An Introduction to Focal Length in Photography: Angle of View, Magnification, and Prime/Zoom Lenses
Explains focal length, angle of view, magnification, and the basic differences between primes and zoom lenses based on Nikon photography tutorials; does not claim to prove perspective geometry, crop equivalence, or cross-frame equivalence.
What does focal length represent?
Focal length, usually expressed in millimeters, is the basic parameter for describing a photographic lens; Nikon's definition indicates that it is not the actual length of the outside of the lens, but a description of the optical distance when focusing to infinity. 〔G-FL-01〕
How does focal length change the viewing range?
In the basic explanation of the Nikon tutorial, focal length is related to the angle of view and the degree of magnification of picture elements: a longer focal length, a narrower angle of view, and a higher magnification rate; a shorter focal length, a wider angle of view, and a lower magnification rate. What is explained here is the change in framing, and does not deduce the shooting distance, perspective or pixel details after cropping. 〔G-FL-02〕
Fixed focus lens and zoom lens
Prime lenses provide a fixed focal length, while zoom lenses vary within their stated focal length range. Nikon summarizes the convenience of zoom lenses to adapt to different themes and viewing angles, while prime lenses are fixed at a single focal length; please check the information of each model for specific lens weight, aperture and image quality. 〔G-FL-03〕
Pay attention to the frame and context when reading focal length examples
The Nikon tutorial lists FX approximately 14–35mm and DX approximately 10–24mm as examples of wide-angle lenses, and lists common scenes such as architecture, landscapes, indoors, and narrow spaces. This is Nikon's approximate classification reference, not a hard boundary that all systems adhere to. 〔G-FL-04〕
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