I can't get this happening - because I can't 'defocus' my eyes all that well - read the instructions below.
Remember the 1990s craze of Magic Eye posters? Just like those, the spectacular space pictures in this gallery can be brought to life in 3D when viewers use a trick of the eye - with no need for special glasses. Stare into the screen and allow your eyes to defocus. You will get double vision as each eye sees the L & R images separately. Move your head towards and away from the screen until the two middle images overlap. The single overlapping image should be in 3D
via Derren Brown Blog
Originally from The Daily Telegraph