Aperture and depth of field in optics when did you learn junior high school, high school or universi

It's up to you, but if you want to learn, you can do it now. If you want to know a little bit about it, then those who can take pictures can say a little bit. If you want to understand the right concepts, you can read books on geometric optics. Books that talk about photography alone don't necessarily explain it clearly.

If you go to university to study again, it depends on what major. Majors such as optical engineering are to be studied in geometric optics. There are also opportunities to study majors related to photography, but other majors are not necessarily studied, and you can go to public elective courses.

Aperture, strictly speaking, should be called "number of apertures", which is the reciprocal of the relative aperture, which is the diameter of the entrance pupil divided by the focal length. The entrance pupil is the image of the aperture diaphragm in the whole system, and it is the common entrance to all imaging rays. The larger the pupil, the more energy it receives for a given object, the brighter the image, and the greater the ability to distinguish details.

Strictly speaking, any object can only be clearly imaged in the conjugated image surface, but we found that some photos can see the front and back of the main person, such as the mountains and buildings behind them. This is because the optics have a depth of field. Depth of field is the extent of space in which an object can be clearly imaged in front of and behind it.

The reason for the depth of field is that any light energy receiver, including the human eye, is an object that can only distinguish certain details, and finer details cannot be distinguished. In this way, when the human eye observes**, if it is not the light from the conjugated object surface, but the light from other scenes in front of and behind the object, it will get a diffuse spot on the image plane, if this diffuse spot is small enough, the human eye still looks like a point, then the main depth range of the space in front of and behind the object is the depth of field. For a photographic lens with a certain focal length, the larger the entrance pupil, the larger the relative aperture, the smaller the number of apertures, and the smaller the depth of field.

If you want to take landscape photos and want the foreground and background to be clear, you should choose a larger number of apertures, that is, a smaller relative aperture, and the depth of field can be larger. If you want to shoot close-ups of people or flowers, highlighting the main subject and blurring the foreground and background, you should choose a smaller number of apertures, i.e. a large relative aperture, and the depth of field can be smaller. Of course, under certain lighting conditions, the smaller the number of apertures, the larger the relative aperture, and the more light energy enters, in order to be correct, a shorter time should be chosen.

On the contrary, if the number of apertures is larger, you should choose a longer ** time.

Middle School Physics. Find a junior high school student and ask.

The size of the depth of field is first related to the focal length of the lens, and the lens with a long focal length has a small depth of field and a lens with a short focal length with a large depth of field. Secondly, the depth of field is related to the aperture, and the smaller the aperture (the larger the value, e.g. the aperture of f16 is smaller than the aperture of f11), the greater the depth of field; The larger the aperture (the smaller the number, e.g. the smaller the aperture is greater than the depth of field.) Second, the foreground depth is smaller than the rear depth of field, which means that after precise focus, only a short distance in front of the focus point can be clearly imaged, while objects in a long distance behind the focus point are clear.

The depth of space that can be seen clearly by the eye at the same time is called the imaging depth of the eye, which is the depth of field. Depth of Field Calculation Formula: Depth of Field (2 * Diameter of the Diffuse Circle * Square of the Focal Length of the Lens * Aperture Value * Square of the Focus Distance) (4th power of the focal length of the lens d Square of the diameter of the diffusion circle * Square of the Aperture Value * Square of the Focus Distance) As can be seen from the formula, the rear depth of field > the foreground depth.

As can be seen from the formula for calculating the depth of field, the depth of field is related to the aperture used by the lens, the focal length of the lens, the shooting distance, and the requirements for image quality (expressed as the size of the allowable dispersion circle). The effects of these main factors on depth of field are as follows (assuming all other conditions do not change): 1) Lens aperture:

The larger the aperture, the smaller the depth of field; The smaller the aperture, the greater the depth of field; (2) Lens focal length The longer the focal length of the lens, the smaller the depth of field; The shorter the focal length, the greater the depth of field; The farther the distance, the greater the depth of field; The closer the distance, the smaller the depth of field.

The longer the focal length, the shallower the depth of field, such as the wide-angle lens 14mm, the same as the telephoto 300mm lens, the aperture, the subject 3m distance, then the wide-angle depth of field can be clear from the subject to infinity, while the telephoto only the target and the scene of a short distance behind are clear, and the others are blurred, so in order to highlight the subject, the telephoto lens is generally used to blur the background.

