How to describe it in photographic terms

Focus aperture shutter shutter speed depth of field preview sensitivity color temperature white balance exposure relative aperture exposure combination

Interpretation of photographic technical terms

The focal length is basically the distance from the center of the lens to the clear image formed on the film plane (other photosensitive materials).

The unit of focal length is usually expressed in mm (millimeter), and the focal length of a lens is usually marked in front of the lens, such as 50mm (this is what we usually call "standard lens", which refers to 35mm film), 28-70mm (our most commonly used lens), 70-2 10mm (telephoto lens) and so on.

A device used to control the amount of light passing through a lens. If you raise the aperture by one level, the amount of light entering the camera will double, and if you lower it by one level, the amount of light will be halved. The aperture size is expressed by F value. The order is as follows:

f/ 1，f/ 1.4，f/2，f/2.8，f/4，f/5.6，f/8，f/ 1，f/ 16，f/22，f/32，f/44，f/64

(The smaller the F value, the larger the aperture)

Shutter is a device used to control the exposure time. Shutters can generally be divided into mirror shutters and point curtain shutters (that is, steel shutters that people often say).

Shutter speed The time that the shutter opens. It refers to the time (exposure time) when light sweeps across the film. For example, "1/30" means that the exposure time is 1/30 seconds. Similarly, "1/60" means that the exposure time is1/60s, and the shutter of1/60s is1/30s. The rest and so on.

When the object in depth of field is clearly gathered, it is quite clear from a certain distance in front of the object to a certain distance behind it. The distance from front to back with a fairly clear focus is called depth of field.

Some points for attention about depth of field:

The smaller the aperture, the greater the depth of field. The larger the aperture, the smaller the depth of field.

For any aperture, the depth of field behind the focus is about twice that before the focus.

The shorter the focal length of the lens, the greater the depth of field; The longer the focal length of the lens, the smaller the depth of field.

Preview of Depth of Field Because when viewed through the viewfinder, in order to synthesize and collect as bright an image as possible, the lens always opens its aperture to the maximum, so the shallowest depth of field always appears at the maximum aperture. In order to see the actual depth of field, some cameras provide a preview button of depth of field. Press the button to reduce the aperture to the selected size, and the scene you see after shooting is the same as that recorded on the film (memory card).

Sensitivity indicates the photosensitive speed of photosensitive materials. The unit of sensitivity is "degree" or "fixed". For example, "ISO 100/2 1" means a film with a fixed sensitivity of 100/2 1. The higher the sensitivity, the more sensitive the film is (that is, the less light is needed to shoot the same photo normally in the same shooting environment, that is, a higher shutter or a smaller aperture can be used). The sensitivity of 200-degree film is twice that of 100-degree film, and that of 400-degree film is twice that of 200-degree film, and so on.

Color temperature Different pigments contained in different kinds of light are called "color temperature". The unit of color temperature is "K" (Kelvin). The color temperature we usually use is 5400 K-5600 K; The color temperatures that light types A and B can adapt to are 3400K and 3200K respectively. Therefore, different types of films should be selected according to the subject and environment, otherwise there will be color cast (unless the color temperature is corrected by color filter).

Attachment: Definition of color temperature "Suppose there is a black metal in an environment of minus 273 degrees (absolute zero). With the increase of temperature, black metal will emit light with different wavelengths, and the metal color temperature corresponding to colored light plus 273 is the color temperature of light. " For example, when a metal is heated to 2500 degrees Celsius, it will emit red light, and the color temperature of this red light is "2500+273" K, which means that the color temperature of this red light is 2773 K. The lower the color temperature, the higher the percentage of long-wavelength light (red and orange light). The higher the color temperature, the higher the percentage of short wavelength light (blue light and purple light). For example, the color temperature of sunlight at noon is about 5500K; The color temperature of the flash is about 5600K; The color temperature of the blue sky is around 20000K; 100 watt light bulb's light color temperature is about 2600K K.

Because of the different spectral characteristics of white balance under different lighting conditions, the photos taken are often biased, such as blue under fluorescent lamp and yellow under incandescent lamp. In order to eliminate or reduce this color shift, digital cameras and video cameras can adjust the color settings according to different lighting conditions, so that the color of photos is as undistorted as possible and the color can be restored to normal. Because this adjustment is often based on white, it is called white balance.

The process by which exposure light reaches the surface of the film to make the film sensitive. It should be noted that by exposure, we mean film exposure, which is a necessary process for us to obtain photos.

The ratio of the effective aperture (beam diameter) to the focal length of the relative aperture lens. The larger the relative aperture, the faster the lens speed. Such as 1:2.8, 1:3.5-4.5, etc. Among zoom lenses, lenses with fixed relative aperture are generally called professional lenses, lenses with fixed relative aperture but between 1:2.8- 1:4 are called quasi-professional lenses, and the rest are called mass lenses.

Exposure combination means that different combinations of aperture and shutter can be used in the same shooting environment. For example, the shutter measured by the exposure meter is 1/30 seconds, and the aperture should be 5.6, so F5.6 and 1/30 seconds are an exposure combination. We can also use the exposure combination of F4 and 1/60 seconds instead, and we can also use the exposure combination of F2.8 and1125 seconds instead. In other words, these combinations are equivalent. However, it should be noted that although these exposure combinations are equivalent, that is to say, the exposure is accurate, but the depth of field obtained by different combinations is different.