مصدر الضوء .. كتاب التصوير الملون ، الكاتب عبد الفتاح رياض

Light source: The light source must emit equal light energy distributed in a very fair distribution over all the negative space, and the lamp house must be airtight so that it does not emit light. sensitive paper. On the other hand, work must be done to ventilate the lighting house for fear of the temperature rising too much. would fall on

The light source may be of the type of transparent tungsten lamps, or of the type of opaque white opal glass, and the validity of this or that type depends on the type of magnifier and whether it works with ground glass or an optical condenser, or both, and a 160-watt lamp of the usual types is sufficient. to enlarge.

And it is obligatory that the lamp be lit before the start of work for a period of time that may reach an hour if the lamp is new and has not worked before, because the new lamps are liable to noticeably change their color temperature in the first hours of their operation, then the color temperature of the rays begins to stabilize ( approximately) thereafter.

This has already been mentioned in our previous book Developing, Printing and Enlarging (1) that it follows from the use of diffusing glass in a device

Enlarging or using white, opaque opal lamps - when printing or enlarging - to reduce the degree of contrast in positive images (black and white, ,

This is the phenomenon known as the "Callier effect", however, deficiency

(1) Development, printing and enlargement (by the author (p. 248, first edition. Publisher: The Anglo Egyptian Bookshop - 165 Muhammad Farid Street, Cairo.
(fig. 67)

A magnifier prepared for color imaging, with a light housing that holds buttons to control the color of the rays.

The light rays come out of the lamp (No. (1) and are collected by the mirror (No. 2) and condensed on the other side of the mirror, until they fall on a flat mirror (No. 4) placed at an angle of 45 degrees so that the rays reflect on it in a direction of 90 degrees with respect to its first path). The rays pass through a fixed aperture (No. 7). Next to this slot there are three filters (No. 6) of yellow, crimson and cyan colors that can advance towards the fixed slot (No. 7) or move away from it as desired. And based on how close the filters are to the path of the rays leaving the aperture or far from it, the color of the rays that reach the diffuser glass (No. 8) located above the condenser (No. 9) can be controlled. The negatives (No. 10) are placed below the lower lens of the condenser. The number 11 indicates the magnifying glass, and the number 12 indicates the location of the sensitive paper.


In the left figure, number 13 refers to three Knobs buttons that can be rotated to control the extent to which the three filters (No. 6) slide towards the beam path or away from it.

jack. H. Coote, color Prints Revised edition 1963. P. 173
. The degree of contrast when using this type of glass or lamps may not be noticeable in the case of color photography, because the three pigments (inherent in colored negative or positive images) do not cause scattering of rays except to a very small extent, so that it can be neglected (1). Contrary to the foregoing, it is certain that traces of scratches (in color negatives) are clearly visible in color positive images.

R. Lamps known as “cold cathode lamps” may also be used as a source of illumination, assuming that they have been specially prepared for this purpose, and that their rays do not suffer from a decrease in redness, which, if it had happened, would necessitate the use of dense color-correcting filters to compensate for this deficiency. Boringly overexposure.

And if the color temperature of the rays emitted by the light source is severely affected simply by the increase or decrease of the voltage difference, then it is necessary in the operations of enlarging the color images that the light source connects to an automatic device to stabilize the electrical voltage difference (usually known by many names (Voltage Stabilizer Stabilizer Volt J).

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There is a simple method that may be practically feasible to stabilize the voltage difference during work (2), by working to reduce the electrical potential difference. Which feeds the lamp by an amount ranging between 5-100% of what is suitable for the lamp, and a variable resistance is used for that. The validity of the lamp to work is prolonged by following this method. .-

Jack H Coote, Color Prints, p. 192, 1st Revised Edition (1) 1963.

(r) b) Jack Conte, Color Prints, 1st, Revised. P. 163 A) Gevacolor, Principles of Making Prints, Treatment, P. 33- In the following two references, it is recommended to follow this method. This last reference also states that Rayco's Voltage Control works on this theory.