Figure 1-6. Absorption curves
Learning Event 2:
FILTER FACTORS AND TYPES OF FILTERS
1.
Filter factor determines exposure increases.
a. The filter factor compensates for less light reaching the film. Exposures must be increased
when using filters. The factor depends on the color sensitivity of the film, the color of the illumination,
and the density of the filter. Panchromatic (pan) film is sensitive to blue, green, and red light radiations.
Orthochromatic (ortho) film is sensitive to blue and green light radiations.
b. The more dense the filter, the larger the filter factor. Less light striking the film requires a
longer exposure.
c. The less sensitive the film is to the color of the filter, the higher the filter factor. Let us see
why. The color of the filter is the color that reaches the film. If the film is not very sensitive to that
color, you'll need a very long exposure. An extreme example would be to use a red filter with ortho
film. Ortho film is not sensitive to red light and a red filter passes only red light. So when red light
reaches the film it does not record. So do not use a red filter with ortho film.
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