The aperture value is usually indicated both for interchangeable lenses for DSLRs and mirrorless cameras, and for standard optics - on board digital compact cameras, smartphones, action cameras and even video recorders. Understanding the principles of aperture designation (this is the same name for aperture ratio) will be useful for choosing the most suitable solution for the specific needs of the user.

Aperture and aperture - what is the communication?

The basis of photography is light - when shooting, it hits the matrix and thereby forms an image. But first, a beam of light is passed through the optical circuit of the lens, where it is inevitably weakened. The level of this attenuation is the aperture ratio. Aperture and aperture are related concepts. More precisely, it is the degree of opening of the aperture inside the lens that affects the aperture value. Also, light transmission depends on the antireflective coating of the lenses and the quality of their manufacture, but we will talk about this later.

The diaphragm in the lens design is a rotating rim consisting of individual “petals”. When rotated, the petals open or close. And the wider the aperture opening in the maximum open position, the higher the aperture ratio of the optics. However, there are still some pitfalls here.

This is what the aperture hole looks like close up.

At its core, a diaphragm is just a mechanism that reduces or increases the size of the hole through which light penetrates. And the maximum size of such a hole is limited by the design of the lens. Aperture is calculated by dividing the focal length of the optics by the size of the maximum open aperture (in millimeters). For example, for a conventional “fifty-kopeck” lens of 50 mm with an aperture opening of 25 mm, the aperture ratio will be 50: 25 = 2: 1

Such marks are quite rare on lens markings. Identical designations of aperture in the form of an F-number have become much more widespread. The lower the number indicating the aperture ratio, the higher it is. So, for the example considered, the aperture is written as f/2.0, F2.0 or F1:2.

The aperture of the optics varies depending on the degree of opening of the aperture.

Typically the aperture is at least f/1.0. But in exceptional cases, the maximum aperture ratio may be below “one”. This happens if the focal length of the lens is less than the size of the open aperture. With appropriate division, the result is less than f/1.0. Lenses with such a high aperture ratio are very rare and not a cheap pleasure. In addition, they are quite bulky and are not always equipped with autofocus systems (due to heavy lenses that are difficult to move). A good example of this is the super-fast Nikon Nikkor Z 58mm f/0.95 S Noct, weighing under 2 kg. Long-focal lenses are also rarely fast - it’s also not easy to make a huge aperture in them, based on the focal length.

The large and heavy super-fast Nikon Nikkor Z 58mm f/0.95 Z Noct lens will cost the same as a good used foreign car.
Good to know. The maximum open aperture of the aperture is more correctly called the relative aperture. After all, the diaphragm itself is just a mechanism that regulates the size of the hole to reduce or increase light transmission. There may not be such a mechanism in the lens - then it will always shoot at the widest aperture. The vast majority of smartphone cameras are designed this way.
Popular lenses with permanent aperture

Aperture stops

The difference between lenses with a conventional aperture of f/1.4 and f/4.0 lies in the degree of opening of the aperture and the amount of light transmitted. Note that the maximum aperture ratio of the optics is a standardized parameter. It is clearly shown on the scale:

Standard aperture range with exposure steps between adjacent values at 1EV.

The indicated values were chosen for a reason. Between each of them there is a difference of exactly one exposure stop (1EV). When switching the exposure by one stop, the flow of transmitted light changes by half. This is explained by banal mathematics - changing the area of the circle of the diaphragm opening by half leads to a decrease or increase in its size by about 1.4 times.

Taking a close look at the standardized scale, a reasonable question arises: where does the aperture like f/1.8 or f/3.5 come from? The fact is that there are intermediate values - in many modern lenses and cameras, the relative aperture opening is adjusted in increments of not one stop of exposure, but 1/3 of a stop. This allows you to more flexibly adjust shooting parameters to suit certain conditions.

Popular portrait lenses

Variable and permanent aperture

The aperture can be either permanent (unchanged) or variable. The first option is found in all fixed lenses and advanced zooms, the second - in inexpensive optics with variable zoom ratios. For example, in kit (standard) lenses, the maximum aperture often varies from f/3.5 – 4.0 at minimum zoom to f/5.6 – 6.3 at the telezoom position. This is explained by the specific structure of the optical design to minimize the cost of the lens.

Most often, “floating” aperture is found in inexpensive whale zoom lenses.

