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I think you often heard such words as " lens aperture".
Let's figure out what it is. Aperture refers to how much light can pass through the lens and hit the camera matrix. The faster the aperture of the lens, the more opportunities when photographing in situations with poor lighting without using a tripod or flash.
The lens aperture depends on three parameters:
- focal length
- diaphragm
- optical quality
Maximum open diameter ratio diaphragm to the focal length is called aperture ratio (geometric aperture ratio of the lens). It is this aperture ratio of the optics that is indicated on the lenses, I think you have seen the signatures - 1: 1.4, 1: 2.8, 1: 5.6, etc. 1:3.5).
The fastest lens, was released for NASA in 1966 and was used for shooting dark side moon. It was called the Carl Zeiss Planar 50mm f/0.7 and had an aperture ratio of 1:0.7 and ten were made.
A portrait lens with a fixed focal length is one of the fastest lenses available. Fast fixes are relatively cheap, for example, when compared with a fast zoom lens.
The fast lens is ideal for portraits, they give a small depth of field which is important for portrait photography .
Which lens to choose, with aperture 1.2, 1.4 or 1.8?
Beginners usually want to buy a faster lens that costs a lot more. But do you have to pay for an f/1.4 aperture if you don't use it!?
Depth of field (abbreviated DOF) depends on how fast the lens is, so when shooting at f/1.2, f/1.4, or f/1.8, the focal plane is quite small and your subject may be out of focus.
The f/1.2 aperture should be used when there is not enough light, although this does not always solve the problem, it is easier to raise ISO especially if you have full frame camera. Sometimes, even at 50mm at f/2.8 a lot of detail can be out of focus, so it's best to play it safe and use at least f/3.2:
So
The fast lens is ideal for portrait photography.
Fast lenses for nikon and canon: what is lens aperture and f number?
Any lens is characterized by one or another aperture. This parameter is understood as the degree of attenuation by the lens of the light flux entering it. The aperture ratio is affected by the transparency of the lenses, the aperture diameter and some other characteristics of the optics. But if you come to an electronics store and ask the seller about the aperture ratio of a particular lens, you will get a strange answer. The person will just call you maximum value diaphragm. The fact is that in our age of widespread simplification, people begin to mean precisely the size of the aperture by aperture. This lesson will tell you just about the diaphragm. We will try to explain why this parameter needs to be adjusted when shooting and what it affects.
Lens aperture - f number
If you regularly read our lessons, you already know how the maximum aperture value is indicated in the characteristics. So the aperture ratio of the lens is the f number, and to be precise, then f divided by one or another number. After all, f stands for focal length. And the aperture value is the number by which the set focal length is divided.
Aperture must be indicated in the characteristics of any lens. This does not necessarily mean separately sold optics. These words apply even to compact cameras with a built-in lens. Moreover, now the parameter "Aperture" or "Aperture" can be found even in the characteristics of flagship smartphones. Indeed, in the production of cameras built into them, more and more advanced lenses are used. As a result, the device receives high-aperture optics, and the pictures become very bright. 
But enough words about the creation of optics. Let's approach lens aperture from the other side. Now we need to understand why buyers pay attention to this parameter at all. And everything turns out to be very simple. If the diaphragm is able to open very wide, then a lot of light enters the matrix. Some lenses provide f/1.4 aperture. With this parameter, you can use a shutter speed of 1/4000 second, while the matrix will have enough light.
Increased aperture favorably affects the quality of portrait photographs. The more the aperture opens, the smaller the zone of sharpness becomes. As a result, you can achieve beautiful blurred background. This effect is also called the word "bokeh". That is why experienced photographers use fast lenses to shoot portraits. They leave all kinds of zoom optics for shooting landscapes. 
Also glass with good number f are needed for evening photography. In low light, either a slow shutter speed or a wide aperture is required. Nobody will interfere with increasing the shutter speed, but this will not allow you to capture moving objects in the frame. Therefore, it is better to open the aperture to f / 1.8 or f / 1.4. But this method does not always work either. Indeed, with this value, the field of sharpness narrows, and sometimes this does not correspond to the photographer's idea.
Fast lens for Canon and Nikon
In stores, cameras with whale optics are sold in large quantities. And a rare buyer understands that the manufacturer puts a lens with an average, and sometimes even terrible aperture ratio, into the kit. This is especially true for optics with a wide range of focal lengths. Therefore, in various forums and specialized resources, people are recommended to purchase a “carcass”. This word refers to a kit in which there is only a camera. Well, then a fast lens is bought separately. As a result, it spends a little large sum than for a kit with whale optics, but the result will please you much more. 
Unfortunately, not every lens sold in the store is fast. Be sure to look in the specifications for the aperture value. At 50mm focal length, f/1.8 aperture will be considered fast. The higher the focal length, the smaller the maximum aperture opening. Think of the lenses used by photographers working on football matches. They would give anything for f/2. But it is still technically impossible to achieve it.
Let's take a look at some good fast lenses that you can find in stores these days. At the same time, we are now interested in inexpensive optics for cameras from the two most famous manufacturers - Canon and Nikon. 
Let's start with fast lenses for Canon, and here the Canon EF 50mm f1.8 II glass is very popular now. This is the second generation of this optics. As the name implies, the lens has a fixed 50mm focal length. This can be confusing for beginner photographers. But on the other hand, the aperture is able to open up to f / 1.8. Alas, the lens is not the best. Many buyers find fault with its body. But this should not be surprising, since nothing else can be expected from budget glass (you can buy it for 4,000 rubles).
