التعارض بين حالتى استخدام الظهر المتأرجح لزيادة عمق الميـدان و استخدامه ٢-a.

The effect of the camera orientation and the sliding of the lens base together in the perspective of the image:

We went back before that placing the camera facing the middle of the parallelogram body (when the optical axis of the lens is perpendicular to the plane of the body, and the plane of the film is parallel to the plane of the body as well) is a position that guarantees maintaining the parallelism of the horizontal lines in the image, as we also learned that it is possible by The swinging back is to obtain frontal images of the bodies despite the lateral position of the camera, as shown in (Figures 143, 144, 145, 147, 148), and thus the horizontal parallel sides in nature remain parallel in the image as well.

It is not always desirable to keep the parallel horizontal sides parallel. Rather, it is my ability for the photographer to deliberately exaggerate the perspective of the image for the purpose of himself engineering facilities to show their enormity or to photograph to advertise commercial goods with exaggeration in the perspective of the image.

Here we add to the foregoing that although the camera is facing the middle of the body, it is also possible to exaggerate the perspective of the image by tilting the axis of the camera itself (not just the axis of the lens) to the right or left (cases b, c, d, e fig. 149) and it follows that Any of these conditions results can be summarized as follows:

(a) That the horizontal sides that are parallel in nature appear to be not parallel in the photograph, and that the point of convergence of these sides is located in the same direction towards which the camera is directed. If the machine is directed to erase the left side with the lens sliding towards the opposite (right) side, the height of the vertical ribs on the left side will decrease relative to the height of the ribs located on the right side as a result of the tendency of the parallel horizontal lines to converge on the left side (case B Figure 149).

Conversely, directing the camera towards the right side with the lens sliding towards the opposite (left) side results in a decrease in the length of the vertical sides located on the right side, so that they become relatively shorter than the length of those located on the left side of the image, in other words, the horizontal sides tend to The convergence at a point located on the right side (C, D, E of Figure 149)

It is also possible to exaggerate the perspective in the previous form by using any usual camera (the base of its lens is not moving) or changing the position of the middle of the building (as if it were facing the left side, for example, and not the middle completely).

However, there is no doubt that if a machine with a sliding lens base was used and in the same place as the camera shown in the previous case, it would be possible to exaggerate the perspective to a very large extent (please compare the two cases D and E in Figure 149).

In addition to the effect of the direction of the camera and the sliding of the base of the lens in exaggerating the perspective of the image, it can be said that this exaggeration in perspective can be increased to a large extent for the forest whenever the focal length of the lens decreases, and thus we see that lenses with a short focal length or obtuse angle are ideal for performing The maximum degree of exaggeration in the perspective if cooperated with other previous factors.