Almost every camera uses a converging lens. Since that type of lens refracts light towards the focal point, an image produced at that spot would be in focus. The camera is designed so that the distance between the lens and the film is the exact same as the focal distance of the lens. This allows for clearer pictures. However, this would only work for objects at a certain specific distance away. By zooming in or out on the camera, we are increasing or decreasing the focal length. This allows us to adjust the focus depending on the object’s distance. Another way to change the focus of the camera is to adjust the aperture. The aperture is the opening between the lens and the body of the camera that allows light to pass through. If the aperture grows, then the amount of light that enters the camera will grow as well. It is controlled by the diaphragm, which is a mechanical piece of the camera that can increase or decrease the aperture.
The process that a camera goes through in order to capture an image is relatively simple. When the shutter button is pressed, the shutter opens, allowing rays of light from the object to pass through the lens. Said light would refract onto the film, producing a real, smaller, inverted image. When exposed to the light, the film would then store the image onto it. After a brief moment the shutter would return to its closed state, not allowing more light to enter the body of the camera. That is how a picture is captured onto film. These days, a light sensitive device such as a charge-coupled device replaces the film. This device captures the image and stores it on a digital storage, where it could be accessed via computer.
In order to give the user an idea on how their picture would look, they can look through the viewfinder on their camera. But how can it replicate the real image that will be made on the film? Well, the viewfinder in the camera uses a mirror, a translucent screen, and a pentaprism in order to do so. First, the light would travel through the converging lens, and would hit a mirror that is in front of the shutter and the film. The mirror in question is slanted, so the ray of light would be reflected at a 90-degree angle. Then it would pass through a translucent screen where an inverted image is produced. The light passing through the image would then enter the pentaprism, where it would hit the inside wall at an angle greater than the critical angle, so the ray of light would be reflected to another surface in the pentaprism. It is then reflected again due to total internal reflection. Next, he ray of light passes through the inner wall parallel to the viewfinder eyepiece. Since it reaches the inner wall at an angle of 0-degrees, it passes right through. The two reflections that occurred within the prism flipped the image so that it would appear right side up to the user, showing them exactly how the image would look like. In conclusion, that is how the viewfinder displays a real image identical to the one that would appear on the film.