When shooting portraits, we often want to separate the portrait from the background. A shallow depth of field can achieve this goal, so we need to shoot with a large aperture.

When shooting scenery, we want to get clear photos both far and near, so we need a deep depth of field, and we need to shoot with a small aperture.

Types of visor

Fixed visor

The simplest camera has only a fixed aperture with a round hole-the Waterhauser aperture. The original variable aperture was just a series of circular holes of different sizes arranged around a disk with a central axis; rotating the disk can move the appropriate size of the circular hole to the optical axis to achieve the effect of controlling the aperture. In the middle of the nineteenth century, John Waterhouser invented this kind of aperture.

Mobile phones often use fixed shading rings

cat's eye aperture

The 　　 cat-eye diaphragm is composed of a sheet of metal with an oval or diamond-shaped hole in the center, and two sheets of metal with a semi-elliptical or semi-diamond-shaped hole are aligned and moved relative to each other to form a cat-eye diaphragm.

cat-eye hood is mostly used for simple cameras.

The 　　"iris" type aperture is composed of a plurality of overlapping arc-shaped thin metal blades. The clutch of the blades can change the size of the central circular aperture. Some cameras can change the size of the aperture by turning the ring on the lens barrel, while some cameras use a microprocessor chip to control a micro-motor to automatically change the aperture of the aperture. There can be as many as 18 curved thin metal blades. The more arc-shaped thin metal blades, the closer the aperture is to circular. By designing the shape of the thin metal blades by the computer, only 6 thin metal blades can be used to obtain a nearly circular aperture.

instantaneous aperture

The aperture of a SLR camera is an instantaneous aperture, and only when the shutter is opened, the aperture is reduced to a predetermined size. Usually the time circle is in the largest position.

SLR lens uses this kind of

and shutter aperture

Some simple cameras have an aperture that also functions as a shutter. Most of these dual-blade cat-eye apertures are different from simple cat-eye apertures: the shutter aperture is usually completely closed.

Large and medium format cameras are mostly inter-lens shutter

At the moment when the shutter is pressed, the double-blade aperture opens to a predetermined aperture, and after maintaining this aperture for a predetermined shutter opening time, it closes immediately: in this way, the aperture doubles as a shutter.