How To Free View Stereoscopic Pairs

written for the stereosite by Steven Nossiter, USA

There are two types of stereo­scop­ic pairs, par­al­lel view and cross view. Par­al­lel dis­plays the images with the right and left images aligned with the right and left eye. Cross view swaps right for left and requires that you cross your eyes to see the 3D effect. All tra­di­tion­al stereo cards are par­al­lel view, and I enjoy being able to pick up a card and just free view it.

Theory

Nor­mal view

When you first look at a stereo image pair, your left eye and your right eye each see the entire card, and your mind assem­bles that into one view of the entire card; a nor­mal view. 

Dou­ble vision

When you allow your eyes to each focus on their ‘own’ side of the pair then each eye still sees the pair of images as they diverge, thus caus­ing dou­ble vision. 

Merge 

This appears as three (or four) frames until you suc­ceed in men­tal­ly merg­ing the cen­tral, 3D image, and ignor­ing the out­er frames. 

Unfor­tu­nate­ly, this infor­ma­tion is not espe­cial­ly help­ful when learn­ing to free view because the tech­nique is not so much intel­lec­tu­al as it is phys­i­o­log­i­cal and psy­cho­log­i­cal. But the fol­low­ing prac­tice guide might be help­ful. Though, don’t expect to be suc­cess­ful at the first time. You might be. Oth­er­wise, take time…

Practice guide

I have to say that any writ­ten expla­na­tion of how to free view is dif­fi­cult, because the tech­nique varies a bit from per­son to per­son, and it is sim­ply dif­fi­cult to explain in words. Last but not least, free view­ing has some advan­tages, but is not nec­es­sary if you have a viewer.

Sit in a com­fort­able chair that allows a sta­ble posi­tion rel­a­tive to the screen. Set up the stereo image about 5.5 to 6 inch­es wide (14 to 15 cm), lev­el with the eyes, and at least arm’s length away to start (some­thing like 24 to 28 inch­es; approx. 66cm). Some peo­ple may like to be far­ther away; the cen­ters of the images should appear the same dis­tance apart as your eyes.

Close (or block) your right eye; gaze at the left image with your left eye. Then switch: close (or block) your left eye; gaze at the right image with your right eye. Repeat, slow­ly sev­er­al times. When each eye set­tles eas­i­ly on its image then with one eye open, smooth­ly open the oth­er eye with­out try­ing to focus — just gaze. Relax, and don’t attempt to con­cen­trate, just allow the eyes to do what they do. You will see three images. With­out chang­ing the focus or direc­tion of either eye, focus your mind on the cen­tral image. It will give the impres­sion of depth to a greater or less­er degree. With prac­tice you will be able to men­tal­ly block out the indi­vid­ual images and only see the 3D cen­tral image.

The first cou­ple of times you may find your eyes chang­ing back to nor­mal focus, to see the pair as a pair. If you dont see what I’m describ­ing after try­ing sev­er­al times, try to relax and gaze over the top of the screen, maybe imag­in­ing you are look­ing across a room or out a win­dow, just day­dream­ing. With­out chang­ing focus allow your gaze to move down to the stereo image pair, and you will see three images. Relax, let go of all expec­ta­tions and the images will con­verge until you see the cen­tral image become 3D.

For Cross View, use the same sequence as in the first method, only with right eye to left image, and vice ver­sa.  With a lit­tle prac­tice you will expe­ri­ence a whole new dimen­sion of photography!

These rather sim­ple graph­ic images are cho­sen to allow easy par­al­lel free viewing:

If you are able to free view these stereo pairs try the fol­low­ing photo.