Published on November 9, 2018 by Matt Garnham in Blog Posts on Security Cameras
Security Camera Focal Lengths
This is the most important thing to consider when selecting the right security camera. If this is wrong, it doesn’t matter what else you do, you won’t ever achieve optimal surveillance images.
What is the Focal Length?
To explain this better, you need to know about a couple of the important internal components of a security camera. Don’t sweat it – I’ll keep this as simple as I can!
Image Sensor of a Security Camera
The image sensor of a security camera is the electronic component that converts light into an electrical signal. You may see these referred to as CCDs (charge couple device) or CMOS (complementary metal-oxide semiconductor).
It’s beyond the scope of this blog post to explain the pros and cons of each of these different CCTV camera components.
Security Camera Lens
The lens of a surveillance camera is the camera’s window to the world. This is a piece of glass (or in some cases, a piece of plastic). The lens focuses the light from the outside world onto the image sensor of the CCTV camera.
There are 2 general types of lenses for security cameras. Fixed and Varifocal Lenses. I will expand on this a little later.
The Focal Length of a Surveillance Camera
Ok – back to the focal length of a surveillance camera. The focal length is the gap between the image sensor and the lens. A CCTV Camera’s focal length is measured in millimeters (mm). This is the distance between the lens and the image that is required for a particular lens to produce a sharp image.
You will see an image that is out of focus if the distance between the image sensor and the lens is not exactly right.
Different Lenses Fitted To Security Cameras
There are an almost infinite number of different possible lens combinations, however they are broken down into 2 sub categories.
- Fixed Security Camera Lenses
- Varifocal Security Camera Lenses
Fixed Security Camera Lenses
These are lenses that have 1 fixed focal length setting. They have no adjustment. You get what you are given. You can not adjust them. If the focal length is not suitable, then tough.
There are many different fixed lens options, however the most common one is a 3.6mm Lens. This results in an angle of view a little over 90°. This will allow you to identify people at around 20 feet. This is a great lens for giving a general overview of an area, but unless people get close to the camera, you won’t identify them.
We also stock a smaller range of other fixed lens CCTV cameras. The 8mm Lens. This results in an angle of view a touch greater than 40°. A camera with this lens will identify people at around 40 feet. This is a good budget lens for a more focused, targeted camera view to identify people, without the added expense of a varifocal lens.
Varifocal Security Camera Lenses
These are lenses that are adjustable (zoom and focus) between two different focal length settings. You can adjust the distance at which the camera can identify a person.
Again, there are a lot of different varifocal lens options out there. The most common lens is a 2.8-12mm Lens. This is a lens that can be adjusted between the ultra wide 2.8mm and the telephoto 12mm. At 2.8mm you will see an angle of view a little over 100°, but the identification distance will only be around 10 feet. At 12mm you will achieve around a 30° angle of view and identification at around 50 feet. The real trick is that this lens can be set to anywhere between those two different focal lengths. This means you don’t waste any part of the image.
We stock 2 other varifocal lenses that are really helpful. The first of these is the 6-22mm Lens. At 6mm the angle of view is a little over 40° and around 35 feet for identifying a person. At 22mm the angle will be around 16°, identification at about 80 feet. This is a great mid-range telephoto lens.
Now the big dog! The 5-50mm Lens is not one you will see at many of our competitors. A camera with this lens really can be the silver bullet allowing identification at up to 230 feet! At 5mm the angle of view is a little over 50° with an identification distance of approximately 30 feet. But you wouldn’t use this camera for that! At 50mm however the angle of view is just 7°, but the identification distance is a whopping 230 feet. Often our customers will tell us they have caught identifying images of perpetrators before they even know there are security cameras.
How Different Focal Lengths Compare
Here’s a quick reference table showing how the different focal lengths compare. The numbers are approximate and the identification distances can vary depending on lighting and other environmental conditions so these are sometimes considered pessimistic.
|Lens Focal Length||Angle of View||Identification Distance|
If you get the focal length of a security camera right, it’s incredible the detail you can see and how effective your security camera system will be. On the other hand, getting the lens focal length wrong will result in an image where you can see what is going on, but not enough detail to identify a person by.
Our customers often have trouble deciding on what lens is best for whatever situation they have. Fortunately, we have a team with a huge amount of experience and are willing to help you out. Feel free to get in touch and we will help!
about the author: Matt Garnham
Security Camera expert for many years. He is the founder and owner of Orange Security. Started life in the security industry in the UK. Relocated to Southern Florida and Orange Security was formed.