Some time ago we issued guidelines for the identification of persons and vehicles. This is fine, but many system engineers were trying to find what camera and lens combination will satisfy these identification guidelines. And what about end users who know even less about camera and lens formats, how can they understand the competing specifications? This article all will be revealed for both groups.
In this Charts we will try to show the horizontal and vertical fields of view for many lenses and four formats are given in ‘The Principles of CCTV’ and were published in the first article CCTV. These charts also show the % of the screen height of a 5-6 feet person. The DVRMaster guidelines had not been published for general use.
The values for different degrees of identification are given as the percentage the 5 feet figure would occupy of the monitor screen. we call this the ‘screen height ratio’. The complete guidelines are provided in several DVRMaster articles and so only the basic ratios are given in this article.
These criteria are now becoming increasingly used as part of the specification for many CCTV and security camera systems. Usually the specification will state the distance from the camera for each criterion, sometimes the specification will ask the question, ‘at what distances from the camera will the criteria apply’? In either case it involves calculations that are not too difficult but can be tedious to keep repeating for each lens and camera location.
Another problem that many installer find difficulty in resolving are the different fields of view obtained from various camera and lenses sizes, i.e. what is the result of fitting a 1/3″ lens onto a 1/2″ camera, and how does this affect the screen height ratio at certain distances?
Here are some visual example for security camera field of view.