Stereoscopic Photography...the Science of Solid Viewing

Close up and Portrait

Static Subject Close Up

In the case where the subject cannot move a single camera a traverse is used. First the left exposure is made then the camera is traversed over for the right exposure. This single camera allows the photographer freedom to select focal length and traverse distance: indeed the wide angle lens is rarely used below 1.5 metres.

For a subject distances greater than 1 metre (try to make it 1.5 metres):-

Traverse distance (mm) = 93 x (28/ Focal Length) mm.

When we look at close objects our eyes angle in and focus on one part of the object and toe in slightly. The effect of this action is to optically bring our eyes closer together. Because the picture is a general scene and not just a single part of one object we cannot practically toe in the cameras. The only thing to do is to reduce the traverse distance. Another unfortunate effect of viewing close range flat pictures is that the scene will `bow up' slightly in the middle.

When working at 1 metre and closer long focal length lenses will normally give better results. These lenses effectively magnify the picture hence the traverse distance must be reduced appropriately. This keeps the parallax correctly related to the perspective.

For a subject closer than 1 metre use following general close up guide formula:-

Close up traverse in mm = 93x (28/Focal Length) x (Object distance in mm/1000).

The `subject distance' is considered to be the `subject to the lens optical centre distance'. For long 35 mm zoom lenses set on macro this may be hard to determine. (I use a computer program that converts this distance to the distance from the subject to the film plane.) For digital cameras with their very short normal focal lengths these two distances are almost the same.

For much of my very close up work I use a digital camera: an Olympus C8080. This camera has a focal length that is 0.25 the focal length of a 35 mm camera. But for practical purposes it may be considered to be an immediate process 35 mm camera with a zoom lens of 28 mm to 140 mm and macro or super macro options. However this zoom lens does not give the operator focal length directly - this parameter must be deduced from the picture width and camera to subject distance. A simple sighting protractor and look up chart allows the correct traverse to be determined easily.

This stereoscopic system is based on a picture width to height aspect ratio of 1.5 (This is about how we see the world.) Digital cameras have an aspect ratio of 1.33, which leaves white bars on either side of the prints. Fortunately they do not seem to matter in the stereoscope.

Close up prints contain considerable areas unique to the left and unique to the right areas that must be masked out to avoid viewing discomfort. (Pictures taken at greater than 3 metres when printed as `5 x 7 inches' from their true size of `5x7.5 inches' conveniently crop out these unique areas.)

The picture below shows a camera traverse with a digital camera mounted upon it.

 

Portrait

For any live or subject that can move, even very slightly, that lies in the subject to camera range of about 2.5 metres down to 1 metre (or even 0.8 metre) a different camera arrangement is use. The cameras are rotated by 90 degrees. This is called the portrait arrangement; it should really be the `generic portrait' arrangement.

This stereoscopic system is based on prints called the 5x7 inch size; taken with two 35 mm wide angle (28 mm) cameras nested together. Alas this nesting requires that the cameras be staggered by 30 mm which causes some left versus right perspective distortion. This distortion results in viewer distress for pictures taken closer than about 3 metres from the subject ( actually 2.5 metres is OK). The portrait mode removes the stagger for this special case, but it is a compromise.

The picture below shows the cameras mounted in the `portrait mode'. Here the cameras have been rotated by 90 degrees, fitted with 50 mm lenses and mounted without stagger with their film centres about 67 mm apart. Thus the correct perspective and parallax relationship have been maintained.

However the resulting prints are now vertical instead of being horizontal; yes they go into my viewer as special mounted prints but they look weird. The top and bottom need to be cropped off by 25 mm each to fit the 126 mm (5 inch) high stereoscopic format. To prevent viewer distress the unique left and unique areas of view need to be masked off and the whole thing correctly centred on a black `5x7' size card mount.

The result of this operation is nice almost square stereoscopic portrait that delights the eye and is compatible with the viewing belt system.