In the category of lenses with a fixed focal length, models with a maximum aperture of f/2 or less are considered fast. However, in practice, the difference between conventional “portrait cameras” with apertures f/1.8 and f/1.4 can be striking. The first value is an attribute of amateur optics, while f/1.4 or even f/1.2 aperture can be found in advanced professional lenses. They are a priori larger and more expensive, have a more advanced optical design, are armed with the fastest autofocus and are better protected from atmospheric influences. Despite the minimal difference in aperture, f/1.4 and f/1.2 optics, in principle, belong to a higher class. Lenses with such maximum apertures are produced exclusively for full-frame SLR and mirrorless cameras.

Among zoom lenses, f/2.8 models can be called fast - only a few optics with variable zoom ratios have a higher aperture. The same applies to the category of lenses for medium format.

Popular zoom lenses

Shooting in low light conditions, background blur and bokeh character

So, what does high aperture optics give? First, the more light allowed through the lens, the better it “sees” in low light conditions. As a result, when shooting in a dark room or at dusk outdoors, you will be able to transmit maximum light to the matrix to form the final image. From a practical point of view, this allows you to set a lower light sensitivity and get less “noisy” pictures. For example, when photographing with an f/1.4 lens, the ISO value can be set at 400 - 800 units, but a conventional “standard” lens with a maximum aperture of f/5.6 will need ISO 3200 for similar conditions.

More light means more reliable operation of the camera's autofocus system. And one more thing is the ability to operate with shorter shutter speeds to “freeze” fast movements in the frame or shoot handheld in poor ambient light conditions without the risk of blurring the picture.

By shooting at a wider aperture, you can set a lower ISO and get low-noise images.

A wide open aperture provides a shallow depth of field (DOF), so fast lenses are the best tool for effectively blurring the background. Shooting with a small depth of field visually separates the object in the foreground from the background, which is indispensable in the portrait genre of photography, when shooting subject matter and in other situations. However, the nature of bokeh rendering depends not only on the lens aperture, but also on the design of the diaphragm mechanism, namely on the number of its blades. The more there are, the more attractive the contours of objects in the blur zone look. In portrait optics, the aperture often consists of 9 or even 11 blades.

The wider the aperture opens, the more the background behind the subject is blurred.

It is important to understand that purchasing a fast lens is not a panacea for obtaining photographic masterpieces. Handling such optics requires certain skills from the photographer - when shooting with open apertures, it is necessary to focus accurately and be sure to take into account the depth of field. Part of the solution to such problems can be left to the automation of modern cameras, for example, pivotal on the autofocus function based on the model’s eyes. However, in general, you will still have to control the picture “by eye”.

How does aperture depend on the size of the matrix?

As mentioned a little above, optics with the highest aperture (f/1.4 or less) are produced entirely for full-frame cameras. For cameras with cropped matrices, such lenses are practically not available - after all, this is an amateur class of photographic equipment. But how will a fast full-frame lens behave on a cropped lens? A twofold situation arises here.

On the one hand, the aperture must be recalculated into an equivalent one due to the inevitable change in the depth of field. This is done using the formula Feq. = F x crop factor. Those. on a cropped lens, a conventional f/1.4 lens will have an aperture of about f/2.1. However, the above is true only for the degree of background blur - the size of the matrix does not affect the exposure of the frame, so the parameters of shutter speed, aperture and light sensitivity will remain unchanged for both the full frame and the crop.

Popular cameras with APS-C matrix

Aperture ratio in video lenses

Specialized lenses for video recording have more stringent requirements for light transmission. Their aperture ratio is usually marked with T-stops (from the English Transmission). This is a designation for effective aperture ratio, which takes into account the loss of light flux when transmitted through the optical design of the lens.

Lenses do not provide transmission of 100% of the light flux - its passage depends on the quality of the glass, the anti-reflective and antireflective coatings used. And some of the light is necessarily reflected from the surface of the lenses. All this is taken into account in the aperture T-stops. And although in practice the difference between the geometric F-aperture and the effective T-aperture is usually small and is on the order of 1/2 an exposure stop, all other things being equal, a lens with a higher effective aperture will produce a brighter image.

In the segments of film and video lenses, aperture ratio is usually marked with T-stops.

All cinema lenses are a priori marked with aperture T-stops, whereas for conventional optics you can find out the effective aperture in special sources. For example, on the authoritative resource DxOMark.

As a conclusion

High-aperture optics will come in handy in portrait photography, when photographing weddings, christenings, and reports. But for studio, landscape, interior and architectural photography, aperture ratio no longer plays such a decisive role. In pursuit of high aperture, it is important to maintain a balance, but in general, such lenses will help you create beautiful, creative photographs that will be a worthy addition to your portfolio.