Open and closed aperture. What is aperture, shutter speed and ISO

Aperture (aperture) - the relative opening of the lens, which allows you to adjust the flow of light entering the matrix of a digital camera and control the depth of the field of view.

2. Aperture blades

The diaphragm is made up of thin metal blades that cover or open the light opening. There may be more or less depending on the lens model. The number of petals determines the shape of the diaphragm opening - it can be close to a circle, or have the shape of a hexagon. The more petals, the rounder the hole, and the more beautiful the pattern on the lens. For example, when shooting on a lens with a large number of petals, even round spots are formed in the out-of-focus zone, rather than geometric shapes resembling nuts. Modern lenses have rounded blades, despite their small number, provide soft and beautiful background blur.

3. F-number, steps, aperture values

Aperture number is the ratio of the focal length of the lens to the diameter of the aperture, denoted as f / x, where x is its numerical value. The diaphragm controls the flow of light entering the photosensitive elements of the matrix. The larger the f-number, the smaller the aperture, and vice versa, the smaller the f-number, the larger the aperture, respectively, more light passes through. For clarity: f / 16 - closed aperture, f / 1.4 - open.

Aperture values ​​are measured in stops.

1.0

1.4

2

2.8

4

5.6

8

11

16

22

Each stage differs from the previous one by 1.4 times, while the amount of light entering the camera matrix changes twice. For more accurate exposure in modern cameras, there are intermediate aperture values ​​\u200b\u200bthat are equal to 1/3 stops:

1.0	1.1	1.2	1.4	1.6	1.8	2	2.2	2.5	2.8	3.2	3.5	4	4.5	5
5.6	6.3	7.1	8	9	10	11	13	14	16	18	20	22	25	29	32

4. Depth of field

Depth of field (DOF) is the area in which the subject will be depicted sharply, and everything that goes beyond it is blurry.

The depth of field depends on the following parameters:

• diaphragm- the smaller the aperture value (open aperture), the smaller the depth of field; at a closed aperture, the depth of field will be throughout the entire depth of the frame;
• lens focal length- the smaller the focal length of the lens (for example, wide-angle), the greater the depth of field; on long lenses, the depth of field is noticeably reduced;
• subject distance- the smaller the distance from the camera to the subject, the less depth of field, the greater the distance, the greater the depth of field.

Influence of the diaphragm on the depth of field.

As you can see from the pictures, a larger aperture gives a more blurred background.

5. The formula for calculating the depth of field

R1 - the front boundary of the sharply depicted space; R2 - rear boundary of the sharply depicted space; R is the distance in meters at which focusing is performed; f is the focal length of the lens (absolute, not equivalent), the value in meters is substituted into the formula; K is the denominator of the relative aperture of the lens (aperture number); z is the diameter of the allowable circle of confusion, for negatives with a format of 24x36 mm equal to 0.03-0.05 mm (the value in meters is substituted into the formula).

6. Aperture control

The primary role of the diaphragm is to control the depth of field. The aperture value is set depending on the goal. For example, when shooting landscapes, when the sharpness should be across the entire field of the frame, the optimal aperture value will be f / 11 - f / 16, when shooting a portrait, where it is necessary to focus on the subject, the value is - f / 1.2 - f / 2.5, in this case, the main object will be in the zone of sharpness, and the background will be very blurred. When shooting at a wide aperture, certain difficulties can arise, given that the zone of sharpness is only millimeters, a small change in the angle of the camera entails a shift in focus. What to consider. Chromatic aberrations (colour distortion) can appear at a wide open aperture, while closing the aperture too much results in diffraction (loss of sharpness).

7. Aperture and types of lenses

Lenses, depending on their specifications, have a different minimum aperture value. The fastest lenses are those with a fixed focal length - aperture number from f/1.2 to f/2.8. On zoom lenses, you can often see a threshold of f values, such as 18-55 f3.5-5.6. This means that at a focal length of 18mm, the minimum aperture value will be 3.5, at 55mm - 5.6. Advantages of high-aperture lenses: high-aperture optics allow you to work in poor lighting conditions without the use of additional equipment and at low ISO; a small number of lenses in the lens design, which ensures the best image quality; soft and beautiful bokeh wide open.

