We are pleased to offer free access to the Online lens calculator developed by Constant Consulting.
There are many methods of calculating the field of view needed for a
particular application and the appropriate lens selection. Previous
articles in CCTV Today have covered this topic in depth. Probably the
most useful method is to make a video recording using a camera and zoom
lens from a hydraulic hoist at the actual camera positions being
proposed. Many companies now offer a service using a custom designed
vehicle with several types of camera mounted on hydraulic masts. Inside
the vehicle are various switching and recording devices. However, they
can only cover a limited number of surveys compared to the total number
of opportunities. This article looks at other ways of determining
fields of view and lens specifications.
There are several types of CCTV viewfinders which are like a
small telescope with a zoom lens. You look through the viewfinder and
adjust the lens until the required field of view is in the frame. The
lens focal length for various camera formats is then shown on scales on
the barrel. One problem is that some of these useful devices only
adjust to comparatively wide angles and are mainly suitable for
internal systems. Also they do not provide a permanent record of the
field of view ,which could lead to disputes in the future.
If you have a 35mm camera with a zoom lens, you can accomplish
two benefits at one go. First, find the correct lens angle for any
camera by reading the zoom setting when the required field of view is
composed through the camera viewfinder. Second, make a permanent record
of this by taking a shot, keeping a note of the shot and the zoom
setting.
The accompanying table lists the lens focal lengths and angles
for various zoom settings on a 35mm camera and the equivalent focal
lengths for camera formats.
_files/Table4.gif)
|
