What is called the focal length: a) collecting lens; b) a diffusing lens?

The focal length of a converging lens is the distance from its main focus to its optical center. The focal length of a diffusing lens is the distance from its main focus to its optical center, taken with a “-” sign.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.