The diaphragm is the element that is responsible for controlling the passage of light in a camera, it is located inside the objective or lens. It is formed by a series of blades that open or close, which are what allow the passage of light to be regulated.
The aperture of a camera is also known as the f number and it indicates the brightness of the lens it incorporates. The famous f-numbers correspond to the degree of aperture of the diaphragm. Taking this into account a small number will correspond to a very large opening while a large number will correspond to a very small opening.
The diaphragm of a photographic camera in addition to controlling the passage of light is also responsible for controlling the depth of field. Depth of field is the area that is in focus within a photograph and is completely related to aperture measurements. The smaller the number the smaller the depth and the higher the number the greater the depth. If we open the diaphragm all the way, light will enter through most of the diameter of the front lens, making us only see a part in focus. But if we close it, the useful surface of the lens will be smaller, making the planes of sharpness increase.
Regardless of the type of objective we have, several problems related to the opening may appear. When we open it to the maximum, black edges will appear in the photographs. When we close it to the maximum when the light passes through such a small space it will be distorted and lose sharpness.
This is why it is recommended to achieve optimal photo quality and avoid problems, take shots with intermediate apertures.