Film cameras, which are traditional cameras, are divided into monocular cameras and binocular cameras. Film cameras only use negatives. Therefore, in terms of cost, consumers need to buy negatives, develop them into photos, and also need to develop negatives and photographic paper. Calculate the cost of each roll of film, about 60 yuan, if it is a positive film, about 40 yuan.

There is not much difference in working principle between digital camera and film camera. Both of them form an object image on the focal plane through the lens.