In use:

Aperture itself has nothing to do with focal length, it is a facility to control the amount of light entering in cooperation with shutter.

If it matters, it's depth of field. The aperture is small, the depth of field is large (the clear range before and after focusing is large).

So you can find some information about depth of field, which will be difficult to talk about here for a while.

theoretically

Aperture value is calculated by focal length and aperture:

Here, the aperture is also called relative aperture F.

The scene is focused by the lens, and the brightness of the image,

1, depending on the lens aperture of the input light. The lens with large aperture has a large amount of light and bright image. If you take pictures in the dark, you only need a small amount of light to take pictures with a large aperture lens.

2. In addition, no matter how big the aperture of your lens is, if the focal length is long and the lens is far from the focal plane, the focal plane will become dark.

Therefore, the aperture and focal length of the lens will affect the imaging brightness.

In order to use unity, a parameter: relative aperture f is introduced, which combines the influence of focal length and aperture on light into this parameter.

The relative aperture of the lens is denoted by f, and the relationship between them is as follows:

F=f/D

F is the focal length and d is the effective aperture of the lens.

With the concept of relative aperture, we can know that the relative aperture f of any camera is equal and the brightness of the focal plane is equal (that is, the light transmission ability is equal).

It should be pointed out here that:

A. The luminous flux has a linear relationship with the effective aperture area of the lens, and the circular area is twice smaller than the diameter d, so the luminous flux is twice different for every difference of the F value. The standard series value of F value is:1; 1.4; 2; 2.8; 4; 5.6; 8; 1 1; 16; 22; 32; The luminous flux between every two adjacent values is twice different.

B in the formula, f is directly proportional to f (focal length), and the f value of the zoom lens will also change when zooming. As can be seen from the formula, f changes by 10 times, and f also changes by 10 times.

But in fact, the change of f value is not so much, and some even remain unchanged. Of course, it is better to change a little, and it is better to stay the same. At least its design is better.

Finally, I will talk about it from two aspects: use and theory. The reason is that you don't need to care about its theoretical problems when using it. As long as the aperture is used well, it will be confusing and confusing, especially for beginners. If you are interested, look at the theory again and see how it came about.

Why is the depth of field related to aperture and focal length?

Aperture is a mechanical device that can change the size of the middle hole of the camera lens, and shutter is a device (mechanical or electronic) that controls the exposure time. The combination of the two controls the exposure.

Depth of field is an optical concept. According to the formula of "1/ image distance = 1/ object distance+1/ focal length", there is a one-to-one correspondence between object points and image points, but this is also an approximate proportion. In fact, a distance before and after the object point can also be clearly imaged on the photosensitive original. What we call "depth of field" refers to the range of clear imaging. Therefore, the depth of field can also be simply understood as the clear imaging range of the subject on the photosensitive element (film, CCD, CMOS). Factors related to depth of field include focal length and aperture.

Aperture, also known as "relative aperture", the lens of a camera uses an assembly of multiple blades to control the intensity of light entering the lens. This lens group is called the aperture. Through reasoning and calculation, it is concluded that the illumination of the image (imaged on the photosensitive element) is not only related to the brightness of the scene itself and the magnification of the image, but also proportional to the square of the lens aperture diameter d; It is inversely proportional to the focal length f of the lens, and the value of D/F is called the "relative aperture" of the lens. For convenience, the reciprocal F/D of the relative aperture is called the aperture number, also called the f number. Therefore, the smaller the ratio, the larger the aperture and the greater the luminous flux per unit time.

When shooting, the relationship between depth of field and aperture and focal length can be summarized as follows:

1, the greater the focal length of the lens, the smaller the depth of field, and vice versa. For example, under the same aperture, the depth of field of 300mm is shallower than that of 125mm.

2. The larger the lens aperture, the greater the depth of field (that is, the smaller the relative aperture of light), and vice versa; (It can also be understood that the smaller the aperture index, the shallower the depth of field. For example, at the same focal length, the aperture index of F 1.0 is larger than that of F22. The depth of field of F 1.0 is shallower than that of F22.

