Photography has an inherent limitation in that cameras typically capture images that don't have any true three dimensional depth. We have two eyes, but with the exception of specialised equipment, cameras only have one lens. There are ways to "cheat" however, and for almost as long as there have been cameras, there have been people trying to find ways to take and view 3D photos.
3D photography is experiencing a rush of interest and innovation, as more people experiment with better digital cameras, and a wave of new 3D movies, including the spectacular 3D epic by James Cameron, Avatar captivates audiences worldwide. 3D is the next big thing, and many want to create and see 3D photography, or stereophotography.
This article is not a history of stereophotography. The point is to teach you how to see 3D photos on the web. There are many different ways to see 3D, with just as many gadgets to help. The technique I will be showing you requires no special equipment. All you need to do is train your eyes to look at these images in what you might call an "unnatural" way.
WARNING: It's important to state right up front, that there is a small potential risk to your health with this 3D viewing technique. The risk is very small, but I must cover myself. If you have any known problems with your eye muscles, I recommend that you do not attempt this technique. If you experience any light-headedness, headaches or other symptoms, STOP IMMEDIATELY and rest your eyes. Everyone will likely experience some slight eye fatigue when learning this technique, so it is very important to rest your eyes regularly, and only look at 3D images for short periods of time. Even once you have perfected the technique, do not over-exert your eyes. You have been warned. If you attempt to learn this technique, you agree not to hold me responsible for any ill fortune that befalls you as a result.
Note: This technique will be impossible for some people. If you have poor eye control, a dramatic disparity in eye function or anything along those lines, you may not be able to see the 3D effect no matter how much you practice.
Now that we've cleared that up, lets learn how to see in 3D!
To see a 3D image, each eye needs to see a different view. There are ways to take photos like this, but I'll talk about that another time. When the two slightly different images are processed, they are placed side-by-side so that the viewer can use a special "crossed-eye" technique to overlap them, and see both views together in 3D.
Below is an animation that simulates what it looks like when you view these images in 3D. The instructions follow.
How to do it
Why crossed eyes? When overlapping stereo pairs without special glasses, you can get the 3D effect by crossing your eyes or diverging your eyes. I prefer the crossed eye method. I find it easier to control, and it is possible to view larger 3D images than with the diverging technique.
Sit square in front of your monitor, with the image directly in front of you, at about arm's length
Sitting further back makes it easier - you don't need to cross your eyes as much - but makes the image look smaller
Make sure you keep your head level horizontally, tilting your head will prevent you from merging the images
While keeping the stereo pair of images in the centre of your vision, slowly cross your eyes
The stereo pair will go out of focus and you will seem to see four images, as shown in the animation above
If you find it hard to cross your eyes, it can help to hold a pen in front of you and look at the tip with the stereo pair in the background
Gradually cross your eyes more and more - if using a pen to assist, start it close to the monitor and move it towards your nose
Continue crossing your eyes more, untill the centre two of the four images overlap and you see three blurry images, as in the animation above
Try and hold the centre image together - it is possible to "lock" it in place and see it as one image
The "locked" centre image should appear in 3D!
Now the tricky part, focus - while holding the 3D image in place, relax your eyes - drop the pen from your field of view if you are using it
If you can keep the 3D image locked and relax your eyes, it should eventually pop into focus, as in the last frame of the animation above
What you are doing here is causing your eyes to look at a space between you and the monitor, but focusing the lenses on the monitor. Our eyes never naturally need to do this, so it can be tricky to do at first.
Try and see the 3D effect yourself with the stereo pair below.
How did you go? If you were able to see the effect, congratulations! It really is very striking isn't it? If you couldn't manage to do it after trying for a while, leave it aside and try again tomorrow. It can be tricky to get the first time, but the majority of people can do it. If you find you are unable to see the 3D effect no matter how many times you try, then it may be that you are one of the few who for whatever reason will never be able to do it. I have no idea why, some people can't curl their tongues! *shrug*
Linking to this guide
If you take 3D photos yourself (I teach you how in this article), then please feel free to link to this article to give your viewers a clear, straightforward guide to seeing your 3D images. Just copy and paste the following code into the image description on Flickr or whatever image sharing service you use:
<a href="http://neilcreek.com/blog/2008/02/28/how-to-see-3d-photos/" target="top">Learn how to see 3D photos like this.</a>