For reference: one of the fastest lenses on the market is the Carl Zeiss Planar 50mm f/0.7, commissioned by NASA for the Apollo lunar mission. On the ground, this lens "lit up" in some of Stanley Kubrick's films.

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Knowing how to use your lens effectively has a much greater impact on the sharpness of your photo than choosing the lens itself. The aperture number is the most important of the shooting parameters that affect the technical quality of the image. The difference between different apertures of the same lens can be much more noticeable than the difference between different lenses at the same aperture.

	f/1.8
	f/2.8
	f/4
	f/5.6
	f/8
	f/11
	f/16
	f/22

Obviously, for the standard fast lens used in this test, sharpness is perfect at f/5.6, but f/4 is almost as good. f/1.8 is somewhat soft, which is natural for the maximum aperture. At f/11, the drop in sharpness due to diffraction is already noticeable, but not fatal, but at f/22, the picture is blurred quite significantly.

Lens aberrations

No lens is perfect. The laws of physics do not allow a beam of light to follow exactly the path that is prescribed for it by calculations made for an ideal optical system. This leads to spherical, chromatic and other aberrations, which cannot always be completely corrected. The center of the lens is usually perfect, but the closer to the edge, the more the light is distorted, scattered and refracted.

When the aperture is fully open, the film or sensor is exposed to light collected from the entire surface of the lens. In this case, the aberrations of the lens are fully manifested. By closing the diaphragm, we cut off part of the light flux passing through the edges of the lenses, allowing only the center, free from distortion, to participate in the formation of the image.

It would seem that the smaller the size of the relative aperture, the higher the image quality should be, but that was not the case. At the other end of the aperture value scale, an insidious enemy awaits us.

Diffraction

As the size of the aperture in the diaphragm becomes smaller, an increasing percentage of the light rays passing through the aperture touches its edges. In this case, the rays deviate somewhat from their original path, as if bending around the edge of the hole - this is diffraction. As a result, each point of the scene, even being strictly in focus, is projected onto the sensor no longer as a point, but as a small blurry spot called the Airy disk. Its size is larger, the smaller the aperture opening. When the diameter of the Airy disk begins to exceed the size of an individual array photodiode, blurring becomes apparent. Closing the aperture further only exacerbates the diffraction.

The resolution of modern cameras is so high that slight blurring of the image due to diffraction can be seen already at apertures from f / 11 and larger. Compact cameras with tiny sensors will generally not allow you to use apertures larger than f/8, because the small size of the photodiodes makes diffraction especially noticeable.

Sweet spot

The optimal aperture value is individual for each lens, but, most often, it lies in the region of two steps from the minimum, i.e. f / 5.6-f / 11, depending on the specific model. Open the aperture wider and optical distortion becomes more noticeable, stop the aperture and diffraction starts to blur the image.

The better the lens, the more worthy it looks at a fully open aperture. This is especially true for the edges of the frame. At large apertures, such as f/11-f/16, almost all lenses behave the same way.

The choice of aperture is a balance between sharpness itself and depth of field. Artistic taste, experience and a clear understanding of the photographic tasks facing you will help you immeasurably more than any theoretical reasoning. However, I will still try to make life easier for you.

Optimal Aperture Selection Strategy

• Find the aperture value at which your lens produces the best sharpness, and use that value whenever possible (usually f/8 or so).
• If you don't have enough light, or if you want to highlight the main subject with a shallow depth of field, increase the size of the aperture opening, but try not to open it completely unnecessarily.
• If the need has come, feel free to open the diaphragm and do not worry about it. In situations where you may need it, the aperture value is far from the most important factor limiting the sharpness of pictures. Shaking spoils the image much more ruthlessly than any lens aberrations.
• If you need a greater depth of field, stop down, but no further than f/11 for wide-angle lenses and up to f/16 for telephoto lenses.
• If you still lack depth of field, which shouldn't happen often, use f/16 for wide angle lenses and f/22 for telephoto lenses. In no case should you clamp the aperture harder - you will pay for an increase in depth of field with a too noticeable drop in overall sharpness.

