The basic idea is that you must get one eye to look at one of the image pair, the other eye at the other. Slight differences in the pictures provide clues which your brain interprets as depth information to create the sense of range. To do this 'split imaging' you either look beyond the pictures (as in the popular stereograms that look like a jumble of colors until you look beyond them), or look in front of the image pair (cross your eyes). The idea is illustrated in the following drawing.
When you first start trying to split the view you should see a partial 'phantom' image(s) appear between the two real images. Keep your attention on this phantom image(s). Try to change the distance you are looking at so the phantom image(s) becomes wider. If you see two phantom images try to align some prominent feature in them more closely. At some point, when the phantom image is nearly as wide as a real one (or the two phantoms are more nearly aligned), the stereo will 'jump' into view, and you will see three complete images with the middle one in stereo. The depth illusion is quite strong, so you won't have any doubt when you've got it right. After some practice the jump comes much more readily, and you feel much more comfortable.
For skill development you may use the 'Practice Views' below in which image pairs are graded in size. Start by getting the small images (1) at the upper left into stereo, then simply drop your gaze to the next row (2, 3, 4, etc). Once a bit of skill is acquired you may start at the upper right (3), and continue with even larger images in the right column (8, 9, etc). You may also start with higher numbered images, once you have some control and know what you're trying to do.
Once you see in stereo you can tell, from the small images (1) in the upper left corner, whether you are using cross or parallel mode. View 8 is about eye separation (65 mm), so if you are using parallel mode and start having trouble about there you shouldn't be too surprised. Few people can make their eyes splay apart beyond the parallel by more than a few degrees.
In the pictures on the calling page for this Help screen the left pair of a three image set are arranged for one mode, the right pair for the other. The center picture is used for both modes. The outside picture for the mode you're not using should be ignored.
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