عدل أبعادك بعدسة ضبط الأبعاد ( p.c ) .. مجلة فن التصوير اللبنانية _ ع٦١

Adjust your dimensions with a Dimension Adjustment (P.C) lens.

The photographer often finds it difficult to achieve some images without tilting his camera in a certain direction, but even this measure may lead to the appearance of the subject tilted ... In this field and other areas that are more accurate, he may need a new type of lens bearing the name of the Perspective Control lens. (P.C).

Do you need (PC)? .
Yes, you need it if you, as the owner of a 35 mm reflex camera, have previously photographed a building, and ended up with a print or slide showing converging verticals and a building leaning backwards. What we mean by (PC) is the (P.C) lens from (Perspective Control).

This, and in order to obtain a complete structure in a photographic image using a regular lens, the photographer generally tends to tilt his camera upwards, which leads to the appearance of the structure.
tilted in the final image, and if a wide-angle lens is used, the image may include the whole structure despite holding the camera level, and that is in the vertical structure in particular, although it happens in this case that the image also includes a wide frontal area - which is not usually pleasant - when using such a lens wide angle. The building appears smaller. An alternative is to operate (PC) wide-angle.
Dimensional adjustment lenses are specially designed lenses with interface sectors that can be shifted from the middle center in several different patterns. Typical lenses for a 35 mm camera structure have an image circle with a diameter of approximately 43 mm or slightly larger. These are completely sufficient to cover the rectangle of the 24 x 36 mm structure, as shown in Figure - 1. As for the lens with the smaller image circle, it will lead to brevity, i.e. blurring the corners of the image, while the (PC) lenses designed with wider image circles. Typically, it ranges from 57 to 63 mm as the length of the diameter - it allows moving the front of the lens away from the axis while preserving the appearance of a complete image on the flat film, as shown in Figure -2-.

Photographers working with 35mm cameras are rarely interested in information about the diameter of the image circles in their lenses.
While the users of the single view camera intend to disclose the information of the image circle in the lens specification maps because of the mechanics of vibrations, transformations and representation in the single view cameras. That is because any movements away from the axis will transform the image, and it takes a wider image circle to keep a complete image on the image plane, and the ability to make these movements and obtain correct dimensions is the reason why the single view camera (view camera) in general is the camera that is chosen.
In architectural and interior photography.

In order to preserve the images when photographing the buildings on the perpendicular as they are, vertical, the flat film must be parallel to the buildings, and if it is not, a distorted image will be produced. Here comes the (PC) lens for the 35 mm camera, allowing the film plane to remain parallel to the main subject: that is, the front conversion edges in it allow the top of the building to be included. An example of this is that with the use of a (PC) lens of 28 mm, the building was photographed in Figure 30, while the camera was completely flat and the flat film was parallel to the building. Note the large space for the front, while in Figure -40 - the camera is tilted to bring out the front and include more of the building.
Notice the building's inclination backwards. As for Figure 5, the flat film remained parallel to the building, while the direction of the lens was shifted to its maximum position, which is approximately 11 mm.
However, the PC lens has other uses than just photographing tall buildings. Indoor locations, which are tall and spacious rooms in particular, are typical subjects here, as shown in the figure. For this shot, the lens direction was shifted to remove a gallery space and capture a wide wall mosaic. Most PC lenses can be rotated to allow for horizontal, diagonal, and downward shifts, as well as vertical upward shifts.
Horizontal and diagonal shifts allow the photographer to take pictures that exclude, within limits, unwanted objects in the foreground, such as telephone poles, people, and anything that cannot be carried outside the scope of the image. For example, when photographing reflections in windows, the photographer himself is often An undesirable reflection. By using a (PC) lens with a horizontal or diagonal conversion, the same image can be captured without including the photographer's reflection.

