Photography is full of fancy terms and complicated science, but we are here to explain it all to you in simpler terms. Today we are focusing on focal length. This term gets thrown around often, especially when looking at lenses, so it’s important you get familiarized with it.
What is focal length?
Focal length is the distance between a camera sensor and a lens’ point of convergence.
Put simply, focal length is the distance between a camera sensor (or film) and a lens’ point of convergence.
The hardest part is understanding what the point of convergence (also known as optical center) is. When light rays enter a lens they travel through glass and bend to converge in a single point. This point is where light data is collected to form a sharp image for the sensor to record. Manufacturers measure the focal length focused to infinity, to keep a standard.
Focal length is measured in millimeters. A 50mm lens will have a point of convergence that is 50mm (or 5cm) from the sensor.
In the graph below, the point of convergence is marked with “F’”, while the focal length is noted …read more
Source:: android authority