More than four times more expensive is the Canon EF 50mm f1.4 USM. Sometimes even experienced professionals acquire such a lens. They note a very high aperture and beautiful bokeh obtained in the pictures. 
If we talk about fast lenses for Nikon, a lot of them have also been created, and mostly high value aperture is available for instances with a fixed focal length. For 5 thousand rubles, it is proposed to buy a Nikon 50mm f1.8D AF Nikkor. 
This optic delivers the popular 50mm focal length. It is great for cameras with a crop factor of 1.5. But there are also problems with the body, the lens is extremely flimsy.
Nikon 24-85mm f2.8-4D IF AF Zoom-Nikkor looks like a very interesting solution. This is a zoom lens. At the minimum zoom, the aperture can open up to an acceptable f / 2.8 value. But as the focal length increases, the aperture deteriorates. This is the problem with any inexpensive zoom lens. Although this decision cannot be called a budget one, more than 24 thousand rubles are asked for glass in Russian stores. 
Full-frame DSLR owners should be interested in the Nikon 24-70mm f2.8G ED AF-S Nikkor lens. This optic is similar to the previous one, only the range of focal lengths is slightly narrower. But the aperture here does not change when using the zoom! There are other improvements as well. But this lens costs a lot - 65 thousand rubles.
Results: lens aperture - what is it?
It's time to sum up our lesson: lens aperture - what is it and how to understand it correctly? If you are interested in the correct answer, then this is the degree of attenuation of the light flux passing through the lens. But most often the word "aperture" means the amount of aperture opening. 
High aperture is needed to get bright photos with high speed exposure. Also, a wide-open aperture is needed to maximize the blurring of the background, which makes for beautiful portraits. Lenses with a fixed focal length have good aperture. If you are interested in fast optics with the ability to zoom, then get ready to spend a lot of money. And the more zoom you are interested in, the more large sum required. This is due to the complexity of manufacturing such lenses. 
This concludes our lessons on the diaphragm. Visit our site regularly, then you will not miss the following lessons. In them, we will look at the camera in all details and find out which characteristics are the most important. 
03.12.2011 13380 reference Information 0
Lens aperture - a value that characterizes the degree of attenuation of the light flux by the lens. To understand what a fast lens is, let's understand how the lens affects the flow of light.
As you know, when photographing, light hits the matrix, forming an image. The lens attenuates the light output. This degree of attenuation is called aperture ratio.
In simple terms, aperture is the maximum amount of light that a lens can capture. Lens aperture refers to the maximum aperture (hole through which light enters the sensor). It is characterized by a minimum f-number. That is, the smaller the number, the more the aperture is open and more light enters. The minimum aperture value corresponds to the declared aperture. So, at f / 2 aperture, the aperture value can be from two or more.
If the lens is not a fixed lens (with a fixed focal length), then two pairs of numerical characteristics will be indicated on it: the first pair is the minimum and maximum possible focal lengths, the second is the variable aperture corresponding to these focal lengths (the first number is for the minimum, the second is for maximum). There are also more expensive lenses - having a fixed aperture with a variable focal length.
Why do photographers chase fast lenses?
There are many reasons. In a reflex camera, sighting is carried out through the shooting lens - and with relative apertures of 1 / 5.6-8 human eye already poorly captures the picture, that is, a fast lens is more comfortable for the photographer.
A fast lens can shoot at faster shutter speeds, which is vital when shooting sports and wildlife, because to stop the movement of the wings of a bird, you need shutter speeds faster than 1/1000 s. The longer the lens is, the more it needs short shutter speeds when shooting handheld, otherwise it is easy to “blur” the image.
A fast lens can shoot in more challenging lighting conditions, so indoor fashion, dance, and some sports photographers invest in very expensive telephoto lenses with apertures of f/2.8 and f/2 or more.
A fast lens can shoot at low sensitivity. In digital cameras, lower sensitivities and faster shutter speeds result in a more noise-free image.
An important factor for artistic photography- By changing the aperture value, you can change the depth of field. At full aperture, at apertures greater than f/2.8, the depth of field (DOF) is shallow, allowing the background, foreground, or unnecessary detail to be blurred. This quality is difficult to replace in portrait photography, and in general it is essential for almost any genre, except, perhaps, landscape. The portrait, by the way, does not like too bright light.
small depth of field
For telephoto lenses professional level aperture is also important because they are used as part of a photosystem with converters that increase the focal length. For example, a 300mm professional telephoto with a one and a half converter turns into a 450mm, and with a double converter it turns into a 600mm.
The luminosity also has one technical limitation. Autofocus systems work reliably at apertures up to f/5.6. At smaller ones - (f / 6.3, f / 6.8 - they usually work, but unreliably and less accurately, and at f / 8 or f / 11 they don’t work at all. But as the focal length increases to the root, the square of two aperture drops by one step. Accordingly, a telephoto lens with f / 4 aperture and a 2x converter will not work in autofocus mode, since the resulting aperture will be about f / 8, and the viewfinder will be visually darkened.
At the same time, the aperture also changes when focusing. For example, if the lens is focused on an object on a scale of half its natural size (1: 2), then its aperture ratio drops by one step, and if the natural size is taken, even by two. Thus, at the initial relative aperture of f / 4, autofocus will not be possible at all.
This is why photographers spend more money and wear heavier lenses, although they could use light and inexpensive zooms with exactly the same range of focal lengths.
