In 35mm photography, the most common use of shift lenses is for architectural photography. Normally if you use a wide angle lens to photograph a tall building by pointing the camera upwards, the building will appear to be tilted.
In other words, if the film plane is not perpendicular to the ground when photographing parallel vertical lines, the lines will not remain perfectly parallel in the photograph.
But when using a wide angle lens to photograph a building, if you keep the film plane perpendicular, i.e. keep the camera level, you will get too much of the ground in the picture and you might chop off the tops of the building.
One solution is to use an even wider angle lens, hold the camera level to the
ground, and then crop out the unwanted foreground when making your final
print. However by using this method you are wasting a substantial portion of the film area. Another
solution is to use a "shift" lens. Shift lenses borrow a concept from view
cameras, namely the lens can be moved off-center from the center point of the film.
Nikkor "shift" lenses for 35mm photography allow adjustment of the distance from the axis of the lens to the center of the
film via a thumbscrew which pushes the lens off-center.
Then if you shift the lens up when photographing a building, you will see more of the top of the building and less of the ground.
But since the film plane is still perpendicular to the ground when the lens is shifted, vertical parallel lines will remain parallel and the building will not appear to be tilting.
Below
are two sets of 3 photos intended to illustrate using shift lenses to control
perspective. In each case, all three photos are taken from exactly the same camera position.
The examples show a photo taken with an un-shifted lens, a photo with a shifted
lens, and an example of using Photoshop to imitate a shift lens by distorting
altering a photo taken with an un-shifted lens. It can be seen that Photoshop
techniques can produce a similar effect to using a shift lens but the
perspective is not completely identical. Either of the Photoshop techniques
(cropping and/or distorting) used below do waste a portion of the image area.
Aside from a restricted ability to make big enlargements, this also means that
if you wish to emulate a 28mm Shift lens you would need a conventional lens of a
maximum of 24mm, possibly wider.
Canon's "shift" lens also includes another adjustment called "tilt" which the Nikon shift lens does not have. The "tilt" adjustment refers to tilt of the lens and,
as I understand it, provides a means to control the focusing depth of field (DOF).
In the "shift" adjustment described above, the axis of the lens always remains perpendicular to the film plane. The DOF zone will always be perpendicular to the axis of the lens itself,
rather than parallel to the film plane. So when the lens is tilted, the DOF also tilts. In other words, in a normal case you might have a range of 3 to 5 meters in focus and this will be the same at both the top of the photo and at the bottom of the photo. But if you tilt the lens, it might be possible to have 3 to 5 meters in focus at the bottom of the photo and 5 to 7 meters in focus at the top of the photo.
Unfortunately I don't have any photographs to illustrate this concept but you
might be able to find some by searching elsewhere on the web.
Nikkor 28mm Shift Lens, lens in unshifted position but camera pointed
upward to be able in include all of the buildings
Nikkor 28mm Shift Lens, camera held level but lens
shifted
upward to be able in include all of the buildings. Photo taken
from same position as in the photo on the left
Same picture as on the far left (with unshifted lens) but
distorted (using "Transform" "Perspective") in Photoshop to compensate for the distortion caused by angling
the camera upward without shifting the lens.
Nikkor 24mm "Normal" Lens
Camera Held Level
Nikkor 35mm Shift Lens
Camera Held Level but lens shifted upwards
Photo taken from same camera position as the one on the left
Same picture as on the far left (with 24mm normal
lens) but cropped in Photoshop to eliminate foreground to get
almost the same view as in the center picture (with 35mm Shift lens).
Note that the image was only cropped and was not distorted nor transformed in Photoshop to alter the perspective
