Aperture is one of the main parameters that you need to pay attention to when choosing a lens. The luminosity of the optical device shows the level of attenuation of the light flux.
In other words, this parameter shows how much of the light flux can pass through the lens system of this lens. The light flux 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 may be significantly weakened due to these physical characteristics.
However, this is not the only parameter that determines the aperture ratio, which you need to pay attention to when choosing a lens. The luminosity of an optical device depends on the value of the maximum open aperture of the aperture. The further the aperture is opened, the more light enters the lens. And so a lens whose aperture is f / 1.8 or 1: 1.8 is considered to be faster than an f / 2.8 or 1: 2.8 lens. Often, for the sake of simplicity, the luminosity of an optical device is determined by the levelmaximum aperture that allows you to set this lens. However, the luminosity is an internal characteristic of the design of the optical system, and the value of the relative aperture of the diaphragm performs only a part of the functions associated with determining the luminosity of the device. However, from a practical point of view, it is easier to compare lenses by such a parameter as the maximum possible aperture value. So these two concepts can be considered identical.
The aperture ratio of the optical system is always indicated in the technical characteristics of the description of the lens, and also marked on the body of the device near the front lens. For example, Canon lens aperture 24-70 f / 2.8. This means that shooting with such a lens allows you to open the aperture up to the maximum value of 2, 8. This means that the device will not allow shooting with aperture 2, 0, 1, 8, etc.
A lens whose aperture allows you to shoot at an aperture level of f/1.2 to f/2.8 is considered fast. Fixtures from f/3.5 to f/6.3 are not fast, they are usually called "dark" because they let in a small amount of light. Some of the leaders in the production of optical systems (for example, Leica and Carl Zeiss) produce models with aperture levels from f / 0.7 to f / 0.95. The most common fast lenses among photographers are devices with a value from f / 1.4 to f/2.8.
Now consider whatinfluences the luminosity parameter. All the advantages of such lenses are related to the aperture value. This is because when shooting, the aperture affects the amount of light that passes through the lens and the depth of field in the frame. Thus, the lens aperture of a digital camera affects the ability to shoot in low light. The more the aperture is opened, the less the depth of field of the frame will be, that is, objects that are not in the focus area will be more blurred.
