Quality differences of photosensitive materials.
next question, which we are therefore interested in, Is, how well-exposed photos developed on both types of film appear as positives in the result. In transparencies obtained by the reversible method, as generally known, the color quality is almost perfect and cannot be improved.
If the picture is not satisfactory yet, the cause is not the method, but random errors, that occur or have occurred at the time the photos were taken, calling, and in some cases even in the photosensitive material itself. Comparing the slides copied from the negative with the slides obtained by the reversible method, we can conclude, that the first ones also show full colors, perfect and juicy, so that only a direct comparison of the same motifs and shot details can identify both materials. Understandable, that as a result of copying in three layers of positive material, there were practically losses in drawing and image details, which is unavoidable. When using negative material, some compensation is provided by the ability to make copies and a wider range of usable exposures of the material. An impoverishment of the richness of shades, which we can observe on the print obtained on paper, compared to a transparency obtained in black and white, also occurs in color photography. In most cases, especially in portraits, however, it does not play a major role, because on paper prints you can get very juicy colors by using masking. In some cases, such an image may even be unpleasant to the eye. We can then say, that it looks like a "kitsch postcard". There are such big differences between a transparency and a color print on paper, that we cannot compare them well and evaluate their advantages and disadvantages. The light sensitivity of color photo materials is indicated on the packaging. Pay attention to this, that we cannot say exactly “the color film has a light-sensitivity of 17°DIN”. We should just say “color film should be exposed as black and white material with a light sensitivity of 17 ° DIN”. DIN standard 4512 because specifying the method of measuring photosensitivity does not apply to colored materials.
In doubtful cases, when we do not have a light meter or its sensitivity is insufficient, we can take test photos on known black and white material and after development, comparing possible differences in photosensitivity, based on these results, determine the correct exposure of the colored material.
However, when doing reversible take off objects with very little contrast, for example, for medical images of skin surfaces or body openings, we can easily get confused. In these cases, we should expose the reversible material much longer than the color negative material, because the range of useful exposures of the latter is greater and with the exposure time insufficient for reversible films, it allows you to get good photos on negative material. We will return to this issue later when discussing exposure measurements.