In addition, the object distance also affects the depth of field. Generally speaking, the greater the object distance, the greater the depth of field. Usually, objects at infinity can be clearly imaged after a specific object distance (the specific object distance is determined by the focal length and aperture of the lens, but the aperture size can also be determined by controlling the aperture size). This depth of field is called "hyperfocal distance".

Is there a relationship between focal length and aperture size?

Depending on whether your lens has a constant aperture or a non-constant aperture, ordinary digital cameras almost always have a non-constant aperture, that is, with the increase of focal length, the maximum aperture that can be used will decrease.

For SLR cameras, depending on the lens parameters, such as 18-55mm, the non-constant aperture f/3.5-5.6, that is to say, the maximum aperture available at the wide-angle end of 18mm is f/3.5, the telephoto end of 55mm is reduced to f/5.6, and the constant aperture is 70-200mm f/2.

The structure of constant aperture zoom lens is relatively more complicated, so the price is much higher.

What is the relationship between aperture and focal length in photography?

Aperture is a device that adds an aperture grating with variable area inside the lens to control the luminous flux of the lens. The focal length is the distance from the center of the lens in the camera to the imaging plane of the sensor.

By changing the aperture size, the depth of field can be changed, that is, after focusing, the camera lens can form a clear image in the range before and after focusing. Simply put, the larger the aperture, the smaller the depth of field, the smaller the aperture and the greater the depth of field; The longer the focal length, the smaller the depth of field, the shorter the focal length and the greater the depth of field. Such as the common 18-55 lens, at the wide-angle end of 18mm, as long as the aperture value is greater than f 1 1, the subject is clear from 1 m to infinity. Clever use of aperture and different focal lengths to control the depth of field, no need to focus in an emergency, which is conducive to snapshot.

Does the focal length of SLR lens have anything to do with aperture?

This is very important.

Aperture f value = effective aperture/lens focal length

Therefore, it is obvious that the larger the focal length, the smaller the F value when the effective aperture of the lens remains unchanged.

So for some low-end lenses that don't do much processing on the aperture (such as 18-55), the maximum aperture at the end of 18 is larger than the end of 55 (the larger the aperture, the smaller the f value).

On the other hand, if the aperture is constant and the focal length is larger, the effective aperture needs to be larger. So some telephoto guns have large caliber.

The parameter of aperture is defined because it can fully represent the amount of light entering. That is to say, regardless of the focal length, as long as the aperture is the same, the amount of light entering is the same. So whether the focal length is 18 or 55, the exposure under the same aperture is the same.

Aperture, depth of field, focal length, the relationship between them?

Formula:

Deep prospect range ⊿ l 1 = (f? δ? I↑2)/(F′↑2+F？ δ? I)

Back depth of field range ⊿ L2 = (f? δ? I↑2)/(F′↑2-F？ δ? I)

⊿L=⊿L 1+⊿L2. Quan Jingshen Mountains.

Where: f '- the focal length of the lens.

F- the aperture number of the lens.

δ —— allowable diameter of dispersion circle

I —— the distance from the plane of the focusing object to the lens.

Note: No mathematical formula is entered here, and the formula in Word can't stick to the foundation, so we have to do it. ↑2 represents the square of the previous value.

The allowable diameter of the dispersion circle should be11000 of the focal length of the standard lens, 135 The standard lens of the camera is 50mm, and the allowable diameter of the dispersion circle is 0.05mm.

I calculated with the formula, if the aperture of the 50mm lens is 2 and the distance is 10 m, then ⊿L 1=2.86m,

⊿ L2 = 6.67m, so the depth of field at this time ranges from 7. 14m to 16.67m, which is consistent with the data found in Jing Shenbiao. Note that it is very troublesome to change all millimeters into meters when calculating.

The data you gave, ⊿ L 1 = 15.6m, ⊿L2 is infinite, then the clear distance should be from 14.4m to infinity. Because the focus is 30 meters, which is infinite, I can't find it in the depth of field table. I don't know if it's right. It should be noted that this is calculated according to the standard lens of 50 mm If you use telephoto, you can substitute the focal length of your lens and do the calculation yourself.

