Security cameras are one of the most important tools in the protection of facilities and critical assets. However, the phrase, “What you see is what you get” applies … literally. Proper setup of surveillance cameras is directly related to the level of effectiveness they will provide. One essential aspect of setting up a security camera is its field of view (FOV).
Webster’s would tell you that a camera’s field of view is the angle between two rays passing through the perspective center of a camera lens to the two opposite sides of the format. It can be further defined as having a vertical component (vertical field of view) and a horizontal component (horizontal field of view). In layman’s terms, that means it’s the image you see from the camera in either the live or recorded view. That sounds easy enough, but there are several mistakes that you should take care to avoid.
The FOV concept can be deceptively straightforward, such that often not a lot of forethought is put into it. However, as you take the time to further analyze its relationship to other aspects of the perimeter design, the security objectives and even the camera itself, it quickly becomes evident this is a crucial aspect of the total design and something that needs to be determined early on in the process. Read on to discover mistakes commonly experienced in the field, and use the information as a guide to avoid these types of issues in future deployments.
1. Not Doing Your Homework
One of the first things to realize is FOV is not an independent variable. As outlined in “8 Points to a Securer Perimeter,” camera layout can be an expensive proposition, and it is even more expensive when done wrong. You need to consider that pole placement, detection scene, blind zones and FOV are dependent variables. Changing one impacts the others. The existence of the variable focus lens has often caused the attention to this dependency to be overlooked, with the idea that camera misalignments or scene issues can be accounted for by later adjustment of the variable focus feature of the lens. This is a mistake and a potentially costly gamble.
You should go into your design considering each aspect, including a fixed FOV, and its dependency on the other setup variables. Brush up on your geometry, find and use a FOV calculator and a good camera layout tool. Make sure you verify your detection scenes, overlap your camera coverage for blind zones and define your FOV settings so you have some wiggle room after the equipment is installed. There will be inaccuracies in pole placements and unforeseen scene issues, but you shouldn’t count on a varifocal lens adjustment to be able to accommodate.
2. Thinking Like a Photographer
We all remember our high school photography class and the rule of thirds: two-thirds of the scene should be ground and subject; one-third should be reserved for the sky. We never seem to get it right when we’re taking photos of Aunt Beatrice or our vacation photos from Hawaii, but it’s amazing how many times we get it right when setting up security cameras. Although the rule of thirds is pleasant to the viewer’s eyes, in the security world, it does not apply.
There is almost no security application where viewing the sky has any value. However, there are many reasons why you should not look at the sky. These include items such as glare and blinding the camera during sunrise and sunset. Another consideration is the idea that you are essentially wasting 33% of your video storage and network bandwidth on the interesting cloud formations. The only reason to have sky in your FOV is to give a point of reference and ensure you have enough room for any vertical detection zones.
As a general rule, 10% of the scene is more than enough to give a frame of reference. When considering vertical detection scenes, for example ensuring you can monitor for intrusions that come over a fence, even less view of the sky is required.
3. Going to Bed Too Early
Jobsite walks are an extremely valuable part of the security design process. Good consultants and educated site owners make these available to potential security bidders so all the unique aspects of the site are understood in the early planning phases of a security design. I’m sure you or your company has participated in many of these, but I’d be curious how many have been through a nighttime site walk. Most times these are thought as unnecessary, as a security design will typically include some type of consideration for low light viewing: infrared (IR) illuminators, thermal cameras, etc.
However, there are many sources of existing light that need to be considered when setting a FOV: existing facility lights, periodic headlights, lights from adjacent facilities, sunrise/sunset, reflective light (water, windows), etc. Light sources can play havoc on cameras in a variety of ways, so it’s important to know where they are and to plan your FOV around them if possible. Unfortunately, if you don’t plan on staying up for the nightshift, you won’t have the opportunity to explore where these lighting issues might be lurking.
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Video Surveillance ·
Eric Olson ·
Field of View ·
Perimeter Security ·
Puretech Systems ·
Video Surveillance ·