That's all. By being aware of your equipment's weaknesses, you are able to avoid situations where they show up, which means you can exploit its strengths more effectively.

Thanks for attention!

Vasily A.

post scriptum

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Anyone who was not too lazy and read the instructions for the camera may not read further. But for those who are too lazy to do this, perhaps the “explanation on the fingers” will be informative.

In any camera, there is such a thing as an aperture. Photographers in jargon also call it a hole or a relative hole. The diaphragm is a kind of mechanism that is most often located in the lens and can have the property of narrowing and expanding.

As this hole narrows, less light reaches the camera's sensor. Thus, it is possible to regulate - if there is a lot of light, then due to the narrowing of the aperture, its amount is reduced, and the frame is exposed normally. The reverse action is also true - the larger the relative aperture, the more light will hit the camera sensor and, accordingly, you can shoot in fairly dark conditions.

But this is not the only useful property of the diaphragm. Aperture has a strong effect on the final result - the photograph.

There are two ways to influence an image with aperture. Firstly, the effect on the depth of field, and secondly, on the bokeh pattern. Since the article is intended for amateurs, of course, below we will definitely explain the meaning of these words, but for now we will make a small remark about aperture numbers - that is, about aperture designations.

The aperture is not measured in any units, that is, it is not a millimeter and not a second. It's just a number! And the larger the number, the smaller the hole.

The example below shows how the exposure of the image changes depending on the size of the aperture.

Aperture is usually denoted by the letter "F"

Another important fact about the aperture that you need to know is the relative value, it does not depend on the type of camera you are using. That is, if you measured (for example,) that, other things being equal, the aperture should be 5.6, then this parameter will be true for both a compact soap dish and a medium format camera.

Influence of aperture on depth of field

DOF stands for Depth of Field or Depth of Field. If you are photographing an object and focusing on it, then how sharp it will be and how far the space behind this object will be sharp depends primarily on the aperture. An example will demonstrate this best. Here the cakes are shot with different shutter speeds and apertures.

The pictures show how blurred the extreme cakes are to a greater or lesser extent, depending on how the aperture was opened. Depth of field can be calculated using simple formulas that are available on the Internet, but in reality, depth of field is calculated on purpose very rarely, more often they use the accumulated experience.

In addition to the aperture, the focal length of the lens also affects the depth of field. We will not go into the physics of the process in this article, we recommend just remembering - the larger the focal length of the lens used, the more the background will be blurred. That is, the telephoto blurs the background better than the width.

For example, in the photos above, the model was shot with the same aperture on lenses with different focal lengths.

Effect of aperture on bokeh

First of all, let's define what is bokeh? Bokeh is blurry, fuzzy. Most often, the name refers to the blurry background in the photo. We have already mentioned that the aperture is precisely responsible for the blurring of the background, what else to talk about then? The fact is that, along with optics, the shape of the aperture - the number of petals and so on, affects the bokeh pattern.

Modern manufacturers try to make the shape of the diaphragm opening as round as possible. But you can still find photos where the shape of the aperture appears in the bokeh.

The shape of the aperture is most clearly visible if there are bright dots in the background. For example, glowing light bulbs. Now you can often find pictures in which bokeh is artificially shaped in a special way. How to do this, we wrote in the article

Conclusion

We tried very hard not to overload the information with terms. We will be glad if, after reading, you finally get the instructions and read them. Much will become clearer to you. It is important for photographers to know and understand substances like aperture and ISO. These are the tools that every photographer needs and everyone should definitely try to shoot at the maximum open aperture and maximum closed aperture in order to understand the limits of their camera. And maybe your shots will become more expressive when the background is blurred and the main subject becomes even better as a result, or when shooting a landscape, you will no longer trust the automation, but clamp the hole all the way so that the foreground is worked out clearly and , and back.

