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[Concept]
English name for Aperture
The aperture is a used to control the light through the lens into the device of the photosensitive surface the amount of light in the body, is an extremely important indicator of the lens parameters, it is usually inside the lens.
In the lens inside a polygon or round, and the area of ??variable, in order to control the camera through the amount of light hole-like grating
Expression of the aperture size is the value of f.
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The original rationale
A junior high school physics class, which spoke of the imaging principle of the camera is the pinhole.
(2) the diameter of the holes is the number one focal length to aperture size.
For example, the standard lens 50/1.4 SLR camera, that is the lens focal length 50mm, aperture of the lens is 36mm, which is the focal length of a little quarter, known as the maximum aperture of the lens is 1.4.
Lens a few pieces of steel, the diameter of the holes smaller, changed to 8mm, in accordance with 8 in addition to 50 is equal to 16 one, that is, when the aperture 16.
Pinhole imaging experiments in the physics class know the holes the smaller, the more clear imaging.
Shoot landscapes, we have the aperture set to 11 or 16, so that the distance of the scene are clear.
Portraits, aperture into 1.4, in order to make the figures clear, while the background is blurred.
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[Type]
Aperture value series as follows: F1.0, F1.4, F2.0, F2.8, F4.0, F5.6, F8.0, F11, F16, F22, F32, F45, F64
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A fixed aperture
The most simple camera is only one hole of the fixed aperture - aperture Waters Hou se.
Initial iris is just a series of different-size hole arranged around a central axis of the disc;
Rotating disc can be moved to the appropriate size of the hole on the optical axis, to control the aperture effect.
Mid-nineteenth century, John Waters Hou se invention the aperture.
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[Cat's Eye aperture]
Style cat's eye aperture by a center oval or diamond-shaped holes, the foil is divided into two composed of two semi-oval or semi-diamond-shaped hole in the sheet metal on the row, the relative movement can form a cat's eye diaphragm. Cat's Eye diaphragm used for a simple camera.
The aperture of the iris type is composed of multiple overlapping curved thin metal blade, blade clutch can change the size of the center of the circular aperture.
Some cameras can make use of the rotating ring on the lens barrel to change the size of the aperture, and some camera is a microprocessor chip to control the aperture automatically change the aperture of the micro-motor.
Curved thin metal blades can be up to 18. Curved thin metal blade is more, the aperture is more nearly circular.
Computer design the shape of the thin metal blade, used only six thin metal leaf, nearly circular aperture.
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Instantaneous aperture
SLR camera's aperture is the instantaneous aperture, only the moment of shutter release, aperture reduced to a predetermined size.
Usually aperture at maximum position.
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[Chief shutter aperture]
Simple camera aperture both the functionality of the shutter, such Chief shutter aperture most of the pairs of leaves of the cat's eye aperture, and with a simple cat's eye aperture:
Chief shutter aperture is usually completely closed;
The moment you press the shutter, dual-blade aperture opens to a predetermined aperture to maintain the aperture to a predetermined period of the shutter opening time, and immediately closed;
As a result, the aperture in turn Chief shutter function.
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【Small】
Expression aperture size F value
(2) the diameter of the aperture F = lens focal length / lens aperture
(3) than the short focal length lens of long focal length lens aperture diameter.
4 aperture F value of the smaller, the larger the aperture (as shown), the amount of light in the same unit of time will be more, but on the level into the amount of light is exactly twice the next level.
For example, adjust the aperture from F8 to F5.6, will more than double the amount of light, said aperture big one.
F5.6 amount of light through F8 twice. Similarly, F2 F8 luminous flux of 16 times, F2, F8 to adjust the aperture opening of the four.
5 for the consumer digital camera, the aperture value of f is often the range of f2.8 - f16.
6 In addition, many digital cameras in the adjustment of the aperture, you can do 1/3 adjustment.
F behind the smaller the value, the larger the aperture, the amount of light is more;
F behind the greater the value, the smaller the aperture:
Simply say, in the same shutter, the larger the aperture, the more the amount of light, brighter screen; the smaller the aperture, the screen is dark.
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[For use]
Its size determines how much of the light into the sensor through the lens
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1, change the shutter speed]
Generally, exposure of the camera under the same sensitivity is determined by the aperture size (aperture F value) and shutter speed.