There is a formula, but the calculation is troublesome. It is estimated that no one will use it to calculate the depth of field.

What is the relationship between aperture, focal length and depth of field?

Aperture f value = lens focal length/lens aperture diameter

According to the calculation method of aperture value, the longer the focal length, the larger the actual diameter of the aperture, and the shorter the focal length, the smaller the actual diameter of the aperture.

In other words, the minimum usable aperture of a long focal length lens can be made smaller, and if the minimum aperture of a short focal length lens is too small, diffraction will occur.

For example, there are three shots:

The focal length of lens A is 50mm and the maximum aperture diameter is 25mm, so the aperture coefficient is 50/25 = 2. We're talking about f2 shots.

Lens B has a focal length of 35mm, a maximum aperture diameter of 17.5mm and an aperture coefficient of 35/ 17.5 = 2, which is also called f2 lens.

The focal length of lens C is 100mm, and the maximum aperture diameter is 25mm, so the aperture coefficient is 100/25 = 4. We say it's a shot of f4.

This is the same as the aperture you choose for photography. Choosing the aperture in photography is to change the aperture size by blocking a part of the lens with the shutter blade. See the picture.

Therefore, the aperture f value = focal length/aperture diameter is suitable for the maximum aperture of the lens, not the aperture set when shooting.

Relationship between aperture value and focal length value of camera

Generally speaking, using the maximum or minimum aperture of a lens can not get very satisfactory imaging quality! When the aperture is fully opened, the light will pass through almost the whole area of the lens and form an image on the photoreceptor. In this way, the defects caused by insufficient precision in the production process will be exposed in the final image.

What is the effect of aperture size?

In photography, aperture control is one of the most important basic skills. Because the aperture value can affect the depth of field effect, shutter speed, imaging style and imaging quality!

Image quality-use the appropriate aperture to obtain high-quality images.

Generally speaking, using the maximum or minimum aperture of a lens can not get very satisfactory imaging quality! When the aperture is fully opened, the light will pass through almost the whole area of the lens and form an image on the photoreceptor. In this way, the defects caused by insufficient precision in the production process will be exposed in the final image.

Therefore, we narrow the aperture so that only a part of the central area of the lens, not the whole area, passes through the light participating in the imaging. In this way, the manufacturing error of the opaque part of the lens edge has no chance to destroy the imaging quality, so the imaging quality has been improved to a certain extent. So according to this theory, the smaller the aperture (same lens, same focal length), the better the imaging.

But in fact, we will encounter another problem: if the aperture of the lens becomes too small by narrowing the aperture, the diffraction phenomenon of light passing through the aperture will be very serious. And this optical phenomenon will also reduce the imaging quality of the lens!

Because aperture value = aperture diameter/lens focal length, a smaller aperture is also used. The shorter the focal length of the lens, the smaller the aperture will be. According to this relationship, it is easy to find that the shorter the focal length of the lens, the easier it is to reduce the imaging quality because of the diffraction of light when taking photos with smaller aperture. Think about it. Even if the aperture value of a lens with a focal length of 300mm drops to f32, its aperture size is exactly the same as that of a lens with a focal length of 30mm and an aperture of F3.2.!

For example, I have a 70-300mm lens in my hand. I specially tested its imaging quality at 300mm end, and the result is that the smallest f29 and f32 are the best apertures!

Is the smaller the aperture, the better the imaging quality? Not really, because too small an aperture means too small an aperture. When the aperture is too small, too little light passes, which is not conducive to high-quality imaging. Even in extreme cases, light will be diffracted, thus reducing the resolution. Therefore, in terms of imaging quality, the smaller the aperture, the better.

