(1) You can increase the exposure by using a wider aperture; opening one f/stop doubles the
exposure. All f/stop numbers get smaller as the aperture gets larger. If the basic exposure is f/5.6 and
the filter factor is 2, you must multiply by 2 or double the exposure by opening up one f/stop to f/4. If
the factor is 4, you must multiply the exposure by 4 or open up two f/stops. The term open up means to
enlarge the size of an aperture. A basic exposure using f/16 and a filter factor of 4 requires opening the
aperture to f/8 or two f/stops. If the factor is 8 you must open the aperture by 3 f/stops.
(2) Remember, the larger the f/number the smaller the aperture and the smaller the f/number,
the larger the aperture (fig 1-6a). Also remember that each f/stop allows 2x or 1/2 as much light to pass
through to the film as the next aperture; the same holds true with the shutter speeds. That means that
f/11 will pass 1/2 less light as f/8 and f/4 allows 4x more light to pass than f/8. Table 1-4 shows the
proper f/stops to use for various basic exposures and filter factors.
Figure 1-6a. F/stop relationship
Table 1-4. F/stops for filter factors