How to understand hyperfocal distance?

Basic definition hyperfocal distance: hyperfocal distance

Focusing on a certain point in the distance makes the other extreme of depth of field just infinite, and the shortest photographing distance from infinity to depth of field is called "hyperfocal distance distance". If the focus is set to hyperfocal distance distance first, it will fall within the depth of field from half of hyperfocal distance distance to infinity.

Because the back depth of field of the lens is relatively large, people call the distance that can be clearly imaged after focusing as hyperfocal distance. Fool cameras generally use hyperfocal distance, which makes use of the feature that the scene can be clearly imaged at a certain distance with a short-focus lens, omitting the focusing function. Therefore, generally, low-grade fool cameras can't focus automatically, so they can only use hyperfocal distance. As mentioned earlier, "clarity" is not an absolute concept, and the scenery in hyperfocal distance is not really clearly imaged. Because there is no focus, it must be blurred, but the degree of blur is generally acceptable. This is the reason why the negative film taken by a fool's camera can't be enlarged too much.

How to understand hyperfocal distance and hyperfocal distance?

Hyperfocal distance's original calculation formula is:

Hyperfocal distance = lens focal length+(the square of lens focal length divided by the product of c and f). F is the aperture coefficient, so I won't say much. This C is the diameter of the diffusion circle. In the previous textbooks, it was set to 0.05, that is, 1/20 mm. The Jing Shenbiao on the old lens was drawn according to 1/20 mm. If you don't believe me, you can calculate it according to your lens. Now it is set to 1/30mm, and some of them are set to1/40.

Basic classification

I have seen "f=" in the English manual of the camera, so the number behind it is usually its focal length, that is, the focal length. For example, "f=8-24mm, 38- 1 15 mm (equivalent to 35mm)" means that the focal length of this camera is 8-24mm, and the diagonal viewing angle is equivalent to 38- 1 15mm of the traditional 35mm camera. Generally speaking, the standard lens focal length of a 35mm camera is about 28-70mm, so if the focal length is higher than 70mm, it means that the telescopic effect is supported. If it is less than 28mm, it means that it has wide-angle shooting ability. Hyperfocal distance is the distance from the center of the lens to the focal point. The focal length of a lens is divided into image focal length and object focal length. The focal length of an image is the distance from the main surface of the image to the focal point of the image, and the focal length of an object is the distance from the main surface of the object to the focal point of the object.

fundamental principle

Determine the main plane and focal length: When the incident parallel light (or its extension line) intersects with the emergent convergent light (or its extension line), the main plane of refraction can be determined, and the intersection of this imaginary plane and the optical axis of the lens is the main point. The distance between the main point of the image and the focal plane (focal point) formed by infinite light is called the focal length of the compound lens (strictly speaking, the effective focal length). The same principle can also be used to determine the main surface and focal length of an object. Hyperfocal distance refers to the distance from the center of the lens to the focus, usually in millimeters. The camera lens projects the light in the shooting scene onto the film or sensor. Visible field of view (FOV) is determined by the horizontal and vertical distance of the scene covered by the lens. Large sensors and films have larger FOV and can record more information in the scene. The focal length and FOV are usually based on 35mm film, because this format (35mm) is commonly used.

In 35mm photography, a lens with a focal length of 50mm is called a "standard lens" because the shooting scene is neither enlarged nor reduced, and the shooting range is the same as that seen by the naked eye (the image angle is 46).

hyperfocal distance

Wide-angle lens (short focal length) can make the camera "see wider" because its imaging angle is larger; The telephoto lens (long focal length) can make the camera "see farther", but the visual range is narrower. The following are descriptions of focal lengths corresponding to some typical lenses: By adjusting the hyperfocal distance, photographers can choose to shoot at a shorter distance or a longer distance to get different perspective feelings. Some digital cameras will have barrel distortion at the wide-angle end and pin pad distortion at the telephoto end.

