عوامل مرشحات تصحيح الألوان التي تنتجها مصانع أجفا .. كتاب التصوير الملون

Application examples for calculating the correct exposure time after adding new filters to fix the colors of positive images or deleting part of the filters:

Example 1: In the case of adding new filters: Assuming that the initial image was enlarged with the use of optical filters of (30) 20 (-) and was exposed for a period of 8 seconds, but it was revealed from its examination that it is possible to fix the colors of the image if we added to the previous filters 10-40 ), then what is the appropriate new exposure after adding these filters, another value of (40

Solution: The sum of the intensity of the new filters = 40 + 10 = 50. Referring to the filters factor table on the previous page, we find that increasing the intensity by (50) requires increasing the exposure by 1.6.. The new exposure = X 16 = 12.8 seconds. The viewer is that in cases of color enlargement, it is necessary to increase the exposure during printing or enlargement by parts of a second, which necessitates the use of an automatic watch attached to the printing or enlargement devices so that it allows adjusting the exposure to parts of a second. Note: It is too much

Example 2: The case of deleting part of the previously used filters: Assuming that the primary image was enlarged with the use of optical filters of (40 by 60) and obtained an exposure of 5 seconds, but it appears to us by examining its colors after showing that its correction has increased in error. Which necessitates that the group of previously used filters be reduced to (10 20 - 20). What is the new exposure period after reducing the density of the filters?
- 7. · = Solution: The value of the density of the filters in the new first image D D = - 2010 The total value of the reduction =

70 = 40 + 30 = sum of the value of the reduced filters density

2 = Factor of reduced filters (from the table on p. 319) The amount of exposure loss after lowering the filters E seconds = 25 seconds ... New exposure - 25 = 25 seconds -

We have to consider the effect of the rays absorbed by the optical filter glass in estimating the duration of the exposure: Before many of the optical filters that we use in color correction processes by deletion, they are compressed and fixed between two sheets of glass, and it is certain that the glass (whatever type) causes loss A side) may be 4% of the light rays falling on it, so if we know that placing filters in the path of the rays emitted by the magnifier (to correct the colors of the image) is what causes the rays to pass through four layers of glass, we will find that some of the rays falling on the filters It must be lost (by absorption or reflection).

The presence of glass layers in the path of the light rays will not cause any problems of value if we enlarge all the images with two filters, for example, in the filter drawer of the magnifier, as the percentage of lost rays remains constant at all times of enlarging the image, except that if it is necessary to use one filter In one of the batches, then it was necessary (for the sake of correcting the colors of the image) to enlarge the same image a second time with the use of two filters, then it is certain that the exposure will be affected and increase slightly to compensate for the decrease that results from the loss of a side of the light rays that passed through the two layers of the second filter glass.
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To simplify things. In order to facilitate the overcoming of the problem of exposure difference resulting from changing the number of filters when correcting images, it is possible to always keep a fixed number of transparent glass plates in the filter holder tray each time we enlarge a color image.

Here we may ask: What should we do if the image correction did not necessitate the use of only one filter? (i.e. only two layers of glass). In response to that, we say that the factories that produce the optical filters needed for printing and enlarging images have taken precautions, and always count within the set of filters prepared for this purpose a number of glass panels equal in size and shape to the shape of the glass panels between which the optical filters are pressed, for the photographer to use in addition to them. To the single candidate (with two layers of glass) to complete the agreed number. Thus, we see that in this easy and simple way, the photographer will have no choice but to calculate the amount of increase or decrease in exposure except that he must calculate the factors of filters only without paying any attention to calculating the amount of increase or decrease resulting from a number). Plates of glass between which filters are pressed (1).

(1) The number of optical filters needed to correct the colors of images varies greatly, and their duration may be one at times, and it is rare for them to increase to a year of filters at once, and we give the following examples:

number of filters

Like the case of wanting to be corrected

Filter icons

20 yellow 35 cyan, 55 yellow 125 magenta, 55 yellow 115 cyan, 125 yellow

20 yellow, 40 purple, 25 yellow, 30 purple