3vr P-Series SmartRecorder, Руководство по установке

Страница: 60 / 69

60
3VR SmartRecorder Installation and Configuration Guide
Example: A potential entry point offers 2 appropriate mounting positions, one at 12 feet away, the other at 24
feet away. In this case, the furthest mounting location is most appropriate.
Camera/Lens Specifications:
Cameras designated for face-based recording must comply with a wide range of specifications, primary among
them is the use of high-resolution cameras, (480 TVL or greater). The camera and lens must be appropriate to the
scene lighting conditions. For example, black & white low-lux or day/night camera for poorly lit areas, and super-
dynamic cameras where severe backlighting can occur.
An appropriate 4’ wide field of view, (FoV), is the result of the focal length of the lens in relation to the object dis -
tance from the camera. While an appropriate “fixed focal length” lens can be utilized, a VariFocal Lens is strongly rec -
ommended because the selectable focal length range enables a flexible field-adjustment (fine-tuning) capability.
VariFocal Lenses are available with manual or automatic iris features. The automatic iris format is used in applica -
tions where lighting conditions may vary, for example, areas exposed to daytime sunlight.
Lens Selection:
Typical VariFocal Lenses fall within the following approximate ranges; 3 to 8 millimeters (mm), 3 to 12mm, 5 to
50mm, and 20 to 100mm. The most common and least expensive are the 3 to 8mm versions, although most
Face Capture applications will require the larger size VariFocal Lenses.
Rule-Of-Thumb for Determining Lens Focal Length:
A 4’ wide FoV requires 1.2mm per foot of distance from subject; a 4½’ wide FoV requires 1.1mm per foot.
Reference chart below:
FoV
Distance From Object / Focal Length Needed for a Camera With 1/3” CCD
10’ 20’ 30’ 40’ 50’ 60’
4.0 ft. wide
12mm 24mm 36mm 48mm 60mm 72mm
4.5 ft. wide
11mm 22mm 33mm 44mm 55mm 66mm
In applications where a 4’ wide FoV is desired and the camera mounting location is 30’ from the subject, a 36mm
focal length is specified, and a 5 to 50mm VariFocal Lens is recommended.
Notes:
The above estimates assume the use of 1/3” CCD (the most common size) camera format. Results will vary in
applications using different size formats such as ½” or ¼”. Lens calculation tools are available from most camera
manufacturers, (online and pocket ‘slide-rule’ versions).
With megapixel cameras, deployment no longer requires such a large telephoto range when comparing to
analog and non-megapixel IP cameras. Evidently, this will depend on the particular application. Please refer to
the table in the Field of View section for determining the maximum width for each application.