In the previous article, we know the diameter of the aperture F = lens focal length / lens diameter, that is the aperture smaller the F value, the greater the aperture, the greater the amount of light.
So we can reduce the shutter speed by increasing the aperture to increase the shutter speed, or narrow the aperture.
Large aperture lens is usually a very good performance in low light environments, called "The Mirror of the Night," a series of lenses in the field of SLR cameras.
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2, blur the background]
Addition can change the shutter speed, the aperture, as well as change the function of the depth of field. First of all, we come to know the concept of depth of field.
Depth of field: in front of the lens (and adjust the focus) has a certain length of space, when the subject is located in this space before and after the imaging is located just focus on the negatives of these two dispersion circle.
The length of the subject where this space is called depth of field.
In other words, the subject in this space, showing the image of the film surface ambiguity, within the limits allowed to diffuse round, the length of this space is the depth of field.
Simply put, the more shallow depth of field, bokeh is more obvious, the deeper the depth of field, background more clearly.
For example, we often see shooting flowers, insects, such as photos, background shot very fuzzy (called depth of field).
Shooting in the shooting of commemorative photos or group photos, scenic photos of the general will background have the same clarity as the subject (called depth of field).
Iris, lens, and the distance of the subject is an important factor affecting the depth of field:
(1) the larger the aperture the smaller the depth of field, aperture smaller the greater the depth of field.
(2) the longer the lens focal length the smaller, on the contrary greater depth of field depth of field.
The closer (3) the main body, the smaller the depth of field, the farther the main, the greater the depth of field.
In the same focal length, the larger the aperture, that is, the smaller the F value, the background blur effects are more obvious, the more shallow depth of field.
So you want to use the camera to shoot photos bokeh is the same focal lengths to make use of large aperture.
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3, the impact of image quality] DC
Theoretically the aperture size and camera focal clarity of the image is not related to, but not one hundred percent and matches the theoretical value due to the accuracy of the imaging principle of the optical lens and refraction of glass, so the image quality under different aperture or there is a certain differences.
Relative to the optical lens of the SLR camera, the DC lens aperture range to be much smaller, especially its smallest aperture value F8.0.
For the vast majority of DC in the camera's wide-angle side or the telephoto end, the maximum aperture (that is, F value of the minimum aperture) is the focus sharpness aperture, namely call The best aperture.
By the above resolution values ??in the laboratory as well as screenshots of real locations, we can find it.
Therefore, in addition to the landscape and need a larger depth of field photos, try to use a large aperture in the use of small DC to shoot shooting.
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4, the impact of image quality] DC
Relative to consumer digital camera, SLR camera lenses due to a more complex structure of the optical lens and a larger optical lens, the different size of the aperture SLR lens focal quality generally to a large number.
We are still laboratory shooting live shots to tell us.
Compared to the zoom lens, fixed focus lens design is more mature, optical structure is a lot simpler. The same focal lengths, aperture fixed focal length lenses were generally greater than the zoom lens aperture, and slightly better in the same aperture on the imaging quality.
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【Mode】
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Aperture and shutter priority]
Advanced more than a digital camera in addition to automatic (Auto) mode, there are usually
Aperture priority (Aperture Priority), Shutter Priority (Shutter Priority)
You can decide in some cases an aperture value or shutter value, then, respectively, with the appropriate shutter or aperture, to present the picture of the different depth of field (sharpness) or effect.
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Aperture Priority exposure]
Us first to decide the aperture value of f, the camera metering system according to the case of light at that time, automatically selects the appropriate shutter speed (for the precise stage shutter speed) to cope with.
Digital camera with the exposure mode dial, usually engraved with "A" for Aperture Priority Mode on a turntable. Aperture Priority mode is suitable for photographic attention to depth of field effect.
As the digital camera's focal length is much shorter than the focal length of the traditional camera, the lens aperture opening small, it is difficult to have a narrower depth of field.
Most digital cameras will have a special portrait exposure mode, use the built-in procedure enables the prospects and fuzzy after King.
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【Article is excerpted from: Baidu Encyclopedia】
【Network reprint / Just reference】
【Translation is by Goolge】
