تأثير المرشحات الضوئية في الطبقة الحساسة .. كتاب الإضاءة والفلم

Effect of optical filters on the sensitive layer:

We started our discussion about optical filters by explaining the parts that they absorb from the white rays, and those that allow them to permeate, but we aim in this book to also know the results of using an optical filter for filming with a specific film, as we previously mentioned (on p. 119) that there is a difference between Eye sensitivity and sensitivity of films to spectrum rays. In order to know the effect of any light filter on a specific film, the following follows: The colors that the filter absorbs and the colors that the film does not perceive are subtracted from the sum of the colors of the rays that make up the white light.

Example 1:
What are the colors of the rays recorded by the panchromatic sensitive science when using a yellow filter?

the answer :

The colors that are recorded on the sensitive flag at that time are:
(white rays) - (rays absorbed by the yellow filter + rays that are not sensed by the film) = (red + green + blue) - (blue + .) = red + green.

That is, the panchromatic film with a yellow filter records only red and green rays. And if we seek accuracy in the answer, it is better to do the subtraction from the reality of the graphs, which are more accurate expressions of the characteristics of sensitive films and the characteristics of optical filters (Fig. 55).

Example 2:

What are the rays that Blue Sensitive Film records when using a yellow filter?

the solution :

The x-rays that are recorded are:

visible rays) - (the rays absorbed by the yellow filter + the rays that are not sensed by the film) = (blue + green + red) - (blue) + (green + red) = zero (0) meaning that if we use a yellow filter with a sensitive film For blue rays, learning is not affected at all.
This result is considered completely correct from the theoretical point of view, but from the practical point of view, the matter is different, as it is rare that we get a completely pure yellow filter (100%), and on the other hand, there is no film that is sensitive to blue rays only as understood from the meaning of this expression. Films are also sensitive to indigo rays, such as Indigo rays. Therefore, some blue and noble rays pass through the filter, which affects the film very weakly. If the exposure to light is increased, the effect of those rays on the film increases, and the density increases accordingly.