اصلاح منظور الصورة في اثناء عملية التكبير .. كتاب التحميض والطبع والتكبير

Fix the perspective of the image during the zoom process:

You may see in the negative image that the lines or ribs that were perpendicular to the ground or originally parallel in nature have appeared slanted or non-parallel in the image.
(Fig. 87 on page 279) This may not be a mistake on the part of the photographer, but rather something necessitated by the laws of photographic perspective.
Photographic Perspective

This defect can be overcome when enlarging the image if we follow one of the immediate methods: First: by tilting the illumination house with the magnifier (Fig. However, the increase in the tilt of the lighting house in the usual enlarging machines may result in another defect (known as Vignetting), as the metal frame surrounding the lens blocks part of the light rays passing through the negative images, so the light image (falling on the sensitive paper) is not completely complete. Therefore, it is better to follow one of the two methods shown later.

Second: It is also possible to fix the degree of inclination of the image lines by tilting the sensitive paper holder. The following are the action steps:

1- The negative is placed in its place with the magnifier and its lamp is lit.
2- The sensitive paper holder is lifted from the side from which the straight lines diverge, and it continues to be lifted gradually until the lines appear straight or parallel in the desired shape, then the height of this side is fixed (Fig. 77-b).

3- The distance should be set in the middle of the image, taking into account the narrowing of the aperture of the diaphragm of the magnifier lens so that it becomes possible to increase the depth of field to overcome the lack of sharpness of some parts of the image as a result of the difference between the distance between the lens and one end of the sensitive paper (which is the near end) from the distance between it and the other end. the distant other.

4- As it follows from placing the sensitive paper holder in an inclined manner that the side closest to the lens receives more illumination than the side farthest from it, so it is taken into account that the exposure of the side closest to the lens is less than the side farthest from it, and therefore the method of dodging is followed (p. 271) and several Initial experiments to determine the amount of increase in exposure that is suitable for the side farthest from the lens. Third: The perspective of the image can be fixed by using a camera with a swinging back (1) and a moving base for the standard lens, if the machine is prepared as a zooming device, by installing a light house on top of the ground glass, which is specially prepared for each type of these machines, then The machine is installed in a stand similar to the one used in photographic transfer work, Reproduction Stands, lest the heat of usual light sources affect the negative image or the body of the machine and damage it, so it is sometimes prepared with light sources that do not emit intense heat energy
(called cold light head). Or heat absorbent filters are placed. This method is distinguished from the others (discussed in the second item on page 314) in that there is no reason to narrow the aperture of the diaphragm, if we use an enlargement device of this type. And we show in the form of 79 an explanation for this.

The previous three methods are also used as means to fix the perspective of images that suffer from errors in their perspective. Also, the same methods may be used to deliberately distort the images as a method of photographic deception, and we will come back to explain this in a next chapter.