Perspective correction lens

From Wikipedia, the free encyclopedia

The world's first PC lens in the 35mm format: the 1961 F-mount 35 mm f/3.5 PC-Nikkor that shifts up to 11 mm in any direction.

The world's first PC lens in the 35mm format^[1]: the 1961 F-mount 35 mm f/3.5 PC-Nikkor that shifts up to 11 mm in any direction.

In photography, a perspective correction lens (also known as a PC lens, perspective control lens, or shift lens, or — if the lens can also tilt — a tilt and shift or TS lens) allows the photographer to correct for the effects of perspective by shifting the lens in relationship to the film or sensor area. This type of lens is mostly used in architectural and other technical photography. Perspective control lenses are generally made for single-lens reflex (SLR) 35 mm and medium-format SLR cameras, as most large format cameras allow for perspective correction using movements.

A perspective control lens has a larger image circle than is required to cover the image area (film or sensor size). Typically, the image circle is large enough, and the mechanics of the lens sufficiently limited, that the film plane cannot be shifted outside of the image area. However, all PC lenses require a small aperture setting to prevent vignetting when significant shifts are employed. PC lenses for 35 mm cameras typically offer a maximum shift of 11 mm.

The first PC lens manufactured for an SLR camera in any format was Nikon's 1961 f/3.5 PC-Nikkor. It was followed by an f/2.8 35 mm PC-Nikkor and an f/3.5 28 mm PC-Nikkor. Other manufacturers, including Olympus, Pentax, Schneider Kreuznach (produced as well for Leica), and Minolta, made their own versions of PC lenses. Olympus produced a 35 mm shift lens and a 24 mm shift lens. Canon produce 24 mm, 45 mm, and 90 mm TS lenses.

1 Applications
2 Available lenses
3 Perspective correction in software
4 Gallery of perspective correction lenses
5 References
6 External links

[edit] Applications

(a) Tilting the camera upwards results in vertical perspective.

(b) Keeping the camera level, with an ordinary lens, captures only the bottom portion of the building.

When making photographs of buildings or other large structures from the ground, it is often impossible (without shift) to fit the entire building in the frame without tilting the camera upwards. The resultant perspective causes the top of the building to appear smaller than its base, which is often considered undesirable (a). The perspective effect is proportional to the lens's angle of view.

Photographing from the ground, perspective can be eliminated by keeping the film plane parallel to the building. With ordinary lenses, this results in capturing only the bottom part of the subject (b). With a perspective control lens, however, the lens may be shifted upwards in relation to the film plane, placing more of the subject within the frame (c). The ground level, the camera's point of perspective, is shifted towards the bottom of the frame.

Another use of shifting is in taking pictures of a mirror. By moving the camera off to one side of the mirror, and shifting the lens in the opposite direction, an image of the mirror can be captured without the reflection of the camera or photographer. Shifting can similarly be used to photograph 'around' objects, such as a building support in a gallery, without producing an obviously oblique view.

[edit] Available lenses

In the 35 mm format, PC lenses for architectural photography have appeared in focal lengths of 24 mm, 28 mm, 35 mm, 45 mm, 85 mm and 90 mm. The earliest such lenses were 35 mm focal length, which is now considered too long for many applications. With advances in optical design, lenses of 28 mm and then 24 mm became available and were quickly adopted by photographers working in close proximity to their subjects, such as in urban settings. Nikon produce 24 mm and 85 mm PC lenses with both tilt and shift movements; the 85 mm lens offers close focus (0.5 magnification) for macrophotography. Canon’s TS-E lenses all offer tilt and shift movements; the 90 mm lens gives 0.29 magnification.

PC lenses are all prime lenses. They can be quite expensive compared to regular prime lenses. Some medium format camera makers, such as Mamiya, have addressed this problem by offering shift adapters that work with the maker's other prime lenses.

[edit] Perspective correction in software

Main article: Perspective correction

Computer software (such as Photoshop's perspective and distort functions) can be used to correct perspective effects in post-production, but cannot recover lost optical resolution in the more distant portions of the subject.

[edit] Gallery of perspective correction lenses

Olympus 24 mm f/3.5 Zuiko-Shift. 10 mm maximum shift. Mounted on an Olympus camera.	Nikon 28 mm f/3.5 PC-Nikkor. 11 mm maximum shift. Mounted on a Nikon F5.	Nikon 35 mm f/2.8 PC-Nikkor. 11 mm maximum shift.	Canon TS-E 24 mm f/3.5L. 11 mm maximum shift. 8° maximum tilt.
Minolta 35 mm f/2.8 Shift lens, 11 mm maximum shift.	Schneider 35 mm f/4 PA-Curtagon. 7 mm maximum shift. Also rebadged by Leica	Pentax Shift 28 mm f/2.8 SMC lens. 11 mm maximum shift.	Pentax Shift 6x7 75 mm f/4.5. 20 mm maximum shift. Mounted on a Pentax 6x7 medium-format SLR.