What is the concept of focal length? What is the concept of focal length in photography?

1, focal length, is a measure of light convergence or divergence in an optical system, which refers to the distance from the optical center of the lens to the focal point of light convergence when parallel light is incident. An optical system with a short focal length has a better ability to collect light than an optical system with a long focal length.

2. Simply put, the focal length is the distance from the focal point to the center of the mirror. Focal distance f and image distance

3. Focal length refers to the change range of focal length of zoom lens. The division of lens focal length: the first is the meter head, which is the so-called standard lens. Its viewing angle is about 43 degrees, and the viewing angle of the photo is closest to the human eye.

4. Different film frames have different focal lengths of titles. The standard lens of 135 is about 50mm, the focal length of the 6×6 title of 120 is 80mm, and the title of 300d is about 50 ÷1.5 = 33 mm. ..

5. Generally, the 50mm and 28-70mm marked on the lens refer to the focal length of the lens. Common focal lengths are 8mm, 15mm, 24mm, 28mm, 35mm, 50mm, 85mm, 105mm, 135mm, 200mm, 400mm, etc.

The field of view of the lens is generally marked according to the standard of 35mm. According to different visual fields, the lens can be divided into standard lens (50mm), wide-angle lens (24mm) and telescope head (500mm).