35mm equivalent focal length

Because the sensor of digital camera is smaller than the area of 35mm film, digital camera engineers introduced the concept of "equivalent focal length" to convert the focal length of digital camera lens into an equivalent focal length of 35mm, which is convenient for photographers to study.

focal distance

Before adjusting the hyperfocal distance, please confirm whether one shot is empty or all shots are empty. If all the lenses are empty, you need to adjust the potentiometer of the lens lifting motor. If only one lens is empty, please adjust it according to the following steps:

1. Press the up or down key of the transmission keyboard to select the lens to be adjusted.

Second, press the SHIFT key to move the cursor to the TR column, enter 987, and then press VALID to display the following: lens 50 ing comp 04284 TURR. Adj 0 1788。

a/mf0c 1 PROC/speed 0 trpp ROV 480

3. The value after 3.RINGCOMP is the focal length of the lens, and the unit of this value is1%mm. Modifying this value will change the focal length of the lens. For example, change 04284 to 04384.

4. Press the effective key after modification, indicating that the machine will give an alarm and display: DATAERROR.

Press the PAGE key to view TR, enter the correct paper feed length here, and then press the VODIL key.

5. Take a photo to see if the focal length is true or false.

6. Repeat steps 2 to 5 until the focal length is adjusted.

Manual focus adjustment: Auto focus is usually used, but in special circumstances, such as barbed wire, glass, objects moving between targets and so on. Often the focus of the picture will be blurred, because DV will judge the distance and then adjust the focal length according to the signal reflected by the object in front when using the autofocus function, so as long as the autofocus is switched to manual and the focal length is locked on the object you want to shoot, the focal length will not change. As different brands of DV display and adjust in different ways, please refer to the instruction manual for adjustment.

Basic definition

Hyperfocal distance of camera lens is a very important index of lens. The focal length of the lens determines the imaging size of the object on the imaging medium (film or CCD, etc.). ), which is equivalent to the proportion of objects and images. When shooting the same subject at the same distance, the image with long lens focal length is large, and the image with short lens focal length is small. According to different uses, the focal length of camera lens varies greatly, from a few millimeters to a dozen millimeters to several meters. The viewing angle of a standard lens is about 50 degrees, which is the viewing angle that a person can see with one eye without turning his head and eyes. The feeling observed from the standard lens is basically the same as the scenery we usually see. The standard lens focal length of a 35mm camera is mostly 40mm, 50mm or 55mm. The focal length of the standard lens of 120 camera is generally 80mm or 75 mm. The larger the camera frame, the greater the focal length of the standard lens. However, due to the size of imaging medium (CCD or CMOS) of digital camera, the focal length of standard lens is also inconsistent. In order to facilitate direct perception, when talking about DC lens, the so-called equivalent focal length of 35mm camera is often used, and this equivalence refers to the equivalence in viewing angle. Only the lens of 35mm camera can be compared with other cameras and digital cameras. Wide-angle lens, as its name implies, has a wide shooting angle and is suitable for shooting scenes with short distance and large range. Sometimes it is used to deliberately exaggerate the foreground performance, with a strong sense of distance and perspective. A typical wide-angle lens of a 35mm camera has a focal length of 28mm and a viewing angle of 72 degrees. Commonly used are the so-called small wide angles of 35mm and 38mm, which are slightly longer than 28mm (more common in fool machines). Compared with the so-called fisheye lens, the super wide-angle lens (for example, the focal length is 24mm and the viewing angle is 84 degrees) has a focal length of 8mm and the viewing angle can reach 180 degrees. Long-focus lens is suitable for shooting distant view, with small depth of field, easy to blur the background and highlight the subject. The long focal length lens of a 35mm camera is usually divided into three levels. The lens below 135mm is called medium focal length, such as 85mm, 28-degree viewing angle, 105mm viewing angle, 23-degree viewing angle and 135mm viewing angle. Medium focal length lens is often used to shoot portraits, sometimes called portrait lens. 135-500 is called long focal length, such as 200mm, viewing angle 12 degrees, 400mm, and viewing angle of 6 degrees. More than 500mm is called ultra-long focal length, and the viewing angle is less than 5 degrees, which is suitable for shooting distant view. For example, the close-up on the court and the shooting of wild animals, because it is impossible to get close to the subject, the ultra-long focal length lens is of great use.

