Why can photos taken with digital cameras be displayed quickly?

For a long time after the invention of the camera, the photos we took could not be seen immediately.

Because the camera uses a plastic sheet called "film", the film is coated with a photosensitive chemical, which will change chemically and become different substances after being irradiated by light. People put the film into the camera, and the light reflected by natural objects can shine on the corresponding position of the film through the lens, which makes the photosensitive chemicals change chemically, thus taking good photos.

Because we usually need light to see things, and the film will continue to be exposed as soon as it meets light, completely destroying the photos just taken. Therefore, the film that takes a good photo must be processed in a dark room, and the film is soaked in different chemical liquids in turn, so that the chemical substances on the film are no longer sensitive to light after chemical reaction, so that the image on the film can be fixed and the photo can be developed.

However, after the invention of digital cameras, everything changed. The photos taken one second can be seen the next. Why? There is a photosensitive element in a digital camera, which is installed in the position where the film is exposed in a traditional camera. This photosensitive element consists of thousands of electronic photosensitive units that can capture photons. When we take pictures, each photosensitive unit will record the color and brightness of the scene light at the corresponding position.

The information recorded by all units is summarized, processed by the processor inside the digital camera and stored in the file of the memory card, which becomes the digital photo we can see. The biggest advantage of digital cameras is that they can be repeatedly exposed. So the design of digital camera is very different from that of film camera.

Digital cameras can take pictures in real time. Because the photosensitive element of a digital camera can be repeatedly exposed, framing, photometry and exposure can all be completed by using the photosensitive element. However, the film in the film camera can not complete the task of framing and metering, so framing and metering need to be completed through complex optical components and additional electronic components. Digital cameras can also play back instantly.

The digital camera processes the signal of the photosensitive element through the processor in the camera, so we can immediately see the photo just taken on the LCD screen behind the camera. If it's not good, we can take a new photo right away. Although the digital camera has only one photosensitive element, it can be repeatedly exposed, and it is no problem to take hundreds of photos continuously, while the film camera must change the film if it wants to take dozens of photos.

Summary: Film cameras have a history of nearly 200 years, and there are still many traces of film cameras in the digital cameras we use now. For example, in the digital SLR camera we use, the reflector, mechanical curtain shutter, pentaprism, phase focusing and other components were originally designed for film cameras. Some of these designs will disappear from digital cameras in the process of technological development, and some may remain for some time.