The aperture is a mechanical device in the camera lens that can change the size of the middle hole, and the shutter is a device (mechanical or electronic) that controls the length of time.

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 the object point and the image point, but this is also an approximate ratio. In fact, a distance between the front and back of the object can also be clearly imaged on the original photosensitive element, and the "depth of field" we mean the range of clear imaging.

Therefore, depth of field can also be simply understood as the clear image range of the subject on the image sensor (film, CCD, CMOS). Factors that affect the size of the depth of field include focal length and aperture.

Aperture, also known as "relative aperture", is a component of multiple blades that controls the intensity of light entering the lens. This lens assembly is called the aperture. After reasoning and calculation, the law is obtained:

The illuminance of the image (imaging on the image sensor) is not only related to the brightness of the scene itself and the anti-large (or small) magnification of the image, but also proportional to the square of the diameter d of the aperture of the lens; Inversely proportional to the focal length f of the lens, the value of d f is called the "relative clear aperture" of the lens, and the reciprocal f d of the relative clear aperture is called the number of apertures, also known as the f number. Therefore, the smaller the ratio, the larger the aperture and the greater the amount of light per unit of time.

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

1. The larger the focal length of the lens, the smaller the depth of field, and vice versa. For example, a depth of field of 300mm is shallower than a depth of field of 125mm at the same aperture.

2. The larger the aperture of the lens, the greater the depth of field (i.e., the relative clear aperture is smaller), and the smaller the depth of field; (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 is greater than the depth of field at f22 and shallower than at f22.

In addition, the size of the object distance also affects the depth of field, generally the larger the object distance, the greater the depth of field, usually after a specific object distance to infinity of the object can be clearly imaged (the specific object distance is determined by the focal length and clear aperture of the lens, of course, the size of the control aperture can also determine the specific size of the object distance), this depth of field is called "hyperfocal length".

Aperture f-number = focal length of the lens and diameter of the lens aperture.

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 lenses: A, B, and C

A lens has a focal length of 50mm and a maximum aperture diameter of 25mm, so the aperture factor is 50 25 2, we say it is a lens of f2;

The focal length of the B lens is 35mm, the maximum aperture diameter is 17 5mm, and the aperture factor is 35 17 5 2, we also say that it is a lens of f2;

If the focal length of the C lens is 100mm and the maximum aperture diameter is 25mm, the aperture factor is 100 25 4, and we say that it is an F4 lens

It's not the same as the aperture you choose for photography. When choosing an aperture when shooting, the aperture size changes by blocking a part of the lens with the blades of the shutter. See figure.

Therefore, the aperture f-number = focal length The aperture diameter applies to the maximum aperture of the lens, not the aperture set at the time of photography.

The longer the focal length, the smaller the depth of field.

For zoom aperture lenses, the maximum aperture decreases as the focal length increases.

For zoom fixed aperture lenses, the maximum aperture does not change with the focal length.

Practice more, memorize it when you use it proficiently.

Personally, I feel that if you want to ensure that the depth of field is shallow, the F number is small! If you practice more and shoot more, you will understand everything, and the theory is not as fast as the practice!!

For example, there is a family that has built a water tower to form a water supply system, and now wants to increase the flow of water from the tap, there are different ways: 1Increase the pressure on the water tower.

2.Turn on the valve of the large faucet. 3.

Thicker water pipes are used. Different ways can affect the flow of water from a faucet. You say, is it to increase the pressure of the water tower to have a greater water flow, or to thicken the water pipe to have a greater water flow?

Again, there are several different factors that affect the depth of field: the focal length of the lens, the aperture value, and the shooting distance (the distance of the subject from the camera lens).

The second question, the larger the aperture, the smaller the depth of field, omits a premise: the rest of the conditions remain the same, that is, the focal length and shooting distance of the lens remain the same.

If you open the aperture at the same time, shorten the focal length of the lens (for example, the aperture used for the original 200 mm lens is now changed to the aperture of the focal length of 28 mm), and at the same time change the shooting distance from the original 1 meter to 20 meters, then, the aperture is widened, but the depth of field is larger.

