The traditional SLR camera is called 135 camera, also called 35 mm camera. Why?

135 camera refers to a 35mm camera, and its name comes from the film width of 35mm. In order to unify the standards of cameras, Kodak has formulated the standard of 1XX name.

135 film uses 35mm film, and 35 is its width. So, what about the previous 1? The Leica camera designed by oskar barnack first used 35mm film, but at first, the film had to be put into the reusable contact, and the title had to be cut before shooting. 1934, Kodak introduced the disposable 135 film box, which was actually an invention of nagel camera factory in Stuttgart, Germany, and Kodak bought the factory. Kodak officially launched 1935 Kodak color film. Therefore, 1 of 135 refers to one-off combination which is different from reusable combination. The complete definition of 135 film is "35mm film with one-off combination".

120 camera is named after using 120 film. "120" is the product number of a kind of film and has no special significance.

The lens focal length of 120 camera is different from that of 135 camera. Take 6 x 6 as an example: the standard mirror is 80mm, which is equal to 50mm of 135 camera. 50mm of 6 x 6 is equal to 28mm of 135 camera, and 645 150mm is equal to 90mm of 135 camera. 120 film is also called brownie film, or B2-8 film. It uses 120 film, which has a larger area and a width of about 6 cm. Different models of 120 cameras use different film lengths, which are 4.5, 6, 7, 9, 12 or even 17 cm, so there are 645 and 66 120 cameras.