Below is a guide we have created for the sole purpose of educating you on the various terms that go along with the CCTV or security camera lenses. There are a lot of them, much more than they are even described below, but it is important because the lens is a crucial part of your video surveillance. Knowing which lens to choose can save you time, money and will increase the likelihood of capturing exactly what you intend.
And as always, if you need a security camera lens and do not feel like reading below, just give us a call and we’ll be glad to help – 1-877-926-2288
If you already know the specs of a particular lens, test it on our lens calculator to find out the field of view the lens is capable of capturing.
Focal length (mm)
The focal length (measured in “mm”) of a lens determines how far the camera can see. The most common focal length in security cameras is 3.6 millimeters, which will allow for approximately a 72-degree field of view (FOV described below). This focal length works well for residential or small office surveillance applications.
If you can only learn one thing about safety camera lenses, you should know that the greater the focal length, the further away it can focus. The smaller the focal length, the greater the field of view.
Field of view (FOV)
Field of View is the area, in width, that the lens will allow you to see. If you hear the term “wide angle” then it will have a smaller lens, such as 2.8mm. That means that only what it looks like, the image will be broader. With smaller focal length details are also more difficult to see. If you are capturing video in a normal sized room, maybe 20x20ft then a wide angle lens will work just fine. If you need to capture a person’s face, then you will want to consider something with a longer focal length, such as 16mm.
Monofocal Vs. Varifocal
Monofocal lenses or “fixed” lenses can only focus at a specific distance … “mono” -> one -> one length! They will have a focal length, such as 16mm or 3.6mm. They are generally cheaper than variable focal length lenses, which will allow you to adjust the focal length manually. Variable focal length lenses usually have a range, such as 2.5-6mm or 5-50mm. The zoom lenses are similar to the varifocal, except the focal length will adjust electronically, thus they are generally more expensive.
CCTV zoom lenses are little more expensive because, well, they are better. They can automatically adjust focus to increase the setting on a particular object.
Vs. manual Auto Iris
This is very similar to the choice between Monofocal and Varifocal, where one is fixed and the other “varies”, and therefore is more expensive. The iris has to do with how much light is allowed to filter through the lens. The “fixed” or iris lens manual is one that you would use if you are in an area where lighting does not change, such as an office. An auto iris lens will automatically adjust the light variations. You’ll probably need an auto-iris lens for outdoor surveillance.
Also important for various lighting conditions is the camera’s LUX rating.
Camera / Picture Format
Here, we are referring to the camera’s CCD image sensor. You will notice that most of the CCTV cameras list 2/3, “a half,” 1/3 “or 1/4” for your CCD image sensor. This will affect your field of vision. The larger the image sensor, the larger the field of view the camera has. For example, two-thirds “will see more than a 1/3” image sensor. Now, all of the above applies only to the camera, not the lens. By the lens, what is important to note is that regardless of the shape of the lens image, say “1/3 inch image format” is the maximum size it will allow. So, for example, to a camera with a half “CCD imaging device you would want a 1/2” or larger lens, or there will be a ring on the outside of the lock on the outside of the image.
Aperture Rate (F-Stop)
Aperture, measured in F numbers, is the camera’s ability to capture light. The smaller this F number is, the larger the aperture the lens will be, the more open its lens, and the better it will be to allow light passing and the CCD image sensor. For example, if you see the lens has a low aperture of F1.2, then it will work well in low light situations. Consider your eye, as your student will dilate or contract depending on how much light there is. If you are in a particularly dark area, your pupil dilates to allow more light so you can see better.
C or CS Mount
When mounting a lens from a CCTV security camera from Entertainmentdns.com, you will get C or CS to choose from. Both the lens and the camera will specify what they are. Many cameras say “C / CS mount”, which means it will allow you to mount either.
The difference between the two is the distance between the image sensor and the lens ….
C Mount – 17.5mm CS Mount – 12.5mm
Tip:Not having the correct lens is a common cause for not having clear images.
Hard drive or direct drive
The video and direct drive refers to auto iris lenses. Repeat from above, automatic iris lenses allow variations in lighting conditions. Video lenses contain amplifier drive circuits that will allow diaphragm control to operate. Direct drive lenses will require the camera to contain the amplifier circuit. Be sure to check the product options as some Direct Drive lenses may include an adapter that will convert it to an Auto iris lens Video Drive.
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