What is aperture?
By Steve Lowry 2018-06-29 3182 0
Function of aperture
Aperture can be adjusted to control the amount of light to sensitive surface from the lens into the body of camera, which is as a great important index for the camera and within the lens in common. Its size will regulate the amount of light entering into the light-sensitive components through the lens.
Species of Apertures
1. Fixed aperture:
The simplest camera has a fixed aperture with only one hole—Walter Houser Aperture.
2. Variable aperture:
Only a series of different sizes of circular holes arranged around the disc with a central axis; the rotation of the disc can move the appropriate size of circular hole on the optical axis to achieve the effect of control aperture. In the middle of 19s century, John Walter Houser invented this aperture.
3. Cat-Eye Aperture:
It is separated from two components by a thin metal sheet with oval or diamond-shaped holes in its centrality, making the two thin metal sheets with semi-elliptical or semi-diamond-shaped holes opposing arranged and relative movement can form the Cat-Eye Aperture that is commonly employed for simple cameras.
4. Iris-type aperture:
It is composed of multiple overlapping arc thin metal leaves that can change the diameter of the central circular holes by its separation and reunion. Some cameras can change the aperture diameters in virtue of rotating the ring on the lens barrel, while others change the aperture diameter by the usage of a microprocessor chip to control micro motor automatically. The arc thin metal leaves can be up to as many as 18 pieces. The more arc thin metal leaves, the closer that the hole approaches to circular shape. Designing the shape of thin metal sheet by the electronic computer, it may use only 6 thin metal leaves to achieve near circular aperture.
5. Instantaneous aperture:
SLR camera aperture is instantaneous aperture; the aperture switches to the preset size only when the moment that the shutter is open. Usually the aperture is in full position.
6. Shutter-type aperture:
The aperture on some simple cameras is with the shutter function for both, most of these shutter-type aperture are dual-leaf Cat-Eye aperture where the difference from simple Cat-Eye aperture is the shutter-type aperture is complete closed usually. When the shutter button is pressed down, dual-leaf aperture switches to the preset aperture diameter keeping this aperture diameter after a preset period to shutter opening and then the aperture is closed immediately. As a result, the aperture is with the shutter function.
Specification of aperture: F-number
It is the ratio of focal length to effective aperture diameter (the reciprocal of the relative aperture). For example, for the 50mm standard lens, the maximum light admitted diameter is 29.5mm that the calculated value of the maximum aperture is 50mm/29.5mm=F1.7, thus, it can be understood that the same zoom lens at different focal length, the maximum aperture is different after conversion although the maximum light admitted diameter is the same. The larger the F-number, the smaller the aperture is, inversely, the smaller the F-number, the larger the aperture is.
The complete ranges of F-number are as follows:
F1, F1.4, F2, F2.8, F4, F5.6, F8, F11, F16, F22, F32, F44, F64. Every two blocks that the amount of light travelling is with a difference of double. For example, the aperture from F4 to F2.8 adjusted, the amount of light will be double added, from F2.8 to F2 that double added again. Thus the F-number to actual aperture is inverse, the aperture is F1 when the maximum amount of light travelling and the minimum is F64. For 135 cameras, the minimum aperture for most lenses is F22.
At present, the lens in mobile phone field can be achieved that the maximum aperture is F1.8 that is the mainstream for large aperture standard in digital camera field as well and the effect of brighter photos and delicate life. A small number of mobile phone put to use F1.8 aperture that giving priority to domestic products such as Vivo, Lenovo and other models.
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