Focal length of the distance in millimeters (mm) from the center of the lens should be the focal point in this film (SLR) or sensor (DSLR) for emphasis.
Field of view (FOV) is the point of view is measured in vertical (portrait) and horizontal (landscape), the amount of film or sensor, the greater will be the point of view can be recorded. Please visit this site in English for this and other schemes.
Since there are many styles and sizes of the sensor or film, FOV is measured most often in the horizontal (diagonal), and the most popular and most often compared (link) is a 35 mm focal length (industrial fish-eye 16 mm) wide-angle focal length in comparison with more advanced (eg, 200 mm telephoto).
In the world of photography, 35 mm, 50 mm focal length is calculated as the standard by which people have about the same angle (at 46 °) diagrams to explain the other side. Below is an example of the difference between the focal length of two.
10.5mm Fisheye DX: wide viewing angle.
