Each lens has specific details inscribed on its name plate that give information about how it will perform. The most important information will read something like “1:1.8 f=45mm” (which could also be written “45mm F1.8,” depending on the manufacturer). These are the two fundamental parameters of a lens.
The number specified in mm is the focal length. This gives us an idea of the angle of view (AOV), as shorter lengths give wider angles. Here the focal length is 45mm.
The other set of numbers refer to the maximum aperture of the lens. 1:1.8 indicates that the maximum aperture is f/1.8. This is useful as we can tell how fast the lens is.
Lenses will also carry the manufacturer or brand name and possibly its individual serial number. There may also be information about the type of coating and the number of elements and groups in the lens. If the lens has a thread for accessories, the size may be given with the diameter symbol ø and a number specified in millimeters.