It is neither the bigger the better nor the smaller the better, so there must be an optimal imaging aperture in the lens aperture. So, what is the best lens aperture of digital SLR camera at present? Generally speaking, for Quan Huafu lens, the best aperture is around F8 or F 1 1. For APS-C digital SLR lenses (such as Nikon DX lens, Canon EF-S lens, Sony DT lens, etc. ), the best aperture is usually around F8. For the lenses used in the 4/3 system, such as the lenses of ZUIKODIGI-TAL of Olympus and Panasonic/Leica, the optimal imaging aperture is often larger, between F5.6-F8 and F8.

In addition, it should be noted that not all lenses can obtain excellent optical quality when the aperture is reduced to above F5.6, otherwise those lenses with large aperture will be completely meaningless. In fact, many high-quality large aperture lenses can usually obtain excellent optical quality by narrowing one or two apertures.

Depth of field effect-change the aperture value to present different depth of field.

Aperture is not only responsible for controlling the intensity of light entering the camera, but also holds another important key "depth of field". The so-called depth of field refers to the clarity of the subject before and after shooting. The shallower the depth of field, the more blurred the background and the more prominent the subject. The deeper the depth of field, the clearer the background and subject will be.

The larger the aperture, the shallower the depth of field. The smaller the aperture, the deeper the depth of field. For example, the depth of field of aperture F4 will be shallower than F8. A large aperture can blur the background and highlight the subject. A smaller aperture will make the depth of field deeper, and the messy background will cause unnecessary interference to the subject.

SLR cameras have a so-called depth of field preview button. When the depth of field preview button is pressed, from the viewing window ......

What is the relationship between camera focal length and aperture?

Use an appropriate aperture to obtain a high-quality image.

In photography, lens aperture control is one of the most important basic skills. Because the aperture value can affect the depth of field effect, shutter speed, imaging style and imaging quality! However, the influence of aperture size on imaging quality is mainly discussed here.

Generally speaking, using the maximum or minimum aperture of a lens can not get very satisfactory imaging quality! When the aperture is fully opened, the light will pass through almost the whole area of the lens and form an image on the photoreceptor. In this way, the defects (scale errors) caused by insufficient precision in the lens production process will be exposed in the final image. Therefore, we narrow the aperture so that only a part of the central area of the lens, not the whole area, passes through the light participating in the imaging. In this way, the manufacturing error of the opaque part of the lens edge has no chance to destroy the imaging quality, so the imaging quality has been improved to a certain extent. So according to this theory, the smaller the aperture (same lens, same focal length), the better the imaging. But in fact, we will encounter another problem: if the aperture of the lens becomes too small by narrowing the aperture, the diffraction phenomenon of light passing through the aperture will be very serious. And this optical phenomenon will also reduce the imaging quality of the lens!

Because aperture value = aperture diameter/lens focal length, a smaller aperture is also used. The shorter the focal length of the lens, the smaller the aperture will be. According to this relationship, it is easy to find that the shorter the focal length of the lens, the easier it is to reduce the imaging quality because of the diffraction of light when taking photos with smaller aperture. Think about it. Even if the aperture value of a lens with a focal length of 300mm drops to f32, its aperture size is exactly the same as that of a lens with a focal length of 30mm and an aperture of F3.2.!

!

Shutter speed will also affect the imaging quality of the lens.

First of all, I still want to say a "general experience", that is, if the shutter speed is expressed by 1/M seconds, the lens focal length of 135 camera is expressed by n mm. Then when shooting with a hand-held camera, it is generally believed that m needs to be greater than n, so that the image will not be blurred because of hand jitter. It is also more strictly proposed that m should be greater than 2N to ensure the clarity of the image. In fact, the above "general experience" is not directly related to this article, because this article is completely around the lens, and it also distinguishes between high-end lenses and cheap lenses. However, due to the above-mentioned "general experience", many people blindly pursue faster shutter speed. When they expect to get a clear image, they always think that "even if it is only a little faster, it will be clearer." This is a problem!

As we all know, SLR cameras have a weakness: at the moment of shooting, the movement of the reflector will make the whole camera vibrate, which will lead to blurred images. To solve this problem! At the moment of shooting, we can observe the obvious vibration coming from the frame, and even hear the sound from various parts of the lens because of poor combination! At this time, the imaging is naturally unclear.