Focal distance classification

The focal length of a lens is divided into image focal length and object focal length. The focal length of an image is the distance from the main surface of the image to the focal point of the image, and the focal length of an object is the distance from the main surface of the object to the focal point of the object. It must be noted that the focal length of the object and the focal length of the image are not necessarily equal, because the telescope structure is widely used in camera lens design, especially zoom lens. What we usually call the focal length of the camera lens refers to the focal length of the image. How to determine the principal plane and focal length: When the incident parallel light (or its extension line) intersects with the emergent convergent light (or its extension line), the principal plane of refraction can be determined, and the intersection of this imaginary plane and the optical axis of the lens is the principal point. The distance between the main point of the image and the focal plane (focal point) formed by infinite light is called the focal length of the compound lens (strictly speaking, the effective focal length). The same principle can also be used to determine the main surface and focal length of an object.

Depending on the design, the position of the main surface may appear outside the lens. This is very important on many occasions. For example, for an 8mm fisheye lens, the main plane of the image should be 8mm in front of the focal plane, but the thickness of the reflector, exposure window and focal plane shutter can't be accommodated within 8 mm, so the 8 mm fisheye lens actually adopts the design of adding a negative optical system in front (also called inverted telescopic structure), so that the lens can be installed on the fuselage with the positioning distance of the image plane much greater than 8 mm.

focal distance

Similarly, if it is a 500mm super telephoto lens, if the telescope structure is not used, the length of the lens will exceed 500mm, which is undoubtedly very inconvenient to use. The design of the telescope structure can make the main surface far in front of the lens and greatly shorten the lens length.

When it comes to focal length, you can't help but talk about the zoom lens. The zoom lens consists of a fixed lens group and a variable lens group. By moving the variable lens group and changing the imaging optical path, the focal length of the lens can be changed in a certain range, thus changing the shooting angle.

The magnification of a long zoom lens refers to the ratio of the maximum focal length at the telephoto end to the minimum focal length at the wide-angle end.

Zoom lens is very convenient for shooting and framing because of its variable viewing angle, which is deeply loved by ordinary photographers. However, due to the complex structure of zoom lens and many relative moving optical elements, the consistency of imaging quality, resolution and distortion of each focal length segment can not be guaranteed in optical design. Therefore, the overall imaging quality of the zoom lens is difficult to reach a higher level. Especially the zoom lens with large zoom ratio is more difficult to obtain higher image quality.

Basic relationship

Therefore, at the same technical level, the imaging quality of zoom lens is lower than that of fixed focus lens, and the imaging quality of large magnification zoom lens is lower than that of small magnification zoom lens.

In the case of FC (for example, a 35mm camera), a fixed-focus lens is often used for high-quality photography, and even if a zoom lens is used, the zoom ratio is not large. However, in the case of DC, because the imaging area of CCD is relatively small, the geometric dimensions (focal length and lens diameter) of its zoom lens are also small, so it is easier to realize large zoom magnification in optical design.

How to understand hyperfocal distance?

When the lens is focused at infinity, the nearest limit of the depth of field near the camera is called hyperfocal distance. When the lens is focused on the hyperfocal distance with a certain aperture, the depth of field ranges from 1/2 to infinity. Hyperfocal distance is the fastest way to get the maximum depth of field or control the clear range of an image.

For a lens with a Jing Shenbiao scale, it is very simple to determine the hyperfocal distance: just focus on infinity, and then you can see the depth of field range from infinity to a point close to the camera indicated by the used aperture from the Jing Shenbiao of the lens. The distance from the camera to the depth of field is hyperfocal distance;

However, not all lenses have Jing Shenbiao, and the depth of field obtained by hyperfocal distance will change due to the lens focal length, aperture value and your setting of image definition. Therefore, "fuzzy circle" is introduced into the calculation of depth of field and hyperfocal distance as a factor of clarity. A' fuzzy circle' is the diameter of a real light spot that cannot be distinguished by human eyes. In fact, no one can distinguish a point with a diameter less than 0. In the photo with a distance of 25 cm 1 mm. This 0.l mm diameter takes its reciprocal, that is,11,which is equal to10 per mm, and can be used as the starting point to distinguish the number of lines per mm. ..

The formula for calculating the hyperfocal distance of a specific fuzzy circle is:

H=F2/Cf Here, H is the hyperfocal distance, F is the focal length of the lens, C is the blur circle, and F is the aperture used.

