The Difraction In Photography

The Difraction In Photography

As can be seen, the Airy disk decreases with the increase of the opening. In particular, with f / 4, the size of the Airy disk is equal to 5.3 pM against a pixel size equal to 5.5 microns. Already from f / 5.6 the disc exceeds the size of the pixels becoming “appreciable” (7.5 mM vs 5.5 m). At the minimum aperture (f / 32) the size of the Airy disk are huge: 42.6 pM against the usual 5.5 mM of the pixel size. Consider also that in higher performance cameras, such as the D800, the pixel is smaller than (equal to 4.9 uM), for which the effect of diffraction begins to be important (although we speak of something almost invisible to the human eye) to values ??of f “technically” inferior to those relating to D5000 (obviously, in order to appreciate the defect with the naked eye, one must reach high values ??of f, from f / 16 onwards).

Thanks to the anti-aliasing filter (and to the Rayleigh criterion), an Airy disk may have a diameter of about 2-3 pixels before reaching the first diffraction limit resolution (assuming a perfect lens). However, precisely because the lenses are never perfect http://akusaraprosound.com, the diffraction already has a visual impact before reaching this diameter. For example, the Canon EOS 20D begins to show diffraction to about f / 11, while the Canon PowerShot G6 begins to show its effects only at f / 5.6. On the other hand, the Canon G6 does not require small openings such as 20D to obtain the same depth of field (due to the much smaller size of the sensor).

Because the size of the Airy disk also depends on the wavelength of light, each of the three primary colors will reach its diffraction limit in different openings. The classic digital SLR cameras are capable of capturing the light with a wavelength between 450 and 680 nm which results in an Airy disk whose diameter is at most 80% of what is shown in the drawings above , calculated at 550nm.

Another complication is that the sensors that use a Bayer matrix (so most) devote most of the pixels of the green color compared to the blue and the red (about twice). For the wavelengths, its green is the color that is affected by the first diffraction (blue is the last), for which in the photographs, the limit of the diffraction resolution, first of all we will notice a loss of resolution and brightness in green Colour.