Three elements of exposure

The three elements of exposure are: shutter, aperture and sensitivity.

Shutter:

Shutter, alias shutter, shutter, is a device used in camera equipment to control the time when light irradiates the photosensitive element, which is located in the camera body or lens. The unit of shutter speed is "seconds", and the exposure of two adjacent shutter speeds is twice different. The highest shutter speed of professional 135 cameras reaches116000 seconds.

Common shutter speeds are: 1, 1/2, 1/4, 1/8,1/5, 1/30,/kloc-0. The types of shutters include front mirror shutter, inter-mirror shutter, aperture shutter, rear mirror shutter, mirror shutter, focal plane shutter, mechanical shutter and electromagnetic shutter.

The purpose is that the brightness of the scene is different, and the shutter time can be adjusted accordingly to make the film properly exposed; Shooting a moving object has a short shutter time to freeze the image of the object; When used under special circumstances, it can be opened for a long time.

Aperture:

Aperture is a device used to control the amount of light entering the photosensitive surface of the fuselage through the lens, usually in the lens. The aperture size is expressed by f value. For the manufactured lens, the diameter of the lens cannot be changed at will.

However, the luminous flux of the lens can be controlled by adding a polygon or circular aperture grating with variable area inside the lens. This device is called an aperture. Simply put, the grating with variable aperture in front of the camera lens is called aperture.

Sensitivity:

Sensitivity, also known as ISO value, is a measure of the sensitivity of negative film to light, which is determined by the measurement of sensitivity and several values, and has recently been standardized by the International Organization for Standardization. For the negative with low sensitivity, it takes a long exposure time to achieve the same imaging effect as the negative with high sensitivity, so it is usually called slow negative.

Highly sensitive negatives are therefore called fast negatives. Whether it is digital or negative photography, in order to reduce the exposure time, the relative use of higher sensitivity usually leads to the decline of image quality (due to thicker negative particles or higher image noise or other factors).