b. Either method of adjusting exposure for filter factor is acceptable. Under some
circumstances you may want to change the shutter speed in order to maintain the same aperture for depth
of field purposes. At other times you may want to change the aperture to maintain a fast shutter speed.
You as a photographer must choose the method most suitable for the job at hand.
3.
Types of filters.
a. Filters are constructed in three ways. These three types of filters are gelatin, cemented, and
glass. Dyed gelatin sheets come in a wide range of colors and density and can be cut to any desired
shape. However, they are very thin, unstable, and easily damaged. Cemented filters are sheets of gelatin
glued between two pieces of clear glass. This gives the filter some strength and stability, but the cement,
which must be optically pure, is sensitive to heat. Dyed glass filters are constructed in one piece; they
are not sensitive to heat as with cemented filters. There are fewer varieties of dyed glass filters than the
others mentioned. Both cemented and dyed glass filters affect the focusing slightly by displacing the
focusing plane, due to their thinner construction. However, dyed glass filters affect focusing to a lesser
degree.
b. Dirt, moisture, and fingerprints reduce the usefulness of all filters, so treat filters carefully.
Table 1-5 describes the characteristics of various filters, and Table 1-6 tells which filter to select for a
given situation.
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