What is Focal length?
{{refimprove|Date=November 2017}} The '''focal length''' tells how strongly a [[Lens (optics)|lens]], a curved [[mirror]] or another [[optics|optical]] device brings [[light]] together or spreads it out. If rays of light go straight into a lens and the focal length is positive, the focal length is the distance to the point behind the lens where the rays will be brought to a focus. If the focal length of the lens is negative, the focal length is the distance at which the light has spread to twice its original size. Light from a large distance produces an image at F (focal point). The distance from the centre of the lens to F is the focal length. {{Photography}} {{sci-stub}} [[Category:Optics]] [[Category:Photography]]