With the aperture, the photographer not only controls the amount of light that hits the sensor, but also the depth of the focused area. In addition there is a reduction of the image errors, but this is not an issue.
Different spellings
Apart from optical components, a lens also has complex mechanical constructions. An important element for the photographer is the aperture. The aperture is an aperture within the lens that can be varied in diameter by the user.
Iris levels
The size of the opening angle is determined by opening or closing. The larger the angle, the more light from the object to the image plane, the smaller it is, the less light. The control of the aperture opening is realized by means of sliding slats.
Impact on the image
The more complex the aperture is, the better the aperture corresponds to a circle. The exact diameter of the diaphragm in millimeters is less interesting for the photographer, since this information is always related to the focal length. Therefore, the information is given as a relative diaphragm aperture, ie, the ratio of the diaphragm aperture to the focal length. The effective diameter of the aperture divided by the focal distance is the same as the number 1 to the f-number. If the f-number is set to 4 on the lens, the aperture is 1/4 of the focal length.
Light intensity
It is also important: the larger the f-number, the smaller the aperture, the smaller the f-number, the larger the aperture. The spelling changes depending on the manufacturer or the environment. For example, the expression is found as a ratio or as a fraction, where the focal length is either equated to 1 or is represented by "f" (abbreviation for focal length). For example, the following notation is given for a diaphragm opening with 1/4 of the focal length: 1: 4, f: 4, 1/4, f / 4 or also briefly F4.
In principle, the designers could define the stages in which the user can adjust the aperture. In order to make it easier for the photographer, an international blind line was standardized. For aperture 1, the aperture is as large as the focal length. Each further stage corresponds to a halving of the amount of light that transmits the lens.
Now you have to pay attention: in the calculation of a circular area, the radius goes to the square, so the halving of the radius does not mean the halving of the area, but the reduction to a quarter. The normalized aperture row therefore always builds with steps of 1.4, which corresponds to the square root of 2. Two steps then again correspond to the square of 1.4 - ie 2. Two examples: The jump from aperture 4 to 5.6 corresponds to a step (4 x root (2) = 5,6), a jump of aperture 4 8 two levels (4 x 2 = 8).
The choice of aperture has various consequences. The primary is the regulation of the amount of light which contributes to the formation of the image. If the shutter is opened, more light hits the sensor. Thus, the exposure is controlled in combination of exposure time and sensitivity. A large aperture opening also allows for low-light shooting.
However, the relative diaphragm aperture also has an influence on the resulting image. The smaller the f-number, the larger the opening and the smaller the depth of the sharpening. For designing with the sharpness, it is therefore interesting that the aperture can be opened as far as possible. However, the imaging performance of the lens and the occurrence of imaging errors are also strongly dependent on the selected aperture.
The light intensity of a lens describes the maximum aperture compared to the focal length. This is the smallest adjustable f-number. For the photographer, it is usually interesting to use a lens that is as light as possible. Due to the connection between the f-number and focal length, a larger light intensity is also associated with a larger lens construction. The larger the focal length, the larger the lens must be to be light, which makes the lens large, heavy and expensive.
Buying advice: Buying a lens - what you need to know
If the focal length is varied with a zoom lens, the maximum aperture is often the same, so it must be accepted that the light intensity of a zoom lens decreases with increasing focal length. For example, most compact cameras and many compact lenses have a much lower light intensity in the telephoto position than in the wide-angle position.
Fading reduces the amount of light, but increases the sharpening depth. The sharpening depth is the area which is perceived as "sharp" by the observer. The ideal focus is only on a very narrow plane. Depending on the aperture, the focal length, and the tolerance permitted by the sensor and viewing condition, an area in front of and behind the focal plane is also perceived as sharp.
Sharpening depth
By controlling the diaphragm, this range can be reduced or enlarged. Since it is important for a bright viewfinder image or a low-noise preview on the display that as much light as possible passes through the lens, the shutter is usually closed by the camera for recording.
Guide: How modern lenses work
During viewing through the viewfinder or on the display, the aperture is opened. Since the diaphragm has a strong influence on the depth of the sharpening, many cameras have a dimmer button. Pressing the button closes the aperture to the adjusted working aperture, and the depth of the sharpening can now be judged. In the case of optical viewfinders, however, the viewfinder image is also significantly darker. Here, electronic viewfinders are clearly beneficial as the image is brightened by readjustment.
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