Today, digital cameras with various automatic modes and scene programs practically free the photographer from having to think through and manually set shooting parameters. And in most cases, shooting in automatic mode, you can get really high-quality shots. However, in order to turn ordinary photographs into real masterpieces, you must be able to correctly use the photographic equipment at your disposal.

In particular, the correct aperture setting for a particular lens will provide optimal image sharpness much more than choosing the optics themselves. Don't try to find the best lens for every shooting situation - it just doesn't exist. It is much better to learn how to properly use the optics already at your disposal in order to fully reveal its strengths. For this, in particular, it is required to carefully consider the setting of the aperture value.

Camera aperture

Aperture is a special design in the form of thin hemispheres that are placed along the lens. With the help of these peculiar petals, the flow of light flux to the sensitive sensor of the apparatus is regulated. When you press the shutter button, the petals form a hole of a certain diameter, through which light seeps through. At the same time, aperture is the f-value that determines how wide the metal petals open.

The aperture scale ranges from f/1.2 to f32. At the same time, the pattern here is this: the smaller the f-number, the wider the petals will open and, accordingly, the more light fluxes will be on the surface of the sensitive sensor. By the way, this pattern often confuses beginners - they make the mistake of setting a larger aperture value in the hope of getting brighter pictures.

What does aperture affect? Firstly, it affects the overall brightness of the image, because the more the aperture is open (the smaller the aperture number), the more light will be on the sensor surface of the device. If you cover the aperture (set a value, for example, f / 16), then the pictures will be darker.

Secondly, the aperture determines the sharpness of the created image, and this is perhaps even more important for the photographer. The following principle applies here: the more you open the aperture, the more objects that are out of focus, that is, the background, are blurred. And vice versa, the more you stop the aperture, the more objects in the frame will turn out sharp. That is why lenses with a wide aperture range provide creative freedom not only in terms of depth of field, but also in the possibility of setting one or another shutter speed. Optics with a higher maximum aperture are usually heavier and more expensive.

Example of how the final image changes when the aperture value is changed from F4 to F22, 55mm focal length (82mm in 35mm equiv.), lens Pentax HD DA 55-300mm f/4-5.8 ED WR. Click to enlarge.

1 of 9

Focal length 50mm (82mm in 35mm equiv.), F4.0 aperture

Focal length 50mm (82mm in 35mm equiv.), F22 aperture

Thus, the aperture allows you to adjust the depth of field of the created photograph, as well as its brightness. Moreover, we can say that the difference between choosing one or another aperture value for one optics will be more significant than between different lenses when setting the same aperture value. The theory of photography tells us this rule: by opening the aperture, we can draw the viewer's attention to the central subject. By closing the aperture to a certain value, you can ensure that the objects you need in the frame are sharp. Everything seems simple, but in practice the photographer faces certain problems when setting the appropriate aperture value.

The problem is that the characteristics of any optics are not ideal. The light beam simply cannot be strictly directed along the path that the engineers who created this or that lens prescribed for it. If the center of the lens usually has almost ideal properties, then the closer to the edges, the more the light flux begins to distort and scatter. As a result, spherical or chromatic aberrations are inherent in any lens to varying degrees. If you cover the lens aperture, then the light flux penetrates the camera matrix only through the center, which is practically free from any distortion. But if you fully open the aperture, then various aberrations begin to fully manifest themselves here, which negatively affects the quality of the photographic image.

It would seem that in order to improve the quality and sharpness of the image, it is better to use a smaller relative aperture, that is, to cover the lens aperture. But it wasn’t there, because another trouble awaits us. When the hole becomes very small, the light rays begin to deviate from the original path, touching and bending around the edges of the lens. This phenomenon in photography is called diffraction. It leads to the fact that even objects that are in focus begin to blur a little. Moreover, the more you cover the aperture, the diffraction effect is enhanced.

