Posts Tagged ‘ camera lens’



Surveillance Camera Lens

Written By:
Monday, July 11th, 2011

Surveillance camera lens are slowly beginning to evolve with the technology that supports them.  Before the digital age, a good majority of the surveillance cameras required that a lens be purchased for each camera.  Presently, some cameras still work that way, but the vast majority has the lens built right into the camera.  These lenses are often referred to as “board lenses.”

There are three major types of digital video camera based on their shape, the box type, the bullet type, and the dome type.  Basically the bullet and dome type cameras come with a lens already built into the unit.  This is often referred to as a board lens.  The box camera however, almost always requires the purchase of a lens.

As far as the lenses go, there are two different types of surveillance camera lenses, fixed and varifocal.  Fixed lenses do exactly what their name implies; they stay fixed in a certain immobile position.  Varifocal lenses have the ability to change their focal length either manually or remotely depending on the lens.

This means that for fixed lenses, the size of the field of view never changes; the lens can’t alter its own focal length so the width of the capture shot never changes.  This is great for use where there is no need to mess with changing the focal length regularly such as monitoring a parking lot, an entrance or exit, and other uses where zooming in on a subject or object is really not required and the camera will not be moved around a lot.

Varifocal lenses on the other hand, can move in and out changing the size of their focal length.  This is particularly handy when it is necessary to change the camera’s field of view to accommodate moving objects, tight shots, etc.  The focal length of a varifocal surveillance camera lens is normally expressed in millimeters (mm).  For example a fixed camera lens with a focal length of 3.0 mm will produce a fairly wide angle shot, whereas a focal length of 15.5mm will produce a narrow angle shot.

The nice thing about a varifocal lens is, depending on how it is made, you can get a focal length as small as possible and any focal length in between its maximum focal length.  It’s important to note that some of these varifocal lenses must be moved manually (by hand) while some our connected to a motor that drives the lens and is controlled remotely.

As long as we are on the topic of surveillance camera lenses, we’ll also mention a few of the characteristics of lenses that you probably should be aware of in addition to just focal length.  Four other points come to mind:  1. Depth of field; 2. F stop; 3. CS or C mount; and 4. Manual or Auto Iris.

Depth of Field

The depth of field is the distance from the camera to the object at which remains in focus.   Generally, the higher the F stop and tighter the Iris positions, the more objects that will be in focus.  In other words, a large Depth of Field means almost all objects in the Field of View can be in focus.  On the other hand, a small Depth of Field will only allow a small section of the Field of View in focus.

F Stop

The F stop is the foacl length divided by the effective aperture diameter.  In much simpler terms, the F Stop is an indication of the speed of the lens.  Since light must pass through the lens to the sensor, the F Stop gives us an idea of how much light it will absorb during the process.  A low F Stop lens is very efficient whereas a high F stop lens will require a lot of light.

CS or C mount

There are two standard surveillance camera lens mounts the “CS” and the “C.”  The difference between the C and CS is found in the distance between the lens and the CCD (Charged Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor).  The C mount distance is 17.5mm while the CS mount is 12.5mm.

Iris

The iris works with the surveillance camera lens to control the amount of light entering the camera via the sensor.  For cameras mounted in positions that have changing light sources, it is a good idea to use a lens with an automatic iris.  For cameras used inside or in environments where the light conditions seldom ever change, manual irises are sufficient.

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Dome Security Camera

Written By:
Friday, April 1st, 2011

The dome security camera is one of the most popular types of digital video security camera in use today.  Thanks to modern technological advances a lot of electronic power can be packaged inside a small 3.5 inch diameter dome camera.  Not only are they small and powerful, but the average dome security camera is light weight as well (in most cases weighing just under one pound), which makes it easy to mount just about anywhere.

Today, there are three standard types of digital video camera based on shape; the box type, bullet type, and dome security camera.  How, what, and where the camera is used usually dictates the type, although user preference is also a factor.

Dome cameras originated from their older analog ancestors.  These cameras were often big and bulky and required a great deal more depth than today’s dome security camera.  Often, the older cameras were actually box cameras placed behind a wall or ceiling with the body of the camera extending into the wall space ith just the lens extending through a pre-cut opening.   A glass dome was then fixed over the lens to make it more aesthetically pleasing.  Blackened glass or two-way mirror glass was often used to conceal the lens, so that potential shoplifters, intruders, etc. would not know in what direction the lens was aimed.

Current dome security cameras are nothing like what is described in the previous paragraph.  Considering that the main components of a digital video camera are the lens, the sensor chip, and the Integrated Circuit (IC) electronics the largest part of the camera is often the lens which on the average is about 3.6mm in diameter.

A digital video dome security camera is a compact, highly sophisticated electronic piece of equipment.   The sole purpose of the camera is to transfer light images into electronic images that can be seen on an electronic display device such as a monitor.

It does this by first using a lens to focus the field of view onto a tiny sensor chip.  These chips range from 1/3 inch to about 1/2 inch square.  One of two different sensor ships is used.  Although the chips go about the process differently, both yield the same result; transferring light into electronic impulses that can be measured (and therefore used to create an electronic image).

The sensor chips are either a Charged Coupled Device or CCD or a Complementary Metal Oxide Semiconductor or CMOS.  After the sensor chip converts the light image into an electronic impulse, the IC chips take over processing and digitizing the electronic information and passing it along to the Digital Video Recorder or DVR.

There are several types of dome security cameras based on how they function or where they are intended to be used.  Dome security cameras can be classified as indoor, outdoor, or indoor/outdoor types although most outdoor types today are the combination indoor/outdoor.  Indoor dome cameras are intended to be used inside, under protective cover from the weather and other elements.

Outdoor dome security cameras are protected by an outer shell or case that prevents water, snow, hail, or other damage to the camera itself.   These cameras are often rated according to the International Electrotechnical Commission’s (IEC’s) Ingress Protection or IP standard.   An IP rating of IP55 or higher is usually considered good.

Dome security cameras are usually flush mounted on a ceiling or wall, but may be mounted on special mounts that can range from peduncle type to horizontal extensions.  They require very little surface area for mounting, and can usually be mounted easily using from two to four screws.  The video transmission cable and the power supply cable usually attach from the underside of the mount or there are extensions exiting from under the mount such that the wires remain hidden and protected by the structure the camera is mounted on.

Dome security cameras may also work in InfraRed (IR) modes and the IR Light Emitting Diodes or LEDs are normally clustered right around the camera lens.   This provides directed IR illumination in the exact field of vision of the camera lens.

Security Camera King offers a wide selection of indoor and outdoor (as well as indoor/outdoor) dome security cameras.  Our cameras are of the highest quality and offer the best performance at the most economical price in the industry.

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