Is it better to have a small focal length or a large focal length?

Focal length (focal length)

Focal length is a measurement of the concentration or divergence of light in an optical system. It refers to the distance from the center of the lens to the focus where the light is gathered. It is also the distance from the center of the lens to the imaging plane such as the film or CCD in a camera. Optical systems with short focal lengths have a better ability to gather light than optical systems with long focal lengths. Simply put, the focal length is the distance from the focal point to the apex of the mirror.

If you have seen "f=" in the English specification book of the camera, then the number following it is usually its focal length. , that is, the focal length. For example, "f=8-24mm, 38-115mm (35mm equivalent)" means that the focal length of this camera is 8-24mm, and the diagonal angle of view is equivalent to the focal length of 38-115mm of a traditional 35mm camera. Generally speaking, the standard focal length of a 35mm camera lens is about 28-70mm, so if the focal length is higher than 70mm, it means it supports telephoto effects, and if it is lower than 28mm, it means it has wide-angle shooting capabilities.

The "focusable range" is an extension of the focal length, which is usually divided into general shooting distance and close-up distance. The general shooting distance of the camera is usually marked as "from a certain centimeter to infinity", and further Products with high-end designs often provide close-range shooting functions (macro) to make up for the inability to focus in general shooting modes. Some cameras place great emphasis on the magical ability to support 1 cm close-up shots, which are suitable for shooting fine objects.

The camera lens is a set of lenses. When parallel light rays pass through the lens, they will converge to a point. This point is called the focus. The distance from the focus to the center of the lens is called the focal length. A lens with a fixed focal length is a fixed focus lens; a lens with an adjustable focal length is a zoom lens.

When a beam of parallel light passes through the convex lens with the main axis of the convex lens, it will be converged by the convex lens into a point on the other side of the convex lens. This point is called the focus. The distance from the focus to the optical center of the convex lens is called this The focal length of a convex lens. A convex lens has a focus on each side.

Optical center: The center of the convex lens can be approximately regarded as the optical center.

The camera lens we use is equivalent to a convex lens. The film (or the photosensitive device of a digital camera) is near the focus of the convex lens. In other words, the distance between the film and the optical center of the convex lens is as large as Approximately equal to the focal length of this convex lens.

Convex lenses can form images. Generally, when a convex lens is used as a camera lens, the clearest image it produces will generally not fall exactly on the focus, or in other words, the distance from the clearest image to the optical center (image distance) is generally not equal to the focal length, but slightly greater than the focal length. The specific distance is related to the distance between the object being photographed and the lens (object distance). The larger the object distance, the smaller the image distance (but in fact it is always greater than the focal length).

Because when we take pictures, the distance between the object being photographed and the camera (lens) is not always the same. For example, when taking pictures of people, sometimes, if you want to take a picture of the whole body, just stay far away, and if you want to take a picture of the half body, As close as you can get. In other words, the image distance is not always fixed. In this way, if you want to get a clear image, you must change the distance from the film to the optical center of the lens as the object distance differs. This changing process is what we usually call "adjustment". Burnt".

The focal length must be appropriate! ! ! ! !