In normal use, the diameter of the fuzzy circle is generally set to 0.05 mm, thus simplifying the above formula to H= 1000F/f, and we can accurately know the hyperfocal distance used by any lens combination with focal length and aperture only by simple oral calculation. If we use a 50 mm lens with f/ 16 aperture, then substitute the above formula and calculate it in millimeters. The result is 50000/ 16 = 3 125mm, which means its hyperfocal distance is just over 3m.

Now that we have mastered the above calculation method, we can easily calculate the depth of field under any conditions through the following simple formula.

Depth of field near limit =HD/H+D Depth of field foreground = HD/h-d.

Here, h is hyperfocal distance and d is the focus distance. With this information, we can ensure sufficient depth of field before and after the object by arranging the object in the right position.

In the schematic diagram of this paper, the focus of the above picture is on 3 meters, which is hyperfocal distance. At this time, the near limit of the depth of field is1.5m, and the far limit of the scene is infinite. The following picture focuses on L.5m, and hyperfocal distance is still 3m. At this time, the near limit of the depth of field is 1m, and the far limit of the scene is 3m. This legend can limit the clear area to a group of people by shifting the focus from hyperfocal distance to half its distance, so that some scenes are arranged outside the depth of field.

Depth of field and hyperfocal distance (I) Principle and calculation of depth of field.

1, focus

When parallel rays enter the convex lens, the ideal lens gathers all rays at one point, which is called the focal point, and the distance from the focal point to the optical center of the lens is called the focal length. After the focal point, the light continues to diverge in a cone shape.

How to understand hyperfocal distance?

2. Nuclear fusion cycle.

Diffuse circle, fuzzy circle and so on.

Before and after focusing, the light from convergence to diffusion, the image of a point from a circle to a point (focus), and then spread to a circle. The circles before and after this focus are called diffusion circles.

How to understand hyperfocal distance?

If the circle is small enough, the naked eye can still be regarded as an image of a point. This acceptable maximum diameter is called the allowable confusion circle.

Watching the captured image is observed in a certain way. The image perceived by human eyes has a great relationship with the viewing distance. If the diameter of the diffusion circle is smaller than the resolution of human eyes, human eyes will feel clearly. At this time, the size of dispersion circle is called allowable dispersion circle.

The smallest object that human eyes can distinguish at an apparent distance (30cm in front of eyes) is about 0. 125mm. When establishing the standard, Datong Company selected the commonly used 7-inch photos (175× 125mm) as the basis of calculation, and the required dispersion circle was only within 0. 125mm, which was about11730 of the diagonal length of the image. Therefore, the standard set by Datong Company is dispersion circle diameter δ =11730 diagonal length of negative film.

Different manufacturers and different membrane areas have different requirements for allowable dispersion circle diameter. The allowable dispersion circle of 35mm photographic lens varies from manufacturer to manufacturer (provided that the picture is enlarged to 5×7 inches and the observation distance is 25~30cm). Generally, the value range is about11000 ~11500 of the diagonal length of the film. It can be seen that the depth of field is relative, not absolute, and is directly related to the value of the diameter δ of the dispersion circle. At the same time, we can also see that the value of dispersion circle diameter δ is related to the technical ability of lens manufacturers.

Commonly used values are:

Draw a picture

24 mm× 36 mm

6 cm ×9 cm

4"×5"

Allowable dispersion circle diameter δ

0.035 mm

0.0817mm

0.146mm

3. Depth of field

When focusing, the lens will be clearly imaged on the focal plane, and the foreground and background of the focus will also be imaged on the focal plane. As long as the diffusion circle they image is equal to or smaller than the allowed diameter of the diffusion circle, we think it is clear, so that the image has a clear interval, which is the depth of field (below).

How to understand hyperfocal distance?

From the above, we can know that there is an allowable diffusion circle before and after the focus, and the distance between these two diffusion circles is called focal depth, which corresponds to the depth of field. The so-called depth of field means that there is a clear imaging range before and after the subject (focus), and the scenes in this range are imaged on the focal plane, all within the limited range of allowable dispersion circle.

The depth of field varies with the focal length, aperture value and focusing distance of the lens. Generally speaking:

1, short focal length, large depth of field,

Far focus, large depth of field,

Small aperture and large depth of field.

