Thursday, 27 March 2014

Understanding Camera Movements - Scheimpflug Adjustments

It is the Swing or Tilt movement of either standard of the view camera to precisely control the plane of focus in an image that is called Scheimpflug adjustments.

Scheimpflug Adjustments
Scheimpflug Adjustments

Swing movement refers to the movement of the lens panel or focusing screen or both around the vertical axis; similarly tilt movements are movements over the horizontal axis. Swinging or Tilting the the lens alters the plane of focus, there by modifying depth of field without in any way affecting the shape or position of the image.

In order to properly grasp the principle we should first familiarize ourselves with the three planes at work in any camera; the film plane, the lens plane and the plane of sharp focus.

Film Plane

Film plane refers to a flat imaginary palne at the rear standard of the view camera on which the film is fixed. Film plane extends well past the physical edges of the actual film.

Lens Plane

Lens plane is another flat imaginary plane that passes through the optical center of the lens and remains perpendicular to the lens axis.

The Plane of Sharp Focus

The plane of sharp focus is an imaginary plane positioned such that any object lying on it will be imaged sharply (by the lens) on the film plane.

In case of ordinary cameras without the capability for Swing or Tilt movements the three planes mentioned above will always be parallel to one another.

Scheimpflug Principle

Scheimpflug Principle states that if a lens is tilted in such a way that the lens plane and the film plane intersect, the plane of sharp focus must also pass through the same line of intersection; thus  a planar subject that is not parallel to the image plane can be rendered completely in focus.

Advantages of Scheimpflug Adjustments

Swing and tilt movements could be useful for taking detail shots of elevations photographed at an oblique angle. In such situations getting full depth of field is otherwise impossible even when the lens is fully stopped down.

Limitation of Scheimpflug Principle

The limitation of Scheimpflug adjustments is that they can only control depth of field across one specific plane of focus and this restricts their use in photographing three dimensional subjects.

Scheimpflug principle in Practice

In theory swing or tilt movents could be of either front or rear standard or a combination of both, it makes no difference as long as the three planes intersect at a common line. However in practice there is much difference; swinging the lens panel is limited to the covering power of the lens, similarly movement of the rear standard (film plane) alters the perspective especially of elements int he foreground.

So which standard you move should be based on the exact effect you wish to create, if getting a correct perspective is your priority then swinging the lens panel alone is the best way to increase depth of field. If perspective is not important then the best way to maximise depth of field along an oblique subject plane is to swing both the front and rear standards around the vertical axis in opposite directions so that the three planes intersect at an imaginary  common line.
Tilt movement works just the same except the movements are around a horizontal axis. Tilt movement is mainly used to increase depth of field along the ground rending areas from the foreground to the background in sharp focus even with relatively wide apertures. However as we pointed out earlier in the limitations of the principle, subject height above ground level is unlikely to be sharp (unless lens is stopped down).

Due to the limitations of the principle, and as we mostly deal with three dimensional subjects in architectural photography stopping down the lens is or using a wider anle lens advisable to increase the depth of field rather than resorting to schiempflug adjustments.

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