Stereoviews were like televisions for the 19th century. People would relax in their parlor and be transported around the country and around the world with a box full of stereos and a hand-held or tabletop viewer.
The reason that people have stereoscopic vision is because we have two eyes. The eyes are on average about 65 mm apart, and so they see a slightly different image of the same scene. This is called parallax. Stereo photography relies on reproducing this parallax by taking two photos of the same scene (perhaps with two cameras) spaced apart (most often by about 65 mm). To see the photo stereoscopically, the left eye must view the image taken by the left camera, and the right eye must view the right image.
Most people use a viewer to force their two eyes to look at the two different images. However, it is possible to train your eyes to view stereoviews without using a viewer. This is called "Free" viewing. To see the stereo image, one should gaze off into the distance past the image. The eyes will relax and the two images should change into four. The images will not be in focus, but there should be four images. To see in stereo the two images in the very center of the image should become one image. Slowly adjust your focus to the center images while keeping your gaze in the distance. It is sometimes necessary to tilt your head left or right to adjust the horizontal alignment of the two images. Also, the images should be directly in front of you and about 12 to 18 inches away. Once you have the center image fused, you'll be able to move your eyes around to examine different details of the 3D image. The outer images will seem to be in the periphery and will not distract from your view of the central 3D image.
If you wear glasses first try keeping them on when viewing stereoviews. The correction in your glasses is usually necessary to allow you to focus on the images. But if it does not work, take your glasses off and try again.
The two dots form a stereo pair. In free viewing, you will see three dots -- the middle dot will pop out in 3D.
Aim your eyes between the two dots. Look through the image and into the distance. While aiming your eyes far into the distance, pay attention to what happens to the dots. You may see the two dots become three very easily. If that is the case, adjust to seeing 3D. Notice how your eyes feel and maintain the same feeling while you SLOWLY move your eyes downward to the center of the stereo picture.
If you see only two dots, you are probably looking at the dots themselves. Look through the dots. Try again. Aim your eyes between the dots and into the distance.
If you see four dots instead of three, you're almost there! Relax and aim your eyes further into the distance. Let your eyes drift outward and make the two middle dots slide towards each other until they merge or overlap. If you can't get the inside dots to move towards each other, you need to relax your eye muscles more. Imagine you are looking at an object very far off in the distance and keep trying. It takes Practice!
Simple Geometric Figures
Keystone "Eye Test" Stereoviews
Examples of Stereoviews With Receding Lines
Examples of Stereoviews With Receding Pairs of Lines
- Arbors and Alleys of Trees
- Bridges
- Rows of Columns
- Roads and Pathways
- Large Rooms and Hallways
- Tracks
- Tunnels
Examples of Other Stereoviews With Excellent Depth of Field