Stereo (3 Dimensional) Photography

The International Stereoscopic Union The official website.  

On this server:
  • Anaglyph Slide Show of Ísland (Iceland) by Michael Gordon, 1985-1986.  Small collection but will gradually be growing.
  • Pacific Northwest -- A stereo slide show; anaglyph (red left, cyan right).  Featuring Puget Sound and Seattle.
Links to other sites:

Normal photography creates the illusion of depth through the use of perspective and lighting.  Distant objects are smaller than nearer objects of the same kind; also, they are less distinct.  

Stereo photography re-creates the sensation of depth; not merely an illusion.  Slightly different images mimic what your eyes see when viewing an actual scene. Consequently, so long as you have normal depth perception, you will see depth. This phenomenon can be exaggerated (hyperstereo)producing spectacular scenes impossible to "realize" with normal photography or vision.

All techniquest seek one goal:  The left eye must see one image, and the right eye must see another image very similar.   This can be accomplished many ways.  The most direct method is with a hand-held viewer, such as a Kodaslide viewer, that have not been made since the 1950's.  Some beautiful, custom made (and expensive) viewers exist recently.  

Because of the unpredictable nature of a web page, anaglyph stereo is very popular on the web.  The left and right images are superimposed on top of each other; the seperation is made by colors -- red goes to left eye, cyan (blue-green) goes to right eye.  The seperation is not usually perfect and not suitable for high contrast subjects.

Viewing Methods:  
  • Group viewing: 
    • Projected, polarized viewing is the most common (perhaps only) method suitable right now for groups.  The idea is simple: you project the left image through a polarizer, and the right image through another polarizer rotated 90 degrees (1/4 turn).  The audience then uses spectacles that have polarizers in them.  The left polarizing lens allows the left eye to see only the left image, same for the right.  A tiny bit of "bleed" from one to the other often exists so the method has small problems with high contrast images.   It requires a screen capable of preserving polarization; that means an aluminized screen and NOT a glass-bead screen.
    • Crystal Eyes (trademark) and similar.  It uses two LCD (Liquid Crystal) lenses and is synchronized to a computer or projector.  For an instant, the left lens becomes transparent and at the same time, the left image is displayed.  Then the right image is displayed at the same time the right lens is transparent.   Synchronization rate must be very fast, around 100 Hz, and the persistence of the screen must be zero so as to not have a residue of the left image when the right image is being displayed.   When it works it is spectacular.
  • Personal or individual viewing:
    • Free-viewing; no device.  See below for more discussion.  It always requires two seperate photographs spaced side by side.  It can be done parallel (left eye to left image) or cross-eye (left eye to right image).
    • Lensed viewers for Realist format or 35mm film chips.  The Realist format holds both film chips in one carrier (glass, metal or cardboard); you hold the viewer to your face.  Quality is excellent.
    • Over/Under mirrored viewers allow stereoscopic viewing of extremely wide panoramas but require precise vertical spacing.  They are also very handy for snapshots; place two snapshots on a flat surface, right image above the left image, and look down on it with a mirrored over/under viewer.  
    • "Lorgnette" viewers are tiny prism divergers with a lens built in.  They suffer from a bit of chromatic abberation (because of the prism) but are convenient.   
    • Expensive side-by-side mirrored viewers are available from geology and earth sciences catalogs for viewing aerial photographs; they can view large, detailed stereoscopic images without abberations.  
Cross-eyed Freeviewing:
  • The image for the right eye is on the left, and the image for the left eye is on the right.
  • Cross your eyes willfully, so that your left eye is looking at the right image, and the right eye is looking at the left image, and a virtual image will appear in the middle and it will be stereoscopic and in full color.
  • It works better if you use tall and narrow images but no specific limitation exists beyond the ability of your viewers to cross their eyes; they can always back up for more distance to reduce eyestrain.     
  • One problem with this approach is that your brain interprets the parallax of your eyes (crossing) to mean that the image is very close to your face and thus the objects must be very small.   However it is very tolerant of different screen sizes.
Parallel Freeviewing:
  • Left eye to left image, and right eye to right image.  You look "through" the page or screen to achieve the stereoscopic center view.
  • Extremely difficult for many people to accomplish.  
  • The spacing of the images cannot be wider than your eyes.  Tall and narrow photographs are well suited to this format.  
Considerations for newcomers

Sooner or later, many photographers discover stereo photography, perhaps never knowing that it is more than 100 years old and well developed.  Many mistakes are made; small ones but easily avoided.  Here's a couple:

1.  Stereo Window.  

  • The frame of the stereo view forms a window, as if a window on a house, and you look through it to the subject.  Your brain does not enjoy seeing things that are cut by the edge of the window.  That cannot happen in nature.  A thing poking through the middle of the window is occasionally acceptable.  Fixing this problem nearly always requires careful cropping in a computer or careful framing in a camera.  
  • Stereo cameras automatically set the window at a distance of about 7 feet (2 meters).  If you are using one camera to take two photographs, you must cut the film chips in a way that is rather complicated to explain; the image for the left eye must be cropped slightly to the right as compared to the image intended for the right eye. The reason for this is to consider standing in front of a real window; your left eye sees more to the right of the scene through the window, and the right eye sees more to the left of the scene through the window.  
  • One method of setting the window is to observe the nearest object in the scene, and crop the film or digital image so that the edge (left or right) is identical with it on both images.  That places that object exactly at the plane of the stereo window.  
  • Mechanical aids exist when making film for projection; you can view the image and move the chips until it is perfect and then fasten it.  On a computer, you achieve similar results in various ways.  
2. Convergence: where to point
  • If you have a stereo camera, this is not an issue; both lenses point correctly all the time.
  • If you have one camera and take two images, generally speaking you point the camera in exactly the same orientation both times; or in other words, target something at infinity.  Trust me.  Otherwise what will happen is that if you aim the camera at somethere near for both photographs, things at infinity will view or project beyond infinity.  The reason is very simple: optical axis are parallel only for objects at infinity.  If you point the camera directly at a near object for both photos, when viewed, they will have the same angle on the film, ie, be parallel when viewed, hence at infinity.  Anything beyond the object will be beyond infinity. 

Updated 22 November 2004.   See /index.htm for feedback window.