International Stereoscopic Union


A Glossary of Stereoscopic Terms

false stereo effects

Caused, e.g. in water or snow scenes, where one lens picks up a reflection which the other misses and this image is fused with a different reflection picked up by the other lens. Also caused by subject movement between two separate, sequential exposures; eg, drifting of clouds or branches blowing in the wind. See also accidental stereo effects.

far point

The feature in a stereo image which appears to be farthest from the viewer.

fifty-by-fifty (50 x 50)

Transparency mount size, referring in millimetres to images in normal 35mm slide mounts. A stereo pair in 50x50 mounts is usually referred to as 2x50x50 or 2/50x50.

five-perforation format

See format.

floating edges

Unnatural strips down the window frame of the scene where monocular images 'float', caused by the stereo window being located behind some or all of the subject matter. Masking (for transparencies) or trimming (for prints) the outside edge of the picture area gets rid of them by bringing the window sufficiently forward.

foil mount

A thin sheet of aluminium in a standard mount size, with window frames cut to the appropriate size for a given format, usually with some means of allowing each film chip to be held firmly yet also to be capable of re-positioning.

fore-window image

An image that appears in front of the stereo window frame; ie, "coming through the window". Where an image cuts the edge of the window-frame, the effect is usually referred to as floating edges.


In stereography, usually refers to the dimensions of the window-frame of an image pair, or the method of mounting the pair of images. For 35 mm transparencies, the format is often identified by reference to the number of film-edge perforations (P) in the width dimension of each frame, or by the name of the camera most closely associated with it; e.g., 4P (also 'Nimslo' or 'half-frame'); 5P (also 'Realist' or 'American'); 7P (also 'Verascope' or 'European); 8P (also 'full-frame'). Print formats are usually identified by the type of mounting; e.g., 'traditional' (for side-by-side pairs) or 'ViewMagic' (for over-and-under pairs).

frame identification notch

A notch on the top or side edge of, usually, the right-hand frame of some traditional stereo cameras, to provide a means of distinguishing it from the left-hand frame to facilitate mounting.


The adjustment of film chips in their mount(s) to include or exclude parts of the scene and to set up the stereo window.

In setting up for stereo projection, the sideways adjustment of the images so that the vertical edges of the frames are coincident.


Usually understood to mean the fusion of adjacent left and right image pairs into a stereo image without a viewing aid, by the ability to overcome the accommodation-convergence link, in order to diverge or converge the eyes (while they remain focussed at the viewing distance).
In the case of parallel viewing, the eyesight is made to depart from normal convergence so that the left eye looks only at the left image, and the right eye looks only at the right image.
With cross-eyed viewing, the left eye is made to look at the right image and the right eye at the left image (the images themselves being, of course, transposed from the normal arrangement). An advantage of the latter is that, once the technique has been mastered, larger and more widely separated images can be fused although it has the disadvantage of producing the effect of Lilliputism.

frozen water effect

The appearance (in a stereograph) of running water, particularly in rapids or a waterfall, when shot with too fast a shutter speed; noticeable because the image does not convey the expected sense of movement.

frustum effect (adv.)

Front-to-back keystone distortion in the space-image so that a cube parallel to the lens-base is portrayed as the frustum of a regular four-sided truncated pyramid with the smaller face towards the observer. In reverse frustum distortion, the larger face is forward.


The merging (by the action of the brain) of the two separate views of a stereo pair into a single three-dimensional (or Cyclopean) image.

fusion, irregular

Fusion of points that are not homologous, as with accidental and false stereo effects and multiple diplopia.



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