glasses filter out images that have the same color as the plastic lens. Modern 3D movies use polarizing filters, but the principle is the same. Two images are projected using orthogonal polarizations of light, and are filtered out by lenses in the glasses with the opposite polarization. Holograms show different images at different angles, and your eyes are at different angles. VR goggles put separate images on the screens in front of each eye that correspond to the views of two eye-spaced cameras in the virtual world.
Seeing Cross Views
If you don’t have any fancy technology, that doesn’t matter. You have eyes, a camera, eye muscles, and a brain, and it turns out that’s all you need.
If you have two images that show the views from two different positions, all you have to do to see the objects in 3D is to have one eye look at one image, and the other eye look at the other, and your brain will do the rest. You can do this either by crossing your eyes a little bit, or diverging your eyes a little bit. Most people have only ever deliberately controlled their eye muscles to cross their eyes, so find that to be easier. (It is also easier to focus on an object in front of the image than behind, because you can just put something in front of it and look at it.) Accordingly most stereograms are designed to look correct when you cross your eyes. To use the other method, the images have to be swapped or the 3D effect will be inverted.
Peephole Method
If you are doing this for the first time or aren’t comfortable crossing your eyes, then the easiest way to start is the peephole method. Hold your hand up with your fingers in a circle and look through the circle at the image. Position it so your left eye can see the right image through it, and your right eye can see the left image through it. Check each eye by closing the other until you see only one side in both, then open both eyes. If you focus on your hand, you should see the 3D image pop up inside of it as if you are holding it. It may appear blurry at first. Of all the methods, this one produces the least eye strain, and has proven to be the easiest for beginners. Positioning your hands this way tells your eyes exactly where to focus.
Cross-eyed Method
If you are comfortable crossing your eyes and feel like you have good control of how crossed they are, then this method is faster, and gives you a more complete view of the image. Just cross your eyes slowly, and stop when the images align. Doing it correctly feels like this: First the images split in two, and you’ll see flickering blurry copies of both images slightly offset from each other. Then as you cross your eyes more, eventually the two images in the middle will align. The center image will resolve into a clear 3D image, with two flickering copies of it next to them.
Anchor Method
If neither of those work, then the best way is to focus on something in front of the picture, and hope that the images align on top of each other as a side effect. You can do this by holding your finger substantially in front of the image, and focusing solely on the finger with your eyes, while turning your mind’s attention to the image behind it while keeping your eyes still. To find the right distance to put your finger, make the ratio of the distance to the image to the distance between images the same as the distance to your eye to the distance between your eyes. If the images are the same distance apart as your eyes, put your finger half way in between.
Making Cross Views
All you need is two pictures taken from two different positions shifted horizontally. The easiest way to do this is to take a picture, take a small step to the left or right, and take another picture. If the object is close, you only need to move the camera a few inches. If the object is far away you may need to take a full step to the side. How far you step will determine how strong the depth effect is, which is ultimately a matter of taste. A stronger depth effect makes the result more dramatic, but makes the image harder to resolve when you cross your eyes.
To turn the image into a cross view, you just need to put the images next to each other. Any way you do this is fine, even just looking at the two pictures next to each other in your camera roll. If the 3D effect looks backwards, just swap the images. There is free software that can do a better job by aligning the images automatically, adding borders, and allowing easy adjustments, Stereo Photo Maker for Windows or OSX, Cross Cam for Android.
Why bother? Isn’t 3D just a gimmick?
3D has mostly been a gimmick. 3D movies use the depth effect mainly to throw things at you and make you flinch, not to add to the art. But every sense we have should have art in it, and our depth perception has been shortchanged. Depth is such an immature medium that we haven’t gotten past the kind of whiz bang novelty of The Arrival of the Train. (Notable exceptions to this are Avatar and Half Life: Alyx, which are enormously enhanced by being in 3D.) It is a huge part of how we experience the world, we shouldn’t give up on it.
There are some things that just can’t look the same without depth. To photograph a forest, and convey anything like the experience of being there, you need the world to give you other visual cues to add depth to the image, like fog. The world usually doesn’t do this, and as a result nearly every photograph of a forest looks like a flat disorganized mess. Add depth, and suddenly all the complexity and beauty reappears. You can show people what a forest is for the first time.
To photograph a cave, and convey the layers and scale of the rock, you need clever lighting, and even then it usually fails. The geometry of a cave is too unusual for cues like lighting and shadow to work reliably. The rocks are all the same color. Add depth, and there is no more ambiguity. The shapes take shape.
Depth literally adds another dimension to the composition. You’re no longer just positioning objects to lead the eye around the page, but also to lead the eye through space. What compositions could we create with this? Architecture or stage plays probably have more to tell us about this than visual art does. But it’s mostly still brand new and wide open. Go explore!
Gallery
Places for more images:
Parallel Views
If you are able to diverge your eyes instead of crossing them, then arranging the images the opposite way can give you a more relaxing and more natural stereo effect. This corresponds to focusing past the image instead of in front of it. There is an upper limit to how far you can physically diverge your eyes, they can’t go past infinity, so parallel view images need to be smaller to take up less of your viewing area.
For more images with this orientation, try the r/ParallelView subreddit.