International Stereoscopic Union The
On this server:
Links to other sites:
- 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.
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
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
- 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
- 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
- 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
- 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.
Considerations for newcomers
- Left eye to left image, and right eye to right image.
You look "through" the page or screen to achieve the stereoscopic
- 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.
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.
2. Convergence: where to point
- 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
- 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
- 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