Stereoscopic Photography...the Science of Solid Viewing

The Cameras

Synchronized and Mated Pair

Two old style 35mm Pentax ME cameras with manual setting are used (**). These are nested and clamped to a frame that ensures their parallel alignment. The cable shutter releases are brought to a common operating point and so arranged that the left hand camera triggers a few milliseconds before the right.

The simple object of stereoscopic photography is to show the whole scene and allow the viewer to select the section of interest for themselves. To this end wide angle lenses of 28 mm focal length ( 64 view laterally) are used with small aperture to ensure considerable depth of field. Since the individual parts of the scene are small they must be of high resolution hence the need for fine grain film and careful processing. I usually use AGFA ISO 100 or 200 negative and AGFA 100 positive (*). Normally the camera frame is mounted on a tripod to ensure that camera shake is minimized and to carry the weight of the unit (2.5 kg). The objective here is to obtain a 2000 + lines (high definition) image within the 24 x 36 mm frame. This high resolution is an objective, not always achieved or even needed.

Because stereoscopic pictures are necessarily depth pictures it is normal practice to work with fairly small apertures in order to get the depth of image field. The use of wide angle lenses greatly enhances the depth of field but it still requires apertures from F5.6 to F16.

Flash pictures are possible using the cameras set to 1/60 second, to allow more timing margin. The flash unit is triggered from the right hand camera with the left shutter guaranteed to operate just a head of the right (1 to 5 milliseconds). (I achieve this most of the time.) An electronic synchroniser is available but this can become just one more encumbrance.

The nesting of the cameras allows the lenses to be a minimum of 94 mm apart laterally with the left behind the right by the thickness of a camera, 30 mm. Our eyes are 60 to 65 mm apart laterally and side by side, so the cameras are wrong? Yes indeed but the action of the viewing equipment will partially compensate.

With wide angle pictures the scene is compressed laterally and consequently the depth perspective is expanded. Setting the cameras wider than our eyes tends to compensate for the lateral compression.

The left hand camera depth offset (30 mm) is indeed nasty and has to be accepted. To avoid viewer discomfort with left versus right perspective distortion major parts of the scene should not be closer than 2m, though minor parts can be less. At 3m (1% perspective distortion) the depth offset distortion affect is almost negligible (or shall we say that our eyes can tolerate it).

Digital Cameras

High definition digital cameras could be used. The type that have a lens mount right at the end of the camera body; then inverting one of the cameras so the lenses come side by side. This would require a carefully designed and made mounting frame. However suitable digital cameras are very expensive and so are priced well beyond the needs of this project.

The Lateral Traverse Single Camera

For this case a single camera is used. This Camera is mounted on a sliding traverse device that permits the camera to be moved sideways for sequential left and right exposures. This device permits any traverse distance to be selected, any camera to be used with any lens. No careful matching, aligning or offset troubles. Because the two exposures are significantly separated in time the subject must be truly static; for the slightest movement of any part will cause stereoscopic distortion.

Perspective is related to focal length and parallax to the traverse. The two must match our eye lenses and their distance apart (nominally 60 mm). This leads by a circuitous mathematical route to the following guide formula for this system of cameras and stereoscope:-

Traverse distance (mm) = 94 x (28/ Focal Length mm). (NB. For this system only)

This relationship holds true for any subject to camera distance down to about 1 metre. Close up work comes under a different heading.

The single camera traverse allows great flexibility of use, but only with truly static subjects. Sometimes I remove my old film Pentax and substitute an Olympus C8080 digital camera. (Instant images are so nice and reassuring.)

The following picture shows a typical single film camera traverse arrangement.

 

Portrait Set up

Portrait here is a generic tern that I use to describe any photo where the twin cameras have been rotated by 90 degrees. In this system the portrait set up is only used when the subject to cameras distance lies in the range of 3 metres to 1 metre (perhaps 0.8 metre). The resulting prints are awkward and have to be cropped; but they do permit side by side cameras with out the stagger distortion. Hence this set up allows close up photography of live or moving subjects. The details of this arrangement are in the section Close Up and Portrait.

The following picture shows a typical portrait camera setup.

 

Point and Shoot

There is a practical problem with all this equipment, it is cumbersome and heavy. It takes time to set up, plan shots, measure exposures and distances. It is good for deliberate planned photography but out of the question to just carry it around. For just having on hand something far simpler that works well enough is needed. Such as a `point and shoot' on a very simple traverse with a small light weight tripod as the following picture shows.

(**) Scenic Slide Pictures

For taking scenic slide pictures where resolution is vital, Contax cameras with Zeiss Distagon lenses and Agfa RSX diapositive film are used. With a heavy tripod and a synchronised electric shutter release the picture resolution approaches the resolution limit of the film and the camera optics.

(*) Film Type

This is of course a personal preference for two reasons: