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WECU Surveillance Security Cameras!

We have all the security camera Lenses & Information you will ever need!!

Quick Reference

There are many factors involved in choosing a suitable lens, as the lens size increases the left to right field-of-view narrows and the distance increases.


• A variable focus 1.8mm ~ 3.6mm lens is ideal for monitoring hallways, doorways, and average size rooms
• A 5.0mm ~ 40mm lens has the ability to be used for monitoring hallways and doorways and can be easily adjusted to monitor long driveways or areas several hundred feet away.


Beware of many online lens calculators which produce inaccurate angle measures for these focal lengths. Also, most 1/4" CCD cameras produce a significantly narrower field of view with the same focal length lens.

Due to the physical nature of lens optics, the numbers listed below should be considered accurate to within ± 3° and therefore a few feet / meters as well. They are intended as approximate guidelines to help select the appropriate lens, while each camera in fact has its own unique field of view with each specific lens. In addition, C- and CS-mount lenses typically deliver a slightly narrower field of view than our comparable board lenses.

Lenses wider than roughly 5mm produce "artificially" wider fields of view than more telephoto lenses. In order to do so, the video image is slightly curved at the edges of the screen. While this artificial distortion is nominal for focal lengths between 4.3 and 3.6mm, curvature increases with wider angle lenses.

Each size lens is available with a manual or auto-iris lens.


• The manual-iris lens is more affordable but should only be used in indoor applications where the light source remains constant
• The auto-iris lens can be used for indoor areas with varying light conditions as well as outdoor installations.


HELP ON HOW TO SELECT LENSES:


• SELECT SIZE: if your camera has 1/3" imager size you can go for 1/3" or 1/2" lenses. If your camera has 1/2" imager size you can use 1/2" lenses.
• SELECT MOUNT TYPE: in 90% of cases it will be CS, check your camera's manual
• SELECT FOCAL LENGTH: If camera is strictly indoors and light never changes go for manual iris lenses
• SELECT TYPE OF IRIS: if camera is for outdoors or light changes go for DC iris lenses (camera must support DC iris lenses) or video auto iris lenses
• Varifocal lens will give you flexibility in adjustable field of view.


SOME COMMON QUESTIONS:


• What is LUX?


During the day the amount of illumination reaching a scene depends on the time of day and atmospheric conditions. Direct sunlight produces the highest-contrast scene, allowing maximum identification of objects. On a cloudy or overcast day, less light is received by the objects in the scene, resulting in less contrast.

To produce an optimum camera picture under the wide variation in light level (such as occurs when the sun is obscured by clouds), an automatic-iris camera system is required. Typically, scene illumination measured in foot-candles (ftcd) can vary over a range of 10,000 to 1 (or more), which exceeds the operating range of most cameras for producing good quality video images.

The chart below summarizes the light levels occurring under daylight and these low light level conditions. The equivalent metric measure of light level (lux) compared with the English (ftcd) is given.

• What does Manual Iris Lens mean?


Manual iris lenses provide an effective solution for applications where the scene and lighting requirements are relatively stable, especially when used with security cameras that are equipped with electronic shutters.


• What does Auto-Iris Lens mean?


Auto iris lenses produce consistent video signals in scenes with varying light levels, thus enabling reliable surveillance in areas that would otherwise be compromised.


• Should I use Manual or Auto Iris Lenses?


You can save money and use Manual Iris Lens only when scene illumination never changes.
Example: illuminated store or office. If the light changes a lot it is recommended using Auto-Iris.


• What's a Varifocal Lens?


The Varifocal lenses are ideal in situations where the security camera surveys a distant point. One can adjust the zoom and focus of these lenses either manually or automatic. Often it si not possible to determine the focal length of a lens required to meet a particular application or install, it is possible the angle or FOV - Field of view cannot be achieved by a standard lens. So a manually or remotely zoomed lenses have been developed to meet these not so specific applications. These are known as " Vari-Focal " lenses or Variable focal length lenses and are available in a many different focal length configurations, but mot too many to make it confusing. The exact angle of view can be set at the installation point but it is important to ensure that the FOV - Filed of View required has been addressed prior to installation and is available within the lens's range, for example 3-12mm or 9-22mm etc...


• What Focal Length will I need?



• The smaller the focal length number = the wider the field of view.
• If you have a security camera in the office or warehouse and you want to see as much as you can, you should go for 2.8 or 4 mm lens this makes a wide, somewhat distant view
• If you want to observe a limited area, like an entrance you should go for 8mm or 12mm this makes a narrow view and objects are closer.
• Send us a E-mail and we can help you determine what security camera lens will best suit your location.
• Use Varifocal lenses for flexibility in choosing the best field of view.



• What is the field of view (FOV) How much will the security camera see?


The field of view (FOV) is based on the camera & lens. WECU Surveillance.com has many different types of Lenses to suite any and all of your CCTV security camera needs. Wide angle lenses are suitable for most applications due to their ability to view a large area. A 4mm wide angle lens will be able to view an area 20' high x 26' wide at 21' away.

