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[1] [2] [3] The f-number is also known as the focal ratio, f-ratio, or f-stop, and it is key in determining the depth of field, diffraction, and exposure of a photograph. [4] The f-number is dimensionless and is usually expressed using a lower-case hooked f with the format f / N , where N is the f-number.
Popular exposure chart type, showing exposure values EV (red lines) as combinations of aperture and shutter speed values. The green lines are sample program lines, by which a digital camera automatically selects both the shutter speed and the aperture for given exposure value (brightness of light), when set to Program mode (P) .
The filter factor, given the exposure change in f-stops, may be calculated using the formula: 2 f s t o p = f i l t e r f a c t o r {\displaystyle 2^{fstop}=filterfactor} An example: A deep red filter with an f-stop change of 3 stops
The photography term "one f-stop" refers to a factor of √ 2 (approx. 1.41) change in f-number which corresponds to a √ 2 change in aperture diameter, which in turn corresponds to a factor of 2 change in light intensity (by a factor 2 change in the aperture area). Aperture priority is a semi-automatic shooting mode used in cameras.
For example, the photographer may prefer to make his sunny-16 shot at an aperture of f /5.6 (to obtain a shallow depth of field). As f /5.6 is 3 stops "faster" than f /16, with each stop meaning double the amount of light, a new shutter speed of (1/125)/(2·2·2) = 1/1000 s is needed. Once the photographer has determined the exposure, aperture ...
Sunlit subject shot on a digital camera set to ISO 100, exposed at f/8 at 1/400 second which is the same exposure value as f/16 for 1/100 second, the recommended "sunny 16" exposure. In photography, the sunny 16 rule (also known as the sunny f /16 rule) is a method of estimating correct daylight exposures without a light meter. Apart from the ...
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Therefore, each f-number factor of the square root of two (approximately 1.4) is also a stop, so lenses are typically marked in that progression: f / 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.. The ISO arithmetic speed has a useful property for photographers without the equipment for taking a metered light reading.