When you finally set out to select your Surveillance Camera, for realizing your well thought out Home Security project, you should be advised that, besides other elements equally important, the lens plays a determining part in the camera performance.

It is the lens that determines the amount of light entering the camera. Besides the quality of materials and of manufacturing, usually reflected in the price, some of the lens characteristics have much bearing on the viewed picture.

Even if you do not want to become an expert in lenses, there are a few concepts that you should understand before you purchase your surveillance camera.

The subjects are well known from the field of still photography, so that the principles should not be completely unfamiliar for whoever has some practice of family picture taking even at a very basic level.

In most surveillance cameras, lenses are interchangeable. Therefore you should decide if the picture seen on the monitor is satisfactory for your application, with reference to the depth of focus, the angle of view and the amount of detail you want to distinguish.

In case you are not satisfied with the performance of the standard lens supplied, you should ask to see how a different lens would improve the images you want to observe.

Normally one should select the best overall picture for the purpose. Note that by changing one of the characteristics (i.e. aperture) one modifies other related properties (i.e. the depth of focus).

The overall result is a matter of compromise whereby, by sacrificing somewhat one feature one gains a better response from another one.

Fixed focal length is a common selection: although limiting somewhat the dimension of the space where all objects result clearly perceived (depth of focus), it simplifies the mechanical construction and reduces the price.

You may be familiar with autofocus feature found in modern digital cameras. There is no comparable capability in cameras because they must work unattended. A lens whose focal length can be manually adjusted is called a Varifocal lens but should not normally be considered for surveillance purposes.

Equally too sophisticated for the application would be a motorized zoom lens, capable of being commanded from a distance to select the preferred level of detail between wide-angle and telephoto.

Fixed iris or aperture is another characteristic to be considered that simplifies construction and operation, albeit with some compromise on picture quality. It would probably be easier to provide sufficient illumination then going for more complex optics.

In conclusion, despite the nice and costly alternatives available, for a simple home surveillance system it would be advisable to select one of the simplest lenses, provided that the quality of the picture is sufficient for the intended purpose.

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Elia Levi is a retired engineer. He built a website to assist with a step-by-step Guide to understand, design, select and set up, all by yourself the best and least expensive surveillance system for your home security. Read more on the subject of this article at http://www.1st-diy-home-surveillance-guide.com/Surveillance-camera-lenses.html

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