On old cameras, this was not so noticeable, but the resolution of the sensors of modern devices is such that even a slight blurring of the points of the object being shot due to diffraction is clearly distinguishable in photographs already at f / 11 aperture. Diffraction becomes even more noticeable when shooting with a simple “soap box”, in which the physical dimensions of the matrix itself are smaller. Diffraction is also affected by the focal length, because the f-number is nothing more than the ratio of the relative aperture to the FR of optics. Accordingly, at the same aperture value, but in optics models with different focal lengths, the diffraction effect will manifest itself in different ways. In particular, diffraction is clearly visible at f/22 wide-angle, but the effect is less pronounced at long-focus optics.

Optimum lens aperture value

So, if you open the aperture wide enough, then optical distortions will become noticeable, but if you cover the aperture to a certain value, the picture will begin to blur due to diffraction. Due to these features of optics, a natural question arises, how to determine the optimal aperture value? A suitable aperture value will have to be selected for each model of optics. In most cases, the optimal aperture value is about two stops from the maximum value, that is, somewhere between f / 5.6 - f / 11. Most of all, lenses differ in image quality at the maximum aperture, and, conversely, at f / 11 - f / 16, the difference between the lenses is less noticeable. Therefore, optics that are designed and executed more efficiently, manifest themselves better at a fully open aperture.

450mm focal length, F5.8 aperture, very sharp foreground, but the lizard's tail is already blurry

When choosing an appropriate aperture value, you have to find a certain balance between the risk of distortion or blurring and the desired depth of field. It is most convenient to set the aperture in aperture priority mode (Av) or in full manual mode (M). Here you can give the photographer a few simple practical tips. By trying different apertures while shooting, you need to find one that gives a particular lens the best image sharpness. It is advisable to experimentally find this value and apply it in most shooting situations.

There may be several exceptions. For example, you may need more light or you need to focus on the main subject - then open the aperture, but be careful not to set the lowest aperture values ​​\u200b\u200b(f / 1.2 - f / 1.8). If you need a large depth of field so that as many objects in the frame as possible are in focus, then you will have to close the aperture a little.

82mm focal length, F8 aperture, sharp image of the main subject, good visibility and clarity of the background

For wide-angle optics, it is better to limit yourself to covering the aperture to f / 11, while when using long lenses, you can cover more - up to f / 16 - f / 22. Keep in mind that you still shouldn’t clamp the aperture too much, because in this case you will have to pay for the depth of field by blurring the image due to diffraction.

As practice shows, it is advisable to use f / 1.4 - f / 2.8 aperture values ​​\u200b\u200bwhen there is a lack of light. For portraits, apertures of f/4 to f/5.6 are usually suitable. At the same time, not the greatest depth of field (f / 2.8) when shooting a portrait allows you to separate the main subject from the background. To photograph group portraits with sufficient depth of field, you can set the aperture to f / 8 - f / 11. A larger aperture stop is used in landscape photography where every subject in the frame needs to be sharp and there is no need to draw the viewer's attention to the foreground.

So, try photographing the same scene with different apertures. Determine the optimal value for your lens, at which it provides the sharpest, highest quality image. If during the shooting you need to blur the background more strongly or, conversely, show all the objects in the frame as sharply as possible, then simply decrease or increase the aperture value by a couple of steps from the optimal value.

The aperture of a camera is one of three factors that affect exposure. Therefore, understanding the action of the aperture is a prerequisite in order to take deep and expressive, correctly exposed photographs. There are both positives and negatives to using different apertures, and this tutorial will teach you what they are and when to use which.

Step 1 - What is a camera aperture?

The best way to understand what a diaphragm is is to think of it as the pupil of the eye. The wider the pupil is open, the more light enters the retina.

Exposure consists of three parameters: aperture, shutter speed and ISO. The aperture diameter adjusts the amount of light entering the matrix, depending on the situation. There are various creative uses for the aperture, but when it comes to light, it's important to remember that wider apertures let in more light, and narrower apertures less.

Step 2 - How is aperture determined and changed?

Aperture is determined using the so-called aperture scale. On the display of your camera, you can see the F/number. The number means how wide the aperture is, which in turn determines the exposure and depth of field. The lower the number, the wider the hole. This may cause confusion at first - why does a small number correspond to a large aperture? The answer is simple and lies in the plane of mathematics, but first you must know what the f-stop series or the standard f-stop scale is.

