How To Select the Lens for Your IP Camera System

What is the Best Lens for Your Surveillance Camera

The camera lens is a key component of your IP Camera System. It determines the desired field of view, clarity, and day/night performance of your surveillance camera. Many cameras come with a lens, so there’s a wide selection of cameras that include the correct lens for your application.

Before We Start, Consider Your Objectives

Your organization has determined that it needs surveillance cameras. This could be motivated by theft within the organization, concern about an intrusion that could lead to vandalism, or a safety concern. It’s essential to clarify the requirement. To learn more, read our article, Defining Your Objectives.

How Your Objectives Define the Lens

If your objective is to identify a person who is stealing equipment, you will need a camera and lens that provide sufficient resolution to identify the person. To determine how many people are gathering outside the building, you need a camera with a wide enough field of view to count them. If you plan to catch someone vandalizing a car in the parking lot, you need a camera and lens with good low-light capabilities. The objectives help you determine what to specify. Each location requires a camera that meets the objectives of that location.

Lens Specifications to Consider

The lens of an IP surveillance camera is defined by its angle or focal length, as well as its fixed, variable, or zoom capability, and F-stop.

If you are viewing a doorway and know the distance from the camera to the area you want to view, then a camera with a fixed lens is a good choice. If you are viewing a large room and are unsure of the best location for the camera, consider selecting one with a variable lens. Some cameras even have variable lenses that can be adjusted remotely from a computer (zoom lenses), allowing you to set up the ideal field of view quickly.

To learn more about camera placement, please read our article, What’s the Best Location for Surveillance Cameras.

Lens Angle or Focal Length of Lens

The lens angle and focal length are related specifications. They both indicate how wide or narrow the field of view will be at a certain distance. With a wider angle or a smaller focal length, you can see a wider area (field of view).

Though the focal length and lens angle are related, there is a difference between the focal length of a lens and the angle achieved by the camera. The focal length defines a lens, while the lens angle is determined by the size of the camera’s sensor, the distance from the lens to the sensor, and the lens’s focal length. The angle is the most essential specification when matching it to an application. Many of today’s cameras come with a lens. This makes it easy to select the right camera and lens for the job.

The lens angle is usually combined with sensor resolution. The combination of the lens angle and the sensor’s resolution determines the detail you can see at a specific distance.

Resolution of the Camera

The camera’s sensor determines the resolution or clarity you can see at a certain distance based on the angle of the lens. The resolution is defined as the number of pixels in the sensor. The more pixels, the better the resolution. High-resolution cameras can include sensors with upward of 12 megapixels.  We typically use the number of horizontal pixels across a target as the measure of clarity. For example, a 2-megapixel camera has typically an array of 1920 x 1080 pixels. We need approximately 80 horizontal pixels across a person’s face to identify someone you know. To recognize a person that you don’t know and compare them to a police photograph requires more resolution (about 160 pixels). To read a license plate number, we need about 50 pixels across a 12-inch license plate. To learn more, please read our article, What IP Camera Resolution Do You Need?

The Camera Resolution: Sensor Versus Lens Angle

The lens determines the distance required to achieve the necessary resolution across the target. The further away, the fewer pixels across the target. By adjusting the lens angle (or magnification), we can change the field of view and, consequently, the number of pixels across the target.

The wider our field of view, the fewer pixels per ft (or meter) we will get.  Let’s look at a simple example.  Take a look at the line below.  The line is broken into small sections or horizontal pixels.  The more elements (pixels/m or pixels/ft.), the more detail we can see.  As we view an object from a greater distance, the number of pixels per foot (m) decreases, and we can see less detail. The same thing happens when we widen our field of view. At a wider field of view, the pixel density decreases.

How the Lens Helps Cameras See in the Dark

The f-stop of the lens indicates the size of the aperture. The larger the aperture (i.e., the smaller the f-stop), the more light can reach the sensor. Light sensitivity is based on several factors. In film photography, light sensitivity was based on the ISO number. A film that had a higher ISO number was more sensitive to light. Today, the lens, sensor, and amplifier circuits in the camera collectively determine how well the surveillance camera performs in low-light conditions. Low-light cameras typically come with lenses that have an aperture of less than f/1.2.

The IP cameras available today switch to grayscale when there is low light. You can select cameras that can see objects by moonlight. To learn