Insight into Camera Specifications

Insight into Camera Specifications

The main criteria of a camera’s performance are its sensitivity and resolution. Secondary considerations are color or monochrome and indoor or outdoor suitability.

Sensitivity is the camera’s ability to respond to light levels. Resolution defines the amount of picture detail in the image produced by the camera.

Camera Resolution

This is expressed as the number of television lines that the camera is capable of producing. For example a basic bullet camera may have a resolution of 420TVL.

Cameras with much higher resolution have become more affordable in recent times, with small dome cameras now offering 1000TVL resolution.

IP Cameras (Internet Protocol) offer resolutions of 720p(1280 x 720) and 1080p (1920 x 1080). They are connected to recorder by CAT5 or CAT6 network cables.

The latest format is HD-Turbo or HD-TVI. These cameras offer 1080p resolution but the images can be sent over standard coaxial cable.

Whichever type and resolution of camera chosen it must be matched to suitable recorder.

Indoor/Outdoor Cameras

If a camera is to be sited outside and is not going to be mounted in an enclosure it must be classed as weather resistant.

The cable entry points are sealed and most bullet cameras come with trailing leads that allows the connections to be made inside the building. Typically 18inches (~45cm) should be sufficient. One bullet camera under review had only a few centimeters of cable. This means the connection would be exposed to the elements. Needless to say this model did not meet the selection criteria of Cliqenect.

The strength and durability of the casing is difficult to quantify but we have rejected cameras with flimsy plastic enclosures, particularly wireless cameras where the antenna dish looks like it could be easily damaged.

Light Levelslow_light

Choosing the correct camera to operate in ambient light conditions is possibly the most important although most tricky specification to understand.

cctv_cameraLight levels are usually measured in Lux. This is a measure of the light energy arriving on an area 1 meter squared of surface per second.

Typical Light Levels are:

Full Summer Sunlight: 50,000 Lux
Dull Daylight: 10,000 Lux
Shop/Office environment: 500 Lux
Dawn/Dusk: 1 – 10 Lux
Main Street Lighting: 30 Lux
Side Street Lighting: 0.5 – 3 Lux

The golden rule when deciding which camera to use for a given lighting condition is not to choose one that will only just give a picture. Try to give the camera approximately 10 times its quoted minimum scene illumination. Most cameras will be able to cope with excess light. The major problem is when they do not have enough light to produce a picture.

The sensitivity of covert cameras with pin-hole lenses are often quoted as 0.1Lux @f1.4. This seems to indicate that the camera will work in ¼ moonlight. Actually the pin-hole lens will have an aperture ratio of something like f4 and so the camera will need approximately 1 Lux to produce a picture.pin_hole

Unless your house is directly under main-street lighting the light level is probably less than 1 Lux at the front and even lower at the back. Bright security flood lights in theory help but often produce dark shadows a short distance from the house.

A monochrome camera rated at 0.05 Lux will produce reasonable results. Color needs a little more. However, color cameras achieve good night-time vision by switching to a monochrome mode. You will never get good night-time color pictures without huge amounts of additional lighting. So think carefully about the added cost of color over monochrome cameras. As most people are used to color television it sets a standard so it is very common to still select a color camera knowing it will switch to monochrome mode at night.

Monochrome cameras respond well to additional IR (infra red) lighting. With this in mind true night-vision cameras include a ring of IR LEDs. Color cameras also offer IR illumination but as stated previously will switch to monochrome at night even with the IR LEDs turned on. These are true night-vision cameras and are rate at 0 Lux.