Lens Terminology Sharing: What Is Aperture?
In the fields of photography and optics, aperture is a very important concept. It is a device inside the lens used to control the amount of light passing through. Simply put, the aperture is like the pupil of the human eye; it can adjust its size according to the intensity of ambient light, thereby controlling the amount of light entering the eye.
Aperture is one of the core concepts for beginners in photography, and in this article, we will explore its definition and function.
1.Definition of aperture
(1)Effective caliber
The diameter of the light beam when parallel light rays from an infinitely distant source pass through the front lens of a camera is called the lens caliber. This actually represents the basic light-gathering capacity of the lens and is therefore called the effective caliber.
The larger the ratio of lens diameter to lens focal length, the larger the diameter and the stronger the light sensitivity; conversely, the smaller the ratio, the weaker the light sensitivity.
(2)Relative caliber
Relative caliber refers to the light-gathering ability of a lens after being adjusted by the aperture mechanism. The relative caliber is variable; it is the ratio of the beam diameter after stopping down the aperture to the focal length. In this case, the effective caliber represents the maximum light-gathering diameter of the lens.
The aperture is composed of several curved, lightweight metal blades, which can be adjusted to increase or decrease the diameter of the light opening within a certain range.
2.Aperture scale
The aperture scale is what is commonly referred to as the f-number or aperture ratio, in the format "f/number". If the f-number is 8, it means that the diameter of the light beam at this relative caliber is 1/8 of the lens's focal length, usually written as f/8 or aperture 8.
The typical aperture scale for cameras is: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, where 1.4 represents the effective caliber, and the values from 2 onwards represent relative calibers.
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| Aperture scale display |
3.The function of the aperture
(1)Control the amount of light entering
The larger the aperture (the larger the diameter of the opening), the more light enters per unit of time, and vice versa. This characteristic directly affects the exposure of the photograph: under the same lighting conditions, a larger aperture will result in a brighter photograph, while a smaller aperture may result in a darker photograph.
(2)Adjust the depth of field
A smaller aperture produces a greater depth of field, resulting in sharper focus from near to far objects; a larger aperture produces a shallower depth of field, blurring the background and making the subject stand out more.
(3)Improve aberration
Stopping down the aperture can improve the image quality of a lens. The center of the image is sharp, while the surrounding or edge areas have poorer image quality, which can easily lead to image distortion.
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| Stopping down the aperture can improve the image quality of a lens |
(4)Adjust resolution
Resolution refers to a lens's ability to distinguish between parallel lines of equal width and spacing. Besides being related to the quality of the lens itself, resolution is also related to the size of the aperture. The larger the aperture, the higher the resolution, and vice versa.
In practical use, most cameras have an optimal aperture, usually around f/5.6. When the aperture is widened further, the resolution decreases. From the perspective of maximizing resolution, the ideal aperture setting for shooting is f/5.6 or f/8, while the ideal aperture for enlarging photos is f/5.6.
(5)Adjust contrast
The aperture can also change the contrast of the image; generally, a smaller aperture results in higher contrast, while a larger aperture results in lower contrast, which is especially noticeable when shooting on cloudy days.
4.The coordination between the aperture and other parameters
The aperture is one of the three elements of exposure (aperture, shutter speed, and ISO), and all three must work together to achieve correct exposure:
(1)If the lighting is dim, you can use a wide aperture (e.g., f/2.8), a slower shutter speed (e.g., 1/30s), and a low ISO (e.g., 100);
(2)If the light is strong, you can narrow the aperture (e.g., f/16), increase the shutter speed (e.g., 1/1000s), and use a low ISO to avoid overexposure.
The coordination between the aperture and other parameters
5.Applications of aperture
For high-quality, high-precision lenses, the aperture size does not significantly affect image quality; even at the widest aperture, it's generally difficult to discern any quality issues in the photos. However, for ordinary lenses, this effect is more pronounced.
The main manifestation is a decrease in image sharpness at the edges of the photograph when using a larger aperture, and some may even exhibit image distortion. This is because the lens itself is of lower quality, suffering from aberrations and chromatic aberration, and these shortcomings become fully apparent when using a large aperture.
6.Aperture selection for different scenarios
(1)Portrait photography: Commonly uses a large aperture (f/1.4-f/4) to blur the background and emphasize the subject;
(2)Landscape photography: Typically uses a small aperture (f/8-f/16) to ensure everything from the foreground to the background is in sharp focus;
(3)Night scene/low light photography: Use a large aperture (f/2.8 and larger) to reduce ISO and avoid image noise;
(4)Macro photography: A large aperture can blur cluttered backgrounds, but attention must be paid to focus accuracy (shallow depth of field may cause the subject to be blurry).
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| Shooting options for different scenarios |
In summary, aperture is an indispensable part of photography, directly affecting the exposure, depth of field, and image quality of a photograph. Understanding the principles and applications of aperture can help photographers better control exposure and capture accurately exposed and ideal images under different lighting conditions.
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