The (PC) lens also works as a great panoramic lens. In order to take panoramic pictures, mount the camera flat on a stable tripod, turn the lens horizontally towards its maximum conversion, then take the picture, then rotate the lens carefully and carefully for a distance of 180 degrees, and take another picture . The two images can be completely combined to create a panoramic image that would not be possible otherwise except with the use of a lens with a much wider coverage angle, or by using a special panoramic camera. One of the advantages of using a (PC) lens is that the subjects in the panoramic view taken with a (PC) lens will be larger than that In the wide angle panoramic shot.
Not all PC lenses are created equal. They vary in terms of focal length, maximum and minimum aperture, and image circle diameter. And the distance of conversion and rotation.
In addition to containing a conversion of 11 mm. The Canon 35mm f/2.8 lens allows its user to represent the optical axis off-axis by eight degrees when the lens is placed on zero conversion. Thus achieving an increase in depth of field. This is particularly useful for subjects on a table page and subjects in close proximity.

The Minolta CA 35mm f/2.8 conversion lens is unique in that it includes Variable Field Curvature (VFC) and is the only conversion lens with an automatic aperture. While most lenses are designed so that the focus orbit Precise is flat. The VFC feature allows the photographer to adjust the flatness of the focus field, thus producing a precise focus with a curved orbit. This is great for three-dimensional subjects, but you should practice using this feature because when the lens is in a shifted position, the VFC does not produce a symmetrical change in the field.. That is, the field curvature is symmetrical only while the lens is unshifted. Read the instructions below. Come
with the lens.
We point out here that the only producers that manufacture PC lenses for more than one camera mount are Zeiss, which produces the Distagon (T) 35mm f/2.8 for Contax and Yashica, and . Schneider manufactures the 35mm F/4 Kertagon for most major carriers, including the Laicao Practica, Exacta, Miranda, Elbariflex, and Contarex.

As for the Olympus PC lens, it has a Zuiko 24mm f/3.5 conversion. It has the shortest focal length and widest angle of coverage - 84 degrees on the axis and 100 degrees at maximum shift - it also has a built-in filter set and a specially designed lens hood.

If you work with a (PC) lens or want to work with one, here are some special notes and suggestions:
⚪ If your camera has interchangeable screens, replace the original one with a screen that has a non-grained glass surface and grid lines.
These will help you make sure that the verticals are really vertical and the horizontals are really horizontal.
⚪ Remove the prismatic lens, if possible, and replace it with an ormagnifier viewer, like the one you see in Figure (8).
⚪ Follow a solid three-legged pillar, preferably with double levels on top of it. So you can make sure that the equipment is really vertical and horizontal.
⚪ Shortening can occur when shifting to extremes in one direction, so make test images in all directions and read the information sheet that comes with each lens.
⚪ The narrow expression is necessary, and you have to place the lens on the aperture for taking the picture and the expression for the scene, then open up the focus, and work manually by setting the lens to the pre-equipped aperture, then release the shutter.
We point out here that the Minolta lens is the only one that will set the aperture at the preset value.
⚪ For points far from the axis of the image, the lightening is less compared to the lightening of the points on the axis: this is true with wide-angle lenses in particular and it is known as the Cosina effect (Cosina effect). It is in the center of the film, so it will be underexposed, this is seldom noticeable. However, when shifting the direction of the lens, especially at the maximum shift locations, it may happen that one of the edges or corners of the film is noticeably underexposed, and an increase of half a stop on the normalized exposure will correct this phenomenon, especially if the concerned area is not very sensitive. Also, as with all wide-angle lenses, more sky light is included, and photos may need to correct for overexposed. Make some test photos, and keep careful records.

⚪ Using your (PC) lens on a blower or copier camera provides you with organizational, compositional and freedom methods that you do not have in any other way, especially if the lens has a tilt feature or (VFC).
This, and because of the specialized optical design and the current limited sales volume of conversion lenses, they are more expensive than traditional wide-angle lenses. Same focal lengths and apertures. However, if you are thinking of buying a wide-angle lens, and a 28mm lens in particular, think carefully about investing what you pay in buying a (PC) lens. You will thus get a wide angle lens that does much more for you.⏹
⏺ Table of specifications of (P.C) lenses of all types ⏹