Posts Tagged ‘ varifocal lenses ’

Varifocal Camera

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Thursday, October 20th, 2011

Security cameras utilize two basic lens types based on focusing parameters.  These are called fixed lens cameras and varifocal cameras.  Fixed lenses have a “fixed” or constant, unchangeable focal length while varifocal lenses have a focal length that can vary. A more familiar term used for electric powered varifocal lenses is a “Zoom” lens; we will concentrate on the varifocal type in the following article.

In addition to the focusing characteristics of the lens, light requirements must also be considered.  The light that is allowed to penetrate through the lens and strike the electronic sensor chip is normally controlled by a mechanical device known as an “iris.”  The iris may be fixed, manual, or automatic.  This refers to how the iris makes the light opening, called the aperture, smaller or larger. The aperture is equivalent to the human eyeball’s pupil.  In very low light settings the aperture needs to be open wide to allow enough light to strike the sensor chip.  However, in bright light conditions, the aperture is very small to prevent too much light from flooding the sensor chip.

If a security camera is used indoors in a setting that has a constant intensity of adequate light (i.e., a store, a warehouse, or a well lit room), then a “Fixed Iris Lens” should perform adequately to serve your needs.  But if the actual field of view may need to change to a tight shot and back again, a varifocal camera is the answer.

In settings where the light conditions can vary from dark to bright (i.e., outside or a camera aimed at an outside window) an “Auto Iris Lens” will be needed to compensate and adjust for the varying light levels.

Finally, in light conditions that are constant for long periods of time but change from dark to light or light to dark, a “Manual Iris Lens” can be used.  These lenses’ apertures are changed by hand to provide the optimum light exposure.

Lenses are created using a combination of Fixed and Varifocal parameters with Fixed Iris, Auto Iris, or Manual Iris apertures.  Most security camera lenses’ focal lengths vary from 3.6 mm to 16 mm for fixed focal length lenses, to well over 70mm for varifocal cameras.  A short focal length will yield a wide angle of view and a long focal length will yield a narrow angle of view

The actual mathematical formula used to calculate the width and height of the area covered is Width = Camera Horizontal Format X Distance/Focal length and Height = Camera Vertical Format X Distance/Focal length.

In this formula, values for the Camera’s Horizontal and Vertical Format are the size of the CCD or CMOS chip expressed in MILLIMETERS, not inches, with the pictures aspect ratio of 4:3.  For example, for a 1/3 inch CMOS chip the vertical size of the chip in mm is 3.7 mm and the horizontal size is 4.9 mm.  Use the vertical format value of 3.7 mm to calculate height and the horizontal format value of 4.9 mm to calculate width.

Varifocal cameras are very versatile and easy to work with.  There are different types of varifocal cameras just like there are different types of irises for cameras as described above.  Some varifocal cameras are manual varifocal cameras which means you must physically change the focal length on the camera.  Others are automatic and can be done through electronic controls associated with the DVR.

The key is to decide whether you will require a varifocal camera or not.   A camera placed at the end of a fairly straight, long driveway would be a good candidate for a varifocal camera as you can zoom in on objects (like cars and people) at the end of the driveway but as the object comes up the driveway you can still keep them in focus and good view.

On the other hand, a camera pointed at a doorway to simply monitor the movement through the doorway would not need to be a varifocal camera; a fixed lens camera would suffice.

As a side note:  Most all of the disguised or hidden cameras have 3.7 mm wide angle lenses and are fixed lenses.  The lens on these cameras is made such that

there is the maximum amount of distance that stays in focus without the use of a varifocal camera.

If you have any questions regarding varifocal lens or varifocal cameras, contact one of our security experts today via on-line “Live Chat” or by telephone at 866-573-8878 Monday through Friday from 9AM to 6 PM EST.


CCTV Digital Camera

Monday, January 31st, 2011

If the Digital Video Recorder or DVR is the heart of a digital video security system, then the CCTV digital camera must be the eyes. The cameras used today are top-notch technological wonders that provide high quality color video images. The have a vast selection of optional features that make their use extremely flexible and easy to use under almost any application.

A Closed Circuit Television or CCTV digital camera are the eyes of a digital security system because they are the devices that “see and capture” the action. There are many types of CCTV digital cameras available but they all “see and capture” using one of two similar methods. To describe how a CCTV digital camera works without getting too technical, we’ll tell you about their sensors and other parts of the cameras and how they integrate to get the job done.

Let’s divide the average CCTV digital camera into three parts: 1) The lens; 2) The sensor; and, 3) The analog-to-digital converter and all other supporting electronics.

The Lens
There are essentially two different type of lenses used in CCTV digital cameras. The first we’ll mention is the “fixed lens.” The fixed lens is so named because the focal length of the lens is stationary or fixed. This indicated that the lens as a definite range of focus as well as a fixed field of view. These lenses are excellent for cameras that are used in applications where the distance between the subject or object being recorded and the camera is usually constant. Examples of these uses include retail store shoplifting coverage, equipment monitoring, gate entrance monitoring, room surveillance, etc.

The varifocal lenses have a variable focal length. This means that these lenses can zoom in or zoom out on subjects or objects and be manually focused. This lens is a bit more expensive than a fixed lens. Applications for this lens would include uses where the camera position is changed on a regular basis or the field of view is changed often.

Either type of lens has basically the same function: Manipulate the light emitted by the image in the camera’s field of vision, so that it presents an incredibly high quality image that is focused on the cameras incredibly small sensor.

The Sensor
There are also two different type of lenses used in CCTV digital cameras. They take the focused light image and convert it into tiny electrical charges that can be used to create a digital video file or image. The two sensors used are the Charged Coupled Device or CCD and the Complimentary Metal Oxide Semiconductor or CMOS. At one time the CCD produced a high quality image than the CMOS at a slightly higher cost in price for the sensor. The CMOS on the other hand, used far less electricity to complete the task of creating the electronic video image. As time and technology progresses, the newer CCDs use less electricity and the newer CMOSs produce a higher quality image so that they are relatively similar in power usage, quality and cost.

Whether it’s a CCD or a CMOS, the sensor, with the help of supporting electronic circuitry, pass the image which at this point is in analog format, to the analog-to-digital converter.

The Analog-to-Digital Converter
CCTV digital cameras produce their finished product, the video image, in a binary or digital format. Since the equipment used along the way to produce the image does so basically using analog methods, the analog-to-digital converter is necessary to transform the analog signal into digital data. This converter is usually a relatively small Integrated Circuit (IC) chip that is designed specifically for this purpose. It must be very powerful and extremely fast in order to convert the signal for use in real-time (live).

When the signal leaves the analog-to-digital converter, it is now in digital form and ready to be sent to the DVR and/or monitor. This is done by one of two different methods as well. Either the signal is carried to the DVR using a video transmission cable (which in most cases is an RG-59 coaxial cable), or wirelessly converting the signal into a radio signal that can be transmitted for the camera to a corresponding receiver.

This should give you some working knowledge on how a CCTV digital camera works. If you need additional information or considering a purchase, please contact one of our security experts today using on-line “Live Chat” or by toll-free telephone at 866-573-8878.