وجوب زيادة التعريض عند إضافة المرشحات .. كتاب التصوير الملون ، الكاتب عبد الفتاح رياض

Exposure must be increased when adding filters:

The optical filter - as we know - absorbs a side of the light rays that pass through it, so it is obvious - according to general rules - that it is necessary to increase the exposure by an amount commensurate with the degree of density of the filter. This is the increase known in the science of photography as the “filter factor”, and this increase becomes necessary when printing and enlarging color images if we add any of the scarlet and cyan filters, but in the case of adding yellow filters, even if they actually absorb part of the radiation that It falls on them, but the factors of these filters are usually so small that we often bypass them

Although there are filter factories that recommend neglecting the filter agent if it is yellow, there are other factories that recommend neglecting it only if it is yellow of little intensity and it is necessary to increase the exposure by a small amount if it is very dense.

In general, when using filters produced by a particular factory, it is necessary to refer to the tables published by this factory to know the factors of the filters specific to its production. This is considered very vital, as the result of an error in the estimation of the filters factors is to increase or decrease the exposure to the appropriate limit when printing or enlarging color images, and it is not hidden from us that the colors of the image must be affected by the other as a result of the error in the exposure. Hey

On the next page, we give an example of a table of Magenta and Cyan filters produced by Agfa Gephart factories. Agla Gevaert