As an example, a 15' x 15' room is shown in the diagram below. Observe that the 4mm lens (green arrows) allows better wide angle viewing coverage than the 12mm lens (red arrows). In applications where a closer view is needed (such as above a cash register or over a greater distance), an 8 or 12mm may be desired. The same camera (above) at 21’ away with a 8mm lens will have a 10' vertical x 13' horizontal FOV.

At 21' with a 12mm lens, the FOV will be approx 6' vertical x 9' horizontal. Increasing the focal length of the lens decreases the perceived distance to the viewing area. See the FOV diagram below for approximate views with different focal length lenses.

DEPTH OF FIELD The depth of field refers to the area within the field of view which is in focus. A large depth of field means that a large percentage of the field of view is in focus, from objects close to the lens often to infinity. A shallow depth of field has only a small section of the field of view in focus. The depth of field is influenced by several factors. A wide angle lens generally has a larger depth of field than a telephoto lens, and a higher F stop setting typically has a larger depth of field than a lower setting. With auto iris lenses, the automatic adjustment of the aperture also means constant variation of depth of field. The small depth of field is most apparent at night when the lens is fully open and the depth of field is at its minimum. Objects that were in focus during the day may become out of focus at night Choosing the right Lens

Once you have selected a camera, the next step is to select the appropriate lenses and any other relevant components necessary in the system.
There are two main lens mount standards called C-mount and CS-mount. They both have a one-inch thread and they look the same. What differs is the distance from the lenses to the sensor when fitted on the camera:

• CS-mount. The distance between the sensor and the lens should be 12.5 mm
• C-mount. The distance between the sensor and the lens should be 17.5 mm. A 5 mm spacer (C/CS adapter ring) can be used to convert a C-mount lens to a CS-mount lens

The initial standard was C-mount, while CS-mount is an update to this, allowing for reduced manufacturing cost and sensor size. Today, almost all cameras and lenses sold are equipped with a CS-mount. It is possible to mount an old C-mount lens to a camera with CS-mount by using a C/CS adapter ring. If it is impossible to focus a camera, you probably have the wrong type of lens.

Sensor size

Image sensors are available in different sizes, such as 2/3", 1/2", 1/3" and 1/4", and lenses are manufactured to match these sizes. It is important to select a lens suitable for the camera. A lens made for a 1/2" sensor will work with 1/2", 1/3" and 1/4" sensors, but not with a 2/3" sensor.

If a lens is made for a smaller sensor than the one actually fitted inside the camera, the image will get black corners. If a lens is made for a larger sensor than the one actually fitted inside the camera, the angle of view will be smaller than the default angle of that lens – part of the information being "lost" outside of the chip (see illustration below).

Image sensors: CCD vs. CMOS

The image sensor of the camera is responsible for transforming light into electrical signals. When building a camera, there are two possible technologies for the camera's image sensor:

• CCD (Charged Coupled Device)
• CMOS (Complementary Metal Oxide Semiconductor)

1/3-inch CCD sensor

1/4-inch CMOS sensor

CCD and CMOS are the critical components that act as a camera's "digital film." CCD sensors are produced using a technology developed specifically for the camera industry, while CMOS sensors are based on standard technology already extensively used in memory chips like inside PCs, for example. Today's high quality cameras use mostly CCD sensors. Although recent advances in CMOS sensors are closing the gap, they are still not suitable for cameras where the highest possible image quality is required. However, CMOS sensors may be ideal for entry-level cameras where size and price are important factors.

CCD technology

CCD sensors have been used in cameras for more than 20 years and present many advantageous qualities; among them, better light sensitivity than CMOS sensors. This higher light sensitivity translates into better images in low light conditions. CCD sensors are, however, more expensive as they are made in a non-standard process and more complex to incorporate into a camera. In addition, when there is a very bright object in the scene (such as a lamp or direct sunlight), the CCD may bleed, causing vertical stripes below and above the object. This phenomenon is called a smear.

CMOS technology

Recent advances in CMOS sensors bring them closer to their CCD counterparts in terms of image quality, but CMOS sensors remain unsuitable for cameras where the highest possible image quality is required. CMOS sensors provide a lower total cost for the cameras since they contain all the logics needed to build cameras around them. They make it possible to produce smaller-sized cameras. Large-sized sensors are available, providing megapixel resolution to a variety of network cameras. A current limitation with CMOS sensors is their lower light sensitivity. While this drawback is not an issue in bright environments, in low light conditions it becomes apparent. The result is either a very dark or a very noisy image.

Lens distance examples:

Distance from Camera to vehicle is 40 feet


3.8mm - Picture area 49' w x 37' h

6mm - Picture area 31' w x 23' h

8mm – Picture area 24' w X 18' h

15mm – Picture area 13' w X 10' h

55mm – Picture area 4' w x 3' h



General Security Camera Lens Information:

The lens of a security camera is like the cornea of your eye. Without it you can not see, and neither can the security camera. There are many different types of security camera lenses in the security camera market.
The first division between lenses are the wide angle and the zoom lens.
The next division is between the auto iris, manual iris, or no iris at all.
These choices and others depend on the intended use of your security camera system. Correct security camera lens choice should be determined by your application and your requirements.