How can a format of the camera and the focal length of a lens be determined?

Question

Quizplus · Accepted Answer

The format of the camera and the focal length of a lens can be determined by looking at the manufacturer's specifications. These specifications are usually listed on the camera or lens itself or can be found online. Using a formula or looking at the projected image may give an estimation, but the manufacturer's specifications will provide the most accurate information.

How Can a Format of the Camera and the Focal