Scheimpflug principle

Scheimpflug principle. In geometric optics, it is a condition describing the orientation of the plane of focus of an optical system when the lens plane is not parallel to the image plane. This principle enables the extension of depth of field along a tilted subject plane, a technique critical in view camera operations and modern tilt-shift photography. It is named for its discoverer, Austrian cartographer and inventor Theodor Scheimpflug.

Definition and basic principle

The principle states that when the lens plane, the subject plane, and the image plane intersect along a common line, the entire subject plane will be rendered in sharp focus on the image plane. This geometric condition allows photographers to overcome the limitations of the traditional depth of field, which is parallel to the sensor plane. The concept is foundational for controlling perspective distortion and achieving selective focus in technical and artistic photography. It fundamentally alters the relationship between the optical axis and the film plane in a controlled manner.

Geometric formulation

Mathematically, the principle can be described using the Hinge rule, which is a consequence of the intersection of the three planes. If the lensboard is tilted or shifted relative to the film back, the plane of sharp focus rotates accordingly. This formulation is applied in the design of tilt-shift lens mechanisms for 35mm film and digital SLR cameras. The precise angular relationships are calculated using principles from descriptive geometry and are integral to the operation of devices like the Sinar system. Understanding this geometry is essential for practitioners of architectural photography and product photography.

Applications in photography

The primary application is in view camera movements, particularly tilt and swing adjustments, used extensively in large format photography. It enables landscape photographers to achieve front-to-back sharpness without resorting to extremely small aperture settings. Conversely, it can create a miniature faking effect by restricting the plane of focus. The principle is implemented in specialized lenses from manufacturers like Canon, Nikon, and Pentax for digital photography. It is also crucial for correcting converging verticals in images of tall structures like the Empire State Building.

Applications in other fields

Beyond photography, the principle is vital in aerial photography and photogrammetry, where it corrects for distortions caused by aircraft attitude, a technique pioneered by organizations like the United States Geological Survey. In machine vision and optical inspection, it is used to maintain focus across uneven surfaces on assembly lines for companies like Siemens and General Motors. The principle also finds use in certain laser scanning configurations and confocal microscopy techniques developed at institutions like the Massachusetts Institute of Technology. Its geometric rules are analogous to those used in some 3D reconstruction algorithms.

History and development

The principle was first articulated by Austrian naval officer Theodor Scheimpflug around 1904 while developing rectification techniques for aerial survey purposes. His work was aimed at improving the accuracy of cartography for the Austro-Hungarian Navy. The concept was later refined and popularized within professional photography through the writings and camera designs of innovators like Ansel Adams and the engineers at Hasselblad. The commercial introduction of the PC-E Nikkor lens series by Nikon Corporation brought the principle to a wider audience of digital photographers. Its underlying optics were further analyzed in publications by the Optical Society of America.