Using a prime lens as an example, it's a little easier to understand. For example, if you shoot with a 50mm lens, you can get the shallowest depth of field (i.e., the maximum bokeh effect) at this setting: for aperture, the closest shooting distance that can be focused with the lens.

For zoom lenses with non-constant apertures, you will see what you call shooting with the telephoto end, but the aperture becomes smaller, which presents a dilemma: should I use a large aperture at the wide-angle end or a smaller aperture at the telephoto end? This is to compare through actual shooting to see which kind of background bokeh effect is good.

In general, it is difficult to shoot the ideal background bokeh effect with a non-constant aperture zoom lens (this kind of lens is generally lower**), and if you want to get a beautiful background bokeh effect, you must either use a medium telephoto prime lens with a large aperture, or use a medium telephoto zoom lens with a constant large aperture. Why are the ** of both lenses relatively high? Of course, it is because it is difficult to make and the cost is high.

1.Take pictures with focus, right? For example, if you want to shoot you, you have to focus on you, and the background is out of focus.

If you're right or wrong, and you're in focus, and the background is clear, and you're blurred, that means you're out of focus, and the background is in focus. So, what's in focus is in the depth of field.

How long is the depth of field? It can be 1 mm, it can be 10 meters, or it can even be infinite. Anything that can be shot clearly, and what is not blurred, is in the depth of field. It's blurred, just outside the depth of field.

2.The larger the aperture, the smaller the depth of field; The longer the focal length, the smaller the depth of field. The closer the distance, the smaller the depth of field.

Three factors, aperture, focal length, distance.

The aperture is easy to understand, not to mention, and he wants to be independent, and the latter two do not affect each other.

Focal length and distance actually affect each other, so you'll get confused.

In general, the effect of focal length is greater than that of distance.

For example, if you want to shoot a person who is in the frame from head to toe, then the longer the focal length, the farther away you will be from the frame, so that the whole person can be left in the frame. However, the depth of field will also be less, which means that the background will be more noticeable.

The closer the distance, the shallower the depth of field, which means that you shoot this person, for example, with a focal length of 200mm. When the whole person can be photographed, the background blur is not obvious. But as you get closer, when you can only reach half of your body, the depth of field becomes smaller.

The background blur is more noticeable. The reason is because you walked in. But the composition has also changed.

So the last two can actually be summed up in one sentence: In the case of the same composition, the smaller the shot, the smaller the depth of field.

3.It's quite normal that the telephoto end doesn't give you a wide aperture. Background blur is a matter of money. A lens that can reach an aperture at 300mm costs tens of thousands of RMB. Is your all-in-one possible for you?

It's easy to get a feel for bokeh.

Just your all-in-one machine, shoot a small thing, such as a coin, use the longest focal end, go to the closest, the maximum aperture that can be used, try it?

Hehe, depth of field is the range where the front and back of the focus can be clearly imaged. I don't understand when you say "close-up" whether you mean a telephoto cannon or a macro head? If they have the same aperture, the depth of field at a wide angle (e.g. 24mm) will definitely be larger than that of XZP (70-200), and XZP will blur the background well.

Small depth of field = maximum aperture + as close as possible subject distance + long focal length lens, which is more correct. When shooting macro, you will find that the shallow depth of field is scary, whether it is a DSLR or a card. The aperture of the low-end lens is not constant, Nikon's 24-70 **hehe.

In order to reduce costs, many lenses do such as 28-135 floating aperture, but even the aperture background blur of telephoto lenses is obvious. Depth of field is also related to the size of the imaging element, so even if the aperture focal length of the 1 card is the same as that of the DSLR, the background blur of the SLR will not be captured. (Except for telephoto cameras, the CCD is small but the focal length is large, and it can play the ** of the bokeh background).

I studied engineering optics in my sophomore year, and I remember that there was a particularly disgusting formula for the diffuse circle or something, but we usually shoot a ** and don't engage in optical research, just by feeling. Just try more, I started thinking about these at the beginning, how can I blur the background with a small card, and it's strange, the aperture is not good? Later, I pondered and pondered, and I understood that the depth of field is not as simple as the aperture.