Fixed Focal Length and Variable Focal Length

1- Fixed Focal Length:

This type of lens is sometimes called a monofocal lens. As the name implies, it is specified when the precise field of view is fixed and will not need to be varied when using the system. The angle of view can be obtained from the supplier’s specification.






2- Variable Focal Length:

This is a design of lens that has a limited range of manual focal length adjustment. It is strictly not a zoom lens because it has quite a short focal length. They are usually used in internal situations where a more precise adjustment of the scene in view is required which may fall between two standard lenses. They are also useful where for a small extra cost one lens may be specified for all the cameras in a system. This saves much installation time and the cost of return visits to change lenses if the views are not quite right. For companies involved in many small to medium sized internal installations such as retail shops and offices this can save on stock holding. It makes the standardization of systems and costing much easier.