Diaphragm row:f/1.4f/2,f/2.8f/4,f/5.6f/8,f/11,f/16f/22

The main thing you need to know about these numbers is that there is one exposure step between these values, that is, when moving from a smaller value to a larger one, half the light will enter the lens. In modern cameras, there are also intermediate aperture values ​​that allow you to more accurately adjust the exposure. The tuning step in this case is ½ or 1/3 steps. For example, between f/2.8 and f/4 there will be f/3.2 and f/3.5.

Now for more complex things. More precisely, why the amount of light between the main aperture values ​​\u200b\u200bis two times different.

It comes from mathematical formulas. For example, we have a 50mm lens with an aperture of 2. To find the diameter of the aperture, we have to divide 50 by 2 to get 25mm. The radius will be 12.5 mm. The formula for the area is S=Pi x R 2 .

Here are some examples:

50mm lens with f/2 = 25mm. The radius is 12.5 mm. The area according to the formula is 490 mm 2. Now let's calculate for f / 2.8 aperture. The diaphragm diameter is 17.9 mm, the radius is 8.95 mm, the hole area is 251.6 mm 2 .

Dividing 490 by 251 is not exactly two, but that's only because f-numbers are rounded to the first decimal place. In fact, the equality will be exact.

This is how the ratios of the diaphragm openings really look.

Step 3 - How Does Aperture Affect Exposure?

As the aperture size changes, the exposure also changes. The wider the aperture, the more strongly the matrix is ​​exposed, the brighter the image is obtained. The best way to demonstrate this is to show a series of photographs where only the aperture changes and the rest of the parameters remain unchanged.

All images below were taken at ISO 200, shutter speed 1/400 sec, no flash, and only the aperture was changed. Aperture values: f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22.

However, the main property of the aperture is not exposure control, but a change in the depth of field.

Step 4 - Depth of field effect

Depth of field is a vast topic in itself. To open it, you need several dozen pages, but now we will consider it very briefly. We are talking about the distance that will be transmitted sharply in front and behind the subject.

All you really need to know, in terms of the relationship between aperture and depth of field, is that the wider the aperture (f/1.4) the shallower the depth of field, and the narrower the aperture (f/22) the greater the field of field. Before I show you a selection of photos taken with different apertures, take a look at the chart below. It helps to understand why this is happening. If you do not understand exactly how it works, it's okay, as long as it is important for you to know about the effect itself.

The image below shows a photo taken at f/1.4. It has a pronounced DOF effect (Depth of Field)

Finally, a selection of photos taken in aperture priority, so the exposure remains constant, and only the aperture changes. The aperture row is the same as in the previous slide show. Notice how the depth of field changes as you change the aperture.

Step 5 - How to use different apertures?

First of all, remember that there are no rules in photography, there are guidelines, including when it comes to choosing an aperture. It all depends on whether you want to apply an artistic technique or capture the scene as accurately as possible. To make it easier to make a decision, here are some of the most traditionally used aperture values.

f/1.4: Excellent for shooting in low light, but be careful, this setting has very little depth of field. Best used for small objects or to create a soft focus effect.

f/2: The use is the same, but a lens with this aperture may cost one third of a lens with aperture 1.4

f/2.8: Also good for low light conditions. It is best used for portraits, as the depth of field is greater and the entire face will be included, not just the eyes. Good zoom lenses usually have this aperture value.

f/4: This is the minimum aperture used to take a picture of a person in sufficient light. Aperture can limit autofocus performance, so you risk missing wide open.

f/5.6: Good for 2 person photography, but for low light it is better to use flash light.

f/8: Used for large groups as it guarantees sufficient depth of field.

f/11: At this setting, most lenses are at their sharpest, so it's good for portraits.

f/16: Good value when shooting in bright sunlight. Great depth of field.

f/22: Suitable for shooting landscapes where attention to detail in the foreground is not required.