Visual example: aperture vs. Pixel size

The size of the airy disk itself is only useful in the context of depth of field and pixel size. The following interactive table shows the airy disk within a grid which is representative of the pixel size for several camera models (move your mouse over each to change grid).

	Aperture	Camera Type	Pixel Area
	f/2.0	Canon EOS 1D	136. µm^2
	f/2.8	Canon EOS 1Ds	77.6 µm^2
	f/4.0	Canon EOS 1DMkII / 5D	67.1 µm^2
	f/5.6	Nikon D70	61.1 µm^2
	f/8.0	Canon EOS 10D	54.6 µm^2
	f/11	Canon EOS 1DsMkII	52.0 µm^2
	f/16	Canon EOS 20D / 350D	41.2 µm^2
	f/22	Nikon D2X	30.9 µm^2
	f/32	Canon PowerShot G6	5.46 µm^2

Recall that a digital sensor utilizing a bayer array only captures one primary color at each pixel location, and then interpolates these colors to produce the final full color image. As a result of the sensor's anti-aliasing filter (and the Rayleigh criterion above), the airy disk can have a diameter of about 2-3 pixels before diffraction limits resolution (assuming an otherwise perfect lens, when viewed at 100% on-screen). However, diffraction will likely have a visual impact prior to reaching this diameter.

As two examples, the Canon EOS 20D begins to show diffraction at around f/11, whereas the Canon PowerShot G6 (compact camera) begins to show its effects at only about f/5.6. On the other hand, the Canon G6 does not require apertures as small as the 20D in order to achieve the same depth of field (for a given angle of view) due to its much smaller total sensor size (more on this later).

Since the size of the airy disk also depends on the wavelength of light, each of the three primary colors will reach its diffraction limit at a different aperture. The calculation above assumes light in the middle of the visible spectrum (~550 nm). Typical digital SLR cameras can capture light with a wavelength of anywhere from 450 to 680 nm, so at best the airy disk would have a diameter of 80% the size shown above (for pure blue light).

Another complication is that bayer arrays allocate twice the fraction of pixels to green as red or blue light. This means that as the diffraction limit is approached, the first signs will be a loss of resolution in green and pixel-level luminosity. Blue light requires the smallest apertures (highest f-stop) in order to reduce its resolution due to diffraction.

Technical Notes:

• The actual pixels in a camera's digital sensor do not actually occupy 100% of the sensor area, but instead have gaps in between. This calculation assumes that the microlenses are effective enough that this can be ignored.

• Nikon digital SLR cameras have pixels which are slightly rectangular, therefore resolution loss from diffraction may be greater in one direction. This effect should be visually negligible, and only noticeable with very precise measurement software.

• The above chart approximates the aperture as being circular, but in reality these are polygonal with 5-8 sides (a common approximation).

• One final note is that the calculation for pixel area assumes that the pixels extend all the way to the edge of each sensor, and that they all contribute to those seen in the final image. In reality, camera manufacturers leave some pixels unused around the edge of the sensor. Since not all manufacturers provide info on the number of used vs. unused pixels, only used pixels were considered when calculating the fraction of total sensor area. This pixel sizes above are thus slightly larger than is actually the case (by no more than 5% in the worst case scenario).