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Diagram of decreasing apertures, that is, increasing f-numbers, in one-stop increments; each aperture has half the light-gathering area of the previous one.. An f-number is a measure of the light-gathering ability of an optical system such as a camera lens.
The cone of the focused light at the image plane is set by the size of the entrance pupil and the focal length of the lens. This is often referred to as the f-stop or f-number of the lens. f/# = f/D where D is the diameter of the entrance pupil.
N is the f-number; and; t is the exposure time ("shutter speed") in seconds [2] The second line is just applying the quotient identity of logarithms to the first line. EV 0 corresponds to an exposure time of 1 s and an aperture of f /1.0. If the EV is known, it can be used to select combinations of exposure time and f-number, as shown in Table 1.
Increasing f-stop decreases the aperture of a lens. In photography, stopping down refers to increasing the numerical f-stop number (for example, going from f / 2 to f / 4), which decreases the size (diameter) of the aperture of a lens, resulting in reducing the amount of light entering the iris of a lens. [1] [2]: 112
An example: A deep red filter with an f-stop change of 3 stops = A change of 3 f-stops is equivalent to a filter factor of 8. As a consequence of this relationship, filter factors should be multiplied together when such filters are stacked, as opposed to stop adjustments, which should be added together.
Preferred numbers represent preferences of simple numbers (such as 1, 2, and 5) multiplied by the powers of a convenient basis, usually 10. [ 1 ] Comparison of preferred numbers of the 1-2-5, Renard and f-stop series on a logarithmic scale divided into 40 equal intervals (blue)
As typical f-numbers for lenses for cell phones and DSLR are in the same range f /1.5–2 it is interesting to compare performance of cameras with small and big sensors. A good cell phone camera with typical pixel size 1.1 μm (Samsung A8) would have about 3 times worse SNR due to shot noise than a 3.7 μm pixel interchangeable lens camera ...
for a given maximum acceptable circle of confusion c, focal length f, f-number N, and distance to subject u. [ 3 ] [ 4 ] As distance or the size of the acceptable circle of confusion increases, the depth of field increases; however, increasing the size of the aperture (i.e., reducing f-number ) or increasing the focal length reduces the depth ...