What is the optical axis in photography?

The center line of a beam (column) or the axis of symmetry of an optical system. The observation optical axis is located next to the optical axis of the photographic lens and parallel to each other.

Axis shift, as the name implies, means that the optical axis of the lens can move, including the movement of the optical axis and the rotation of the optical axis, thus changing the perspective effect of the picture, including blur and distortion. The original intention of shifting the axis of a large frame is not to shoot creative effects, but to ensure that the camera has a clearer depth of field range and more accurate distortion control in a large frame.

The main feature of axis-shifting camera lens is that the main optical axis of the whole camera lens can be translated, tilted or rotated on the premise that the plane position of the camera body and the film remains unchanged, so as to adjust the perspective relationship of the shot image or focus the whole area.

The reference clear image field of the camera lens with shifting axis is much larger, which is to ensure that the main optical axis of the camera lens can still get a clear image after translation, tilt or rotation.

Extended data

Optical axis classification

1, astigmatism axis

The astigmatism axis represents the axial direction of the lens according to the direction in which your cornea has the greatest curvature and the weakest refractive power. Whether the line in a certain direction seen by the astigmatism eye is clear or fuzzy depends on the axial direction and degree of astigmatism. Generally speaking, the direction of the blurred line on the astigmatism eye surface is the axis direction of the negative lens worn by the eye.

2. Secondary optical axis

Short axis refers to any straight line passing through the curvature center of a single spherical mirror but not through the aperture center (vertex) of the spherical mirror. For a thin lens, when the refractive index of the space where the incident light is located is the same as that of the space where the outgoing light is located, any straight line passing through the optical center but not through the curvature center of the refractive sphere is a secondary optical axis.

3. Main optical axis

The principal axis is also called the "principal optical axis". A straight line passing through the centers of two spherical surfaces of a lens is called. The optical axis of a single spherical mirror is a straight line passing through the center of the spherical surface and perpendicular to the mirror surface; The optical axis of the lens or coaxial optical group is the connecting line of the spherical center of each lens. It should be noted that any straight line passing through the optical center can be called the optical axis of the lens, and they are generally called sub-optical axes.

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