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Assuming that the color image's enlargement ratio must be adjusted, it is certain that the matter calls for adjusting each of the exposure time or the aperture of the lens. Let us give an example for this in the case of enlarging a color image to a size of 9 x 12 cm, and the exposure time was 6 seconds with a diaphragm aperture of 208 (in the magnifier lens) and with a total correction of (40 - (2), then we wanted to make another image whose enlargement ratio is greater than Advance to 18 x 24 cm, for example (that is, the image area will increase by four times from the previous one), and here it comes to mind that the exposure should be increased four times, so the exposure becomes according to any of the following groups:

What should be done if we want to adjust the magnification of the color image?

28 with 24 seconds, 6 with 4 seconds, or 4 with 506 with 12 seconds

Although the previous estimates are completely correct from the theoretical arithmetic point of view, the matter differs slightly from the practical point of view, as a new factor known in photochemistry as “Failure of Reciprocity Law” and sometimes known as its discoverer D Schwarzschild reciprocity failure interferes.

== And this law states that “it is not necessary for the sensitive layer to be affected identically in the case of a decrease in the exposure time and an increase in the intensity of light, with the case of an increase in the exposure time and a relative decrease in the intensity of the light.” Accordingly, it is not expected that the effect on the sensitive layer will be equal in the case of using the three groups shown above, but rather it needs to be slightly modified (1).