Shift lens

Shift lenses can only be used with single-lens reflex cameras , as they require pass-through vision, which is not available with other types of viewfinder ^{[* 1]} . The main difference of a shift lens, which is much more expensive than conventional lenses, is the margin of the image field , which is significantly higher than that required for the frame format for which this lens is designed ^[3] . Moreover, the optical characteristics of the resulting image should remain uniform throughout the field, including at its edges. This is necessary when shifting the optical axis of the lens from the center of the frame window, in which vignetting and degradation of resolution should not be observed. The greatest difficulty in increasing the image field is for wide-angle shift lenses, since it requires an additional extension of the angle of the field of view . For example, the field of view angle of a conventional lens with a focal length of 35 mm, calculated on a small format frame, is 63 °, while a similar shift lens should provide up to 80 ° ^[1] .

Another difference, most noticeable externally, is the complex design of the frame, which allows you to move the optical unit in addition to the longitudinal direction of focusing in the transverse directions with high accuracy ^[4] . Most often, a special guide and a micrometric screw with the possibility of fixing in any intermediate position are used for shear ^[5] . In a similar way, a slope is controlled, which is performed due to the presence of curved surfaces of a cylindrical profile moving relative to each other. Installing the screws in the "zero" position turns the shift lens into a normal one, without shift and bias ^[6] . In addition to the guides, the frame of the shift lenses has a hinge for rotation around the longitudinal axis, for changing the plane of shift and slope. In this case, the optical unit with guides freely rotates relative to the shank of the lens, allowing you to perform a shift and bias in any direction ^{[* 2]} . The movable design of the frame in most cases forces one to abandon the mechanical drives of the jumping diaphragm and transfer its value to the TTL exposure meter . Most shift lenses (for example, almost all PC-Nikkor), until recently, were equipped with a preset aperture mechanism and allowed measuring exposure only at the working hole. More modern lenses are equipped with a jumping diaphragm electromagnetic drive that interfaces with the camera via an electronic interface . In addition, none of the shift lenses support autofocus .

The most widespread are shift lenses designed for small format and, to a lesser extent, medium format frame . Almost all large-format and some medium-format cameras, as a rule, provide for the possibility of movement due to the design of the case.

The world's first PC-Nikkor 3.5 / 35 shift lens was released in 1962 by Nippon Kogaku KK ^[7] . In the USSR, the first PKS Mir-67N 2.8 / 35 shift lens was developed at the Arsenal plant in 1990 ^[1] . In 1993, he was given the name "PKS Arsat-N", later replaced by the modern "Arax".

The technique of shifting and tilting shift lenses is similar to shooting with format cameras that allow movement of the objective board. The difference is the impossibility of shifting and tilting the cassette.

The widest possibilities are possessed by lenses which, in addition to shift, allow the tilt of the optical axis ( English tilt and shift ). This design makes it possible to depict simultaneously sharp objects located at different distances without reducing the relative aperture of the lens ^[8] .

In addition, the bias provides additional possibilities for correcting perspectives, including in interior and subject photography . At the same time, the bias violates the parallelism of the planes of the sharp image and the frame window, leading to the illusion of a shallow depth of field when shooting a landscape , reminiscent of a picture in macro photography . As a result, the usual urban landscape becomes like a smaller layout ^[9] . Slope to extreme positions can also be used with panoramic shooting ^[1] .

Compared to direct-view cameras , shift lenses provide limited perspective correction and image transformation capabilities. Most direct-sight cameras, especially cardan cameras, allow movement and slope in all planes of both the objective and cassette parts. Shift lenses allow you to use the shift and tilt of the lens only and only in one plane. To get the movement in another plane, the frame is rotatable. Tilt-shift lenses allow you to combine slope and motion, as a rule, in mutually perpendicular planes ^{[* 3]} .

Today, the most common shift lenses have focal lengths of 24 mm, 28 mm, 35 mm, 45 mm, 85 mm and 90 mm.

Expensive shift lenses can be partially replaced by a shift adapter, which is a sophisticated version of a conventional adapter that allows you to use lenses with a connection standard that does not match the one used in the camera. Shift adapters allow shooting only with optics designed for a larger frame size, since the shift requires a significant margin of the image field of the lens. In addition, the working segment of the lenses should be longer than that of standard optics, since the adapter design has a significant length.

This technology limits the use of shift, since it allows you to mount relatively telephoto lenses, little in demand in architectural photography . The correction of perspective distortions is of greatest relevance for shooting with wide-angle optics. However, when using wide-angle lenses designed for a larger format, they become normal at a reduced frame. So, lenses with focal lengths of 45–65 mm are considered wide-angle for the medium format 6 × 6 cm. When installing such a lens through a shift adapter on a small-format camera, the used field of view angle corresponds to a normal lens. Focal lengths of 24–28 mm, most in demand in architectural and interior photography, are shorter than the medium format “ fish eye ” 30 mm. The maximum practical effect is achievable when using shift adapters for slope, which is popular because of the possibility of shifting the plane of a sharp image.

Among amateur photographers, the simplest tilt adapters, which are a ring with non-parallel lens and camera mounting flanges, have become widespread ^[12] . The ability to rotate the adapter with the lens relative to the camera allows you to move the plane of the sharp image, choosing its optimal position. An even cheaper alternative to shift lenses is the Lensbaby system, which allows you to use bias in any direction. The disadvantage of the system is a small aperture and poor image quality, unacceptable for professional photography.

• Lensbaby
• Perspective correction
• “ Horizon-205 ” is a panoramic camera with a shift lens.

• B. Bakst. Shift for the better (rus.) // “Photocourier”: magazine. - 2005. - No. 10 (106) . - S. 20-30 .

• How to make Novoflex? (Russian) // “Photocourier”: magazine. - 2005. - No. 6 (102) . - S. 3-9 .

• A. Trachun, N. Kalinina. Shift lenses of the Arsenal plant (Russian) // “ Photography ”: magazine. - 1995. - No. 3 . - S. 45 . - ISSN 0371-4284 .

• John Hedgecow. The photo. Encyclopedia / M. Yu. Privalova. - M .: "ROSMEN-IZDAT", 2004. - 264 p. - ISBN 5-8451-0990-6 .

• Hawkins E., Avon D. Photography: Technique and Art / A.V. Shacklein. - M .: "World", 1986. - 280 p. - 50,000 copies.

• M. I. Shulman. Cameras / T. G. Filatova. - L.,: "Mechanical Engineering", 1984. - 142 p. - 100,000 copies.

• School of studio photography (Russian) // "Photography" : magazine. - 1992. - No. 9-10 . - S. 42, 43 . - ISSN 0371-4284 .

• Using 35mm shift lenses
• How Shift Lenses Change your Life
• Hartblei Tilt and Shift Lenses