Strong enough to "guess more than n" or even "m more than 2N", which is obviously the most ideal. Only when the value of n is large and the light is insufficient, such as taking pictures indoors, in the forest or at dusk or dawn, can we consider reducing the shutter speed. If the aperture is f8 and the sensitivity is ISO200, then the shutter speed is only1/60s, and it is meaningless to try to improve the speed. Because whether you open the aperture or improve the sensitivity, the image quality will drop significantly. In this way, we reduce the aperture to f32, reduce the sensitivity to ISO 100, and add PL filter, the shutter speed can be reduced to 1.5 seconds.

Always beware of the influence of glare on image quality.

There may be nothing we can do about the dazzling light that is connected by colored spots of different sizes. Because that kind of glare is caused by the presence of particularly bright highlights in the picture. Such as the sun or street lamps. These things exist in the picture, and if they are blocked, they can't be photographed. Although high-grade lenses can avoid glare to a greater extent, sometimes such glare is quite beautiful. For another most common glare, we can reduce its influence on the picture in our own way.

In fact, glare is not only observed through lenses. We can observe it with our own eyes: open a book, lift it with our left hand, look at the sky, and I ......

Relationship between shutter speed of focal length aperture

Focal length-refers to the distance from the optical center of the lens to the focal plane of the camera (focal plane is photosensitive film on the film machine, and refers to the photosensitive element of the camera on the digital camera, such as CCD or CMOS). For a standard lens of 50mm, 50mm does not represent "the distance between the lens and the subject".

Aperture-A device on a lens that can change the size of the incident aperture. The larger the incident aperture, the greater the amount of light entering.

A shutter is a device on a camera that can change the length of light. The faster the shutter speed, the less light enters.

Aperture is closely related to shutter, and focal length is not directly related to shutter and aperture, but only affects photographic composition and perspective modeling.

The relationship between aperture and shutter conforms to a law called "reciprocal law". To put it simply, only under proper illumination can photosensitive materials get correct exposure and get properly exposed photos. This suitable exposure is influenced by four factors, namely, the comprehensive value of the field light conditions, the shutter value, the aperture value and the ISO (sensitivity) value. When the ISO value is fixed, the shutter value and aperture value conform to the law of reciprocity under certain lighting conditions.

For example, ISO and light conditions are unchanged, the shutter value of the on-site prompt is1125 seconds, and the aperture value is f/8, so that the correct exposure can be obtained. If you want to change the shutter value to 1/250 seconds, you must change the aperture value to f/5.6 to get the correct exposure. Conversely, if the aperture value is changed to f/ 1 1, the shutter value should be changed to 1/60s to ensure correct exposure.

To sum up, when you get a correct exposure combination, if you enlarge the aperture, you must speed up the shutter, and vice versa.

Three characteristics:

Focal length-short focal length, large viewing angle, large depth of field, wide picture, etc. Long focal length, small viewing angle, small depth of field, compressed viewing angle and so on. The focal length of standard lens accords with people's visual habits.

Aperture-large aperture, large luminous flux and small depth of field; Small aperture, reduced luminous flux and increased depth of field.

Shutter-high-speed shutter, less light, curing moving objects; Low speed shutter, stronger light, showing moving objects.

As mentioned above, you can set different combinations according to your own shooting needs, which can not only get accurate exposure photos, but also meet your needs of expressing the subject.

Tip:

1. Reciprocity law will fail in both too bright and too dark environments, which is the famous "Reciprocity Law Failure". The remedy is "light plus dark", and the correct exposure is obtained through the "exposure compensation" provided by the camera.

2. The shutter speed should consider the influence of hand-held jitter. The method is as follows: once the shutter value (also called safety shutter) is set by using the reciprocal of the focal length of the lens, such as 100mm lens, the shutter speed should be set to not less than1125 seconds. Second, fix the camera with a tripod or other methods. Third, practice "iron hand skills" (joking).