قوة تغطية العدسة الملائمة لآلات التصوير ذات الظهر المتأرجح وقاعدة العدسة المتحركة .

Lens Coverage Suitable for Swing-Back Cameras with a Moving Lens Base:

It is clear from the foregoing that we are forced to increase the extension of the bellows on one side of the swinging back than on the other side when we want to exaggerate or fix the perspective or increase the depth of field. The image must go outside the boundaries of the area covered by the lens, if you have not taken sufficient care to choose a lens capable of facing the movements of the previously mentioned camera parts. For these reasons, the factories that produce cameras designed to fix the perspective have always chosen lenses that are able to cover an area larger than what is required by the scale of the used machine.

The effect of the camera body orientation and the lens base sliding left or right on the image perspective:

Situation A: It shows the camera in its normal position facing the right wing of the building, so the parallel horizontal sides appear in nature, also parallel and horizontal in the picture, and it is also seen in the picture that the ratio of the size of the right wing to that of the left is correct in a way that makes the perspective of the picture identical to the real perspective in the picture. nature.

Mode B: It shows the camera with its body turned towards the left side with the lens sliding towards the right side, so the horizontal ribs lost their parallelism in the image and bulge in the perspective of the right wing image, and all the horizontal ribs tended to converge at a point located on the left side of the image, and its elongation also increased The right wing, and at the same time the left wing is smaller than the right wing.

Mode C: It shows the camera with its body directed towards the right side, while the base of the lens slid to the left side, resulting in an increase in the magnitude of the image of the left wing and an exaggerated extension in its perspective relative to the right wing of the building, with the tendency of the horizontal ribs to converge in the same direction. The tilt of the camera (which is the right side in this case).

Situation D: It shows a regular camera (its lens base is non-slip). It is noted that the camera is not facing the middle of the building, but facing its left side. This resulted in the enormity of the left wing and a decrease in the length of the right wing.

Mode E: shows a machine: shooting in case D, with the camera body tilted to the right and the base of the lens tilted to the left. This increases the exaggeration in the perspective of the image very much if the lens is of a short focal length with a sliding lens base and is in the same apparent place, which results in a severe exaggeration between the perspective of both wings, so the left wing appears very large in relation to the right wing whose elongation is reduced and its size is relatively small.

We explain this in the following example:

According to the law of the chord, a lens with a focal length of 108 cm is considered an average focal length if it were on a camera measuring 6 x 9 cm. Distance from the lens = 10.8 cm as well. This also indicates that any image located within this circle will be sharp and equal in intensity of its illumination.

If it is assumed that a part of the image (such as area number 4 in the form of 150) goes outside the borders of this circle, then it is expected that the intensity of this part of the image will decrease and the intensity of its illumination will also decrease.

And where conditions often call for photographing with swing-back machines and a moving lens base, to move the lens right or left, or raise or lower it, which results in its axis being far from the middle of the image, so the image must go outside the borders of the circle covered by the lens (area No. 2, Figure 2). 150) and enter within the limits of a larger circle (which is the area number 5 in the shape of 150). Based on this, if we do not take into account the previous considerations, then the intensity and intensity of the illumination of those parts that go outside the limits of the circle covered by the lens must be reduced.

For the aforementioned reasons, the power of covering the lens that is suitable for the machine with the swinging back and the base of the moving lens must be much greater than what is required for any usual camera. According to the previous example, if the camera has a size of 6 x 9 cm and it has a moving lens base, then the lens coverage must be suitable for a camera whose image has a larger scale (such as 9 x 12), i.e. the diameter of the circle covered by the lens is 15, and thus we guarantee sharpness The image is equal to its luminous intensity if the base of the lens moves.