Stereophotography

To obtain a stereo pair, it is necessary to remove the same objects from two different points, which are separated from each other horizontally within the stereo base distance. It does not matter in principle how these pictures were taken: in two steps with one ordinary camera , which is moved from one to point to another, with two paired identical cameras (“photo park”), or with a specialized stereo photo camera ^[2] . Another way of stereoscoping involves the use of a special stereo nozzle on the lens of an ordinary camera. Such a nozzle with the help of prisms or mirrors builds within the frame of the frame window an image consisting of two, obtained from different angles ^[3] . Specialized stereo cameras contain two or more lenses that shoot the same object from different points.

Each of the methods has its own advantages and disadvantages. The most simple is considered to be a regular camera shot, moved horizontally, sometimes along a special guide. However, this technique is unsuitable for shooting moving objects that have time to move between two exposures ^[4] . Two identical cameras for the same reason require precise synchronization of the valves . The most convenient shooting is with a specialized stereo camera, which in fact constructively combines two cameras with separate gates, but a common viewfinder and a tape path in a common case. Such cameras can contain more than two lenses, providing a multi-view shooting, designed for special demonstration technologies, allowing you to actually “look” at the main subject of shooting.

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  Folding stereo camera

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  Soviet stereo camera " Sputnik "

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  Camera with stereo lens

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  Soviet stereo camera " FED-Stereo "

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  Stereophoto "Nimslo"

The finished image can be observed without any devices ( parallel and cross stereopairs ), using a stereoscope , a dual overhead projector or on a flat print made by a lenticular print method or with a two-color anaglyph image. In a stereoscope, the separation of images of a stereo pair takes place at the expense of separate eyepieces for the right and left eyes. A lenticular print does not require any optical devices, and anaglyph implies the simplest glasses with red and green light filters. Moreover, the lenticular imprint allows for the presence of more than two angles of a stereo pair. In the case of diaprojection, separation is most often carried out by polarization using light filters on the lenses of the projector and glasses of the corresponding type ^[5] .

In most cases, during stereo photography, the distance between the optical axes of the lenses is assumed to be approximately the same as between the pupils of the eyes of an adult, that is 65 millimeters ^[4] . This stereo basis is considered standard. At the same time, in the finished image, the sensation of volume corresponds to the impression obtained by direct observation of the scene. However, if the entire subject being shot is removed from the camera further than 100 meters, on a normal basis the stereo image looks flat. The optimum volume sensation is achieved if the stereo base is approximately 1/50 of the distance to the subject of shooting ^{[6] [7]} .

For large distances and shooting vast landscapes, it may be necessary to increase the stereo basis to several tens or even hundreds of meters. Such shooting is possible with one camera, which is transferred from one point to another while preserving trimming, or with two cameras synchronized using a radio release. In extreme cases, the stereo basis due to the orbital motion of the Earth can reach millions of kilometers, reflecting volumetric astronomical objects ^[8] . Extended stereo basis is often used in aerial photography for photogrammetry . The most common technology is based on slotted aerial cameras , leading route shooting from two angles: ahead of the course and lagging behind. The resulting parallax can be up to several kilometers, providing excellent readability of the relief, even from high altitudes ^[9] .

Limitations

When choosing a wide stereo basis, the survey points should be located strictly at the same height, which can cause difficulties in areas with pronounced relief. When shooting with a single camera requires a strict immobility of all objects shooting. The quality of the stereo image can be reduced even due to minor fluctuations in vegetation, not to mention larger objects such as clouds. With a large number of moving objects, such as vehicles, the shooting should be done with two synchronized cameras at the same time. In this case, the focal lengths of the lenses and the trimming should be identical, and the exposure parameters should coincide ^[10] .

Unlike stereo images taken with a standard basis, Hyperstereo distorts the subjective perception of the plot sizes. Objects appear smaller than in reality, and closer than they were at the time of the shooting. With very large stereo basis, the impression of “toy” may be created ^[11] . The deep urban landscapes can seem like a set of flat scenery, placed at different distances from the observer. For these reasons, large stereo bases should be used only when necessary, mainly for application purposes. The most common use of hyper stereo is measurements on the ground with photogrammetry. Here, an enlarged stereo basis improves the accuracy of stereoscopic 3D modeling.

TeleStereo

The feeling of "toy" and "cardboard" can be eliminated by a proportional increase in the focal length of the lenses with an extended stereo base. In this case, the subjective dimensions of the objects in the picture remain normal, and the whole scene seems closer than it was in reality. For example, when using a long-focus lens , whose focal length is twice as long as normal , the stereo base should also be doubled compared to the standard 65 mm. In this case, in the picture, the objects of the survey seem to be twice as close as they actually were, while maintaining their normal size.

When shooting from distances closer than 2 meters, the parallax increases to values ​​that reduce the comfort of perception of the scene. From very close distances, a stereo pair is obtained, which becomes impossible to observe due to too large convergence angles ^[12] . Therefore, when macro photography, the stereo basis is reduced in proportion to the scale . The closer the subject is, the shorter the stereo base should be ^[7] . When shooting still objects, a reduced stereo basis is achieved by moving the camera between exposures. For shooting moving objects in different countries, special cameras were produced, for example, “Macro Realist”, suitable for macro photography at distances from 10 to 15 centimeters.

Another way to stereo macro involves the use of a flatbed scanner. At the same time, the object is scanned twice, and each time it is placed on a glass slide in slightly different positions.

• Holography

• E. A. Iofis . Photo kinotekhnika. - M .: “Soviet Encyclopedia”, 1981. - 449 p. - 100 000 copies

• S. V. Oleinik, V. B. Gaida. Digital cameras for aerial photography (rus.) // Geoprofi: magazine. - 2006. - № 4 . - p . 45-51 . - ISSN 2306-8736 .

• N. D. Panfilov, A. A. Fomin. Viii. Special types of shooting // Quick reference photo amateur. - M .: "Art", 1985. - 367 p. - 100 000 copies

• Jacob Perelman . Sight with one and two eyes // Entertaining physics . - M .: "Rimis", 2015. - T. Book 1. - 208 p. - ISBN 978-5-9061-2217-9 .

• S.N. Rozhkov, N.A. Ovsyannikova. Stereoscopy in film, photo and video equipment / V. I. Semichastnaya. - M .: "Paradise", 2003. - 136 p. - 1000 copies - ISBN 5-98547-003-2 .

• E. D. Tamitsky, V. A. Gorbatov. Chapter I. Technique of photographic shooting // Educational book on photography / Fomin A.V., Fivensky Yu. I. .. - M .: “Light Industry”, 1976. - P. 7-128. - 320 s. - 130 000 copies

• Stereo Geometry
• “How to shoot 3D” // World of 3D / 3D World. № 2. 2011 (inaccessible link)