Basis (stereo photography)

In stereo photography , the basis describes the distance between two camera lenses .

The term includes not only the distance between two lenses of a stereo camera , but also the distance between the lenses of two cameras or between the lens of a single camera for time-shifted partial image recordings.

Base corresponds to the eye relief

In the case of a natural spatial effect in stereograms , the basis - like the average eye relief - is approximately 6.5 cm. With a base of this size, objects appear to the observer in their original size, but a spatial effect is no longer perceptible at great distances.

Lilliputism

If the stereographer chooses the base larger than the eye relief, the motif appears reduced on the one hand, and spatial perception at great distances is also possible on the other. Bases up to 20 m and more (depending on the focal length used and the near point) are not uncommon for capturing large landscapes . This effect is also known as lilliputism because of the reduction in size .

Gigantism

A small base (2 cm-4 cm) makes sense for close-ups, since it enlarges the subject (gigantism) and also normalizes the relationship between the object distance and base - and thus the deviation - and makes viewing easier.

Calculation of the optimal basis

The basis, or geometric relationships in general, for stereograms can be calculated using the following formula:

${\displaystyle {\frac {D\cdot a_{n}\cdot a_{f}}{f\cdot \left(a_{f}-a_{n}\right)}}}$

• ${\displaystyle D}$- maximum deviation
• ${\displaystyle a_{n}}$ - Distance of the closest point
• ${\displaystyle a_{f}}$ - Distance of the most distant point
• ${\displaystyle f}$ - Focal length of both lenses

If the distant point is at infinity, as is the case with photography of landscapes, for example:

${\displaystyle \lim _{a_{f}\to \infty }{\frac {D\cdot a_{n}\cdot a_{f}}{f\cdot \left(a_{f}-a_{n}\right)}}={\frac {D\cdot a_{n}}{f}}}$