How to find out the pixel size of a matrix?
Why might a photographer need a pixel size? There are enough such situations. Knowing the pixel size can be useful for determining safe shutter speeds when shooting with handhelds, because the smaller the pixel, the more noticeable the camera shake appears in the pictures, and the shorter shutter speed may be needed to eliminate movement. Having no idea about the pixel size of the matrix of your camera, you can not seriously talk about the depth of field, since the allowable diameter of the scattering circle directly depends on the size of the pixel. The value of the diffraction-limited aperture for a particular camera also depends on the pixel size. Finally, it is possible that when comparing multiple cameras, you will want to find out which one has a higher pixel density, which means it provides better detail and is more suitable for shooting distant objects.
The instructions for digital cameras very rarely indicate the pixel size of the matrix, but, fortunately, this parameter is quite easy to calculate on your own.
In most instructions, you can find information about the physical size of the photomatrix, as well as its linear resolution, i.e. about the number of pixels that fit on the matrix in the same row horizontally or vertically. For example, the matrix of a Canon EOS 70D digital camera has dimensions of 22.5 × 15 mm or 5472 × 3648 pixels. To find the size of one pixel, it’s enough to take the numbers for either side, divide the millimeters into pixels and multiply the quotient by 1000 to convert the result to micrometers (microns). We get the formula:
Formula 1, where
n is the pixel size in micrometers;
x is the linear size of the matrix in millimeters on one side;
a is the number of pixels on the corresponding side.
For the above 70D, the calculation will be as follows:
22.5 ÷ 5472 · 1000 ≈ 4.1 μm
The result is rounded to 0.1 μm. This is more than enough for any practical purpose. I used the long side of the matrix, but you can take the short side and make sure that the result is identical. All massive modern cameras have conditionally square pixels, and therefore, calculations can be done on either side of the matrix. However, when using the long side, the calculation error is somewhat less.
Perhaps you do not want to go into the instructions? Well, the pixel size can be calculated without knowing the exact size of the matrix.
You just need to remember the resolution of your camera in megapixels and its crop factor. Any amateur photographer knows these parameters of his device. The formula will look like this:
Formula 2, where
n is the same pixel size in micrometers;
Kf– crop factor;
N – resolution in megapixels.
Thus, for the Canon EOS 70D, which has a crop factor of 1.6 and a resolution of 20 megapixels, we get:
29.4 ÷ (1.6 · √20) ≈ 4.1 μm
As you can see, both formulas give an absolutely unanimous answer. You have the right to use the one you like best.
In case one of my readers is at odds with square roots, I decided it was my duty to independently calculate the pixel sizes for some of the most used digital formats and bring these data into a single table. Use on health.
Pixel size depending on the resolution of the camera and its crop factor, microns.
1 * 1.5 1.6 2 2.7
10 6.2 5.8 3.4
12 8.5 5.7 5.3 4.2
14 5.2 2.9
16 7.3 4.9 3.7
18 6.9 4.3 2.6
20 6.6 4.1 2.4
21 6.6 4.2
24 6 4 3.8
* Crop factor equal to one corresponds to
full frame (36 × 24 mm).
Obviously, the smaller the matrix of the digital camera and the higher its resolution, the smaller the unit pixel of the matrix. Is this good or bad?
The main, and perhaps the only positive consequence of reducing the size of a single pixel is an increase in the total density of pixels. The matrix with a higher pixel density, ceteris paribus, is able to provide better image detail. However, this advantage, although quite significant, draws a whole heap of negative consequences. High-resolution cameras are very demanding on the quality of the lenses and the technical skill of the photographer. They do not forgive negligence in work and with cynical pleasure capture in the picture not only useful details, but also all kinds of defects in optics, movement and focusing errors. The finer the pixel, the sooner the negative effect of diffraction on sharpness becomes noticeable when the lens is apertured. At the same time, a small pixel dictates a proportionally small size of the allowable scattering circle, thereby reducing the depth of the sharply depicted space.