How to understand hyperfocal distance?

Based on the photographer, the clearance range from the focus point to the near point is called the foreground depth of field, and the clearance range from the focus point to the far point is called the back depth of field.

How to understand hyperfocal distance?

As can be seen from the formula, the back depth of field >: the foreground is deep.

It can be seen from the formula of depth of field that 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 by the size of the allowable dispersion circle). These factors affect the depth of field as follows:

(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 lens focal length, the smaller the depth of field; The shorter the focal length, the greater the depth of field;

(3) Shooting distance: The farther the distance, the greater the depth of field; The closer the distance, the smaller the depth of field.

5. Calculation example

①& lt； ? Xml: namespace prefix = st 1 />50 mm/f2.8.

②50 mm /f8

③ 105mm/f2.8

δ

0.035 mm

0.035 mm

0.035 mm

f

50 mm

50 mm

105mm

F

2.8

eight

2.8

L

3000 mm

3000 mm

3000 mm

δl 1

316mm

754 mm

78 mm

δL2

400 mm

1518mm

82 mm

δL

716mm

2272 mm

160mm

From the above table, we can roughly see the interaction among depth of field, focal length and aperture:

①50mm/f 2.8 lens, clear distance of 2.68m-3.40m and depth of field of 0.72M.

②50mm/f 8 lens with clear distance of 2.25m~4.52m and depth of field of 2.272M.

③ 105mm/f 2.8 lens with clear distance of 2.92m~3.08m and depth of field of 0. 16M m. ..

6. Jing Shenbiao

Using the formula of depth of field calculation, we can calculate a Jing Shenbiao for our daily photography (because the calculation is complicated, you can't calculate it on the spot for the time being), but some books also provide ready-made Jing Shenbiao. The following is the Jing Shenbiao provided in the book (this is provided by Nikon for Nico lens) for your reference.

How to understand hyperfocal distance?

Jing Shenbiao can be made into tables or in other ways. I made a dial depth of field scale on the lens of the camera in the usual way and calculated it. It is more convenient to use this scale than to check. You can download it (see the article "depth of field calculation disk"), print it out on thick paper, and nail a small nail in the middle to use it.

7. hyperfocal distance.

Definition: On the premise that the focal length and aperture of the photographic lens are determined, the photographic object distance that can obtain the maximum depth of field is called the focal length and the hyperfocal distance under the aperture.

The above is hyperfocal distance's definition, which seems a bit confusing. Besides, what's the use of hyperfocal distance? For clarity, I will use the depth of field marker above.

How to understand hyperfocal distance?

Figure 1: I believe this depth of field ruler can be understood at a glance: the current focus is 2M. You can see that there are two indicator lines on each side of different aperture values, which indicate the clear range of foreground and background when the aperture is 2M away. For example, if you use an aperture of F= 1 1, then the clear distance is about 1.5-3M.

Figure 2: This is the case where the lens is focused at infinity. If you shoot the scenery, you can see it clearly with the aperture F= 16, about 4.5M.

Figure 3: This focusing situation in Figure 2 is not the best, because the back depth of field is not used at this time.

If we focus on 4.5M, we can find that when the aperture is still F= 16, we use the back depth of field of F= 16:

The back depth of field indicates that the line pair is at infinity, so that focusing not only ensures the definition of infinity, but also the foreground depth of field refers to 2.2M, and the clear range is more than 2M in front of Figure 2, and the maximum depth of field is obtained.

This is the "hyperfocal distance" focusing method, and the focusing position of 4.5M is called hyperfocal distance.

Hyperfocal distance's method is often used in snapshots, because it is within my known range (for example, beyond 2.2M mentioned above), so there is no need to focus. You can grab time, capture shots, and ensure clarity at the same time. So reporters and the like are more popular.

The calculation of hyperfocal distance distance is complicated, so if your lens is attached with a depth scale, you can aim the back depth line of the selected aperture value at infinity when focusing, without calculation, which is very convenient to use. This is also a great application of the depth of field ratio in the lens.

Of course, when we don't have this ruler, we'd better use the Jing Shenbiao tool or rotate the depth ruler.

Hyperfocal distance is a common photographic method in landscape photography and documentary photography. Hyperfocal distance is a very practical concept related to depth of field.

When focusing on the subject, the scenes in front and behind the subject can form a relatively clear image on the film, so the sum of the front distance and the back distance is called the depth of field, where the front distance is called the foreground depth of field and the back distance is called the back depth of field. If the aperture of a lens is fixed, when the focus ring rotates from near to far, the front and back depth of field will increase, especially the back depth of field. In this way, when the focus ring rotates to a certain focus distance, the back boundary of the depth of field just extends to infinity, and the focus distance at this time is the hyperfocal distance of the lens under this optical ring. If the focus is farther away, the depth of field will decrease, because the depth of field at the back will not increase, but the front boundary of the depth of field will be far away with the distance from the focused object surface. So you can get the maximum depth of field by focusing on hyperfocal distance. So hyperfocal distance is also defined as the shooting distance where the maximum depth of field can be obtained. When focusing with hyperfocal distance, the front boundary of the depth of field is just at the distance of 1/2 hyperfocal distance. Obviously, in order to apply hyperfocal distance, you must remember the lens hyperfocal distance values under different aperture settings.

Hyperfocal distance's calculation can use empirical formula:

For example:

20mm lens @f/2.8, HD = 4.3m.

24mm lens @ f/2.8, HD = 6.2m

50mm lens @f/ 1.8, HD = 42m.

50mm lens @ f/5.6, HD =13.4m.

If you want to make the foreground and background clear and use as large an aperture as possible, where is the most suitable focus?

There is another formula:

2X (foreground distance x background distance)/(foreground distance+background distance)

For example:

The person being photographed is 0/0m away from the lens and the house behind is 22m away from the lens, so 2 * (10 * 22)/(10+22) = 13.75, that is, when the focal length is adjusted to1.

Adams provided hyperfocal distance formula in photography is:

H=F*F/(f*d)

F: lens focal length

F: aperture coefficient

D: the diameter of the fuzzy circle.

The blur circle of 0.05mm is too large for the resolution of lens and film that has been improved now. Generally, it is 0.03mm, which means 1/850 inches.

Hyperfocal distance is an effective method to replace AF in MF era. With the shortening of focal length, the contraction of aperture or the gradual widening of shooting distance, the depth of field gradually expands. The back depth of field expands much faster than the front depth of field! Soon, the depth of field behind expanded to infinity. It can be proved that the foreground depth at this time is exactly half of the focus distance. So from half the focus distance to infinity, it is within the depth of field. In other words, as long as the object is outside the focus distance of 1/2, there is no need to focus when shooting! Usually used for snapshots.

Auto-focus machine is inconvenient to use in hyperfocal distance, and even can't be used, because most of them don't display distance data, so it can't be confirmed. If you have to use it, you can only use it manually and adjust it according to the lens proportion. In addition, the telephoto lens hyperfocal distance is too far away. As far as the 200MM lens you use is concerned, the hyperfocal distance at 32 aperture is about 50m (135). According to the formula, the foreground depth is about 30m, and the scenery close to this distance is inevitably unclear. If the focus is within 50 meters, the foreground is out of the clear range. Therefore, if a large depth of field is generally required, the focal length of the lens should not be too long (unless there is no important close-up that must be clear). In addition, the size of the dispersion circle in hyperfocal distance formula depends on the requirement of magnification of 6 times. If high magnification is needed, the diameter of the dispersion circle should be reduced accordingly, and the hyperfocal distance range is much narrower. An enlarged picture of more than one meter, shot completely according to hyperfocal distance's formula, will not have a clear foreground and background.

If it is a fixed-focus lens, remember the hyperfocal distance value under different apertures or ordinary apertures. When shooting, there are two options for the focus position:

1. If you choose the goal of infinity, you will know that the range of infinity to hyperfocal distance is clear, but it wastes hyperfocal distance.

2. Select an object near hyperfocal distance to focus, and then move the focus through AF-Lock. At this time, the hunger in hyperfocal distance is half to infinity.

If the focus is selected between 1 and 2, it is a bit wasteful; If the focus is near 2, infinity is unclear.

Windows version of depth of field calculator that can be downloaded on the Internet: software name f_Calc 1. 14 Chinese version.