ضبط المسافة .. كتاب التحميض والطبع والتكبير

Adjust the distance:

As a result of changing the distance between the sensitive paper and the lens, it is necessary to adapt the distance between the lens and the negative image as well, to suit the previous dimension, and this is what has been termed as focusing. The theory of adjusting the distance in the enlargement device is not different from its theory in photocopiers, as it is a process that aims to adjust the distance between the lens and the negative image in a way that suits the distance between the lens and the optical image that is required to be recorded on sensitive paper, in order for the image to be sharp, and more. The distance between them, the lower the magnification ratio, and vice versa (Fig. 72).

The distance may be set manually by moving the lens up or down if the magnifier is vertical or back and forth if the magnifier is horizontal. Some practical difficulties may arise when adjusting the distance, if the negative image is very dense, or if it is not completely sharp, and then This negative image shall be replaced by an existing (neglected) one after scratching it several times with thin scratches (with a pin). After verifying that the distance has been set completely, this discarded negative is replaced with the original negative.

The distance is also set mechanically, by a non-manual Auto Focus Enlargers method in some types of the most expensive enlargers. In these types, the distance from the negative image is adjusted automatically, linked to the process of lowering the main group that carries the light housing, the lens, and the negative holder (Fig. 73). And when using a magnifier in which the distance is set automatically, and with the desire to place the sensitive plate upside down in the opposite of the correct position, that is, if we want to make the sensitive surface of the negative image not facing the sensitive surface of the positive materials, but rather facing the light source in the enlarger, it is noted that the device must be re-adjusted. Magnification taking into account the thickness of the sensitive glass that would raise the image level from the focal plane of the lens Focal Plane and the magnifier with automatic adjustment is usually adjusted assuming that the sensitive gelatinous surface will be directed down towards the surface of the wave material and it is preferable to use negative glass sensitive plates when you want to show the effect of the optical halo The thickness of the glass support reflected from the back surface of the glass helps to show this effect.

Putting the negative image in the magnifier:

The negative image is placed in the magnifier in a specially modified part known as the “Negative Holder”.

It is required that the distance of the negative image from the lens be slightly more than its focal length and less than twice the focal length, in order for a true enlarged image to be formed.

The sensitive surface of the negative image, whether when printing the image or enlarging it, should be facing towards the lens, i.e. facing the sensitive surface of the paper on which the image will be enlarged.

The sensitive surface in the negative is the least glossy, while in glossy or semi-matt papers, it is the most brilliant. It is easy to identify it in matte papers, if we know that the sensitive papers - whether they are glossy or matte - tend to curve slightly towards the sensitive surface.

As a result of the error in placing the negative image in the previous form, whether during printing or enlarging, the positive image comes out inverted, i.e. those visuals that were originally in nature appear on the left side on its right side, and this is what is called a mirror image (figure page 325). ).