That mark is called a focal plane mark. The focal plane mark on a camera is a small symbol or line that indicates the exact location of the camera’s sensor or film plane within the camera body. It is typically located on the top or side of the camera body near the lens mount.
The purpose of the focal plane mark is to help photographers determine the precise distance between the camera and the subject they are photographing. This is important because different lenses have different focal lengths, and the focal length affects the distance at which the lens will focus sharply.
By knowing the distance from the focal plane to the subject, photographers can ensure that their images are in sharp focus where it matters most. This is particularly important when using wide aperture settings (like f/1.4 or f/2.8), which can create a very shallow depth of field and require precise focusing to achieve sharpness in the right areas of the image.
To use the focal plane mark for determining hyperfocal distance, the photographer can use a hyperfocal distance chart or calculator. These resources will provide the necessary information based on the camera’s sensor size, aperture, and focal length to find the hyperfocal distance.
Once the hyperfocal distance is determined, the photographer can adjust their focus manually to align the focal plane mark with the hyperfocal distance on the lens barrel. This will ensure that the maximum depth of field is achieved and the resulting image will be sharp throughout the scene.
Additionally, the focal plane mark can also be used for aligning the camera with a nodal point when shooting panoramas. This will help prevent parallax errors and ensure that the resulting panorama will be seamless and free of distortion.
Simple, right?