Aperture is one of the main parameters that you need to pay attention to when choosing a lens. The optical intensity of the optical device shows the level of attenuation of the light flux.
In other words, this parameter shows whichpart of the light flux can pass through a lens system of this lens. The light flux when passing through the optical device is partially scattered and reflected from the lenses, partially absorbed by the materials from which the lenses are made (optical plastic, glass). As a result, it can significantly weaken at the expense of these physical characteristics.
However, this is not the only parameter determiningaperture, which you need to pay attention to when choosing a lens. The optical intensity of the optical device depends on the value of the maximum opening of the diaphragm. The more open the diaphragm, the more light enters the lens. And so the lens, the aperture of which makes f / 1.8 or 1: 1.8, is considered more luminous in comparison with the lens f / 2.8 or 1: 2.8. Often, for the sake of simplicity, the optical power of the optical device is determined by the level of the maximum open aperture that allows this lens to be exposed. However, the light-beam is an internal characteristic of the optical system's construction, and the value of the relative aperture opening performs only a part of the functions associated with determining the aperture of the device. Nevertheless, from a practical point of view, it is easier to compare lenses by such a parameter as the maximum possible value of an open aperture. So these two concepts can be considered identical.
The optical power of the optical system is always indicated intechnical characteristics of the description of the lens, as well as marking the body of the device near the front lens. For example, the lens speed of Canon 24-70 f / 2.8. It means that shooting with such a lens allows you to open the aperture to a maximum value of 2.8. This means that the device will not allow shooting with a diaphragm 2,0, 1,8, etc.
The lens, whose aperture allows you to shoot onthe value of the aperture level from f / 1.2 to f / 2.8, is considered luminous. Devices with a level from f / 3.5 to f / 6.3, do not belong to a high-aperture, they are usually called "dark", since they pass a small amount of light flux. Some leaders in the production of optical systems (for example, Leica and Carl Zeiss), produce models with a luminosity from f / 0.7 to f / 0.95. The most common luminous lenses among photographers are instruments with a value from f / 1.4 to f / 2.8.
Now consider what the parameter affectsaperture. All the advantages of such lenses are associated with the value of the aperture. This is because when shooting aperture affects the amount of light passed through the lens and the depth of field in the frame. Thus, the lens speed of a digital camera lens affects the ability to shoot under low light conditions. The more the aperture is opened, the less the depth of field of the frame will be obtained, that is, the objects that do not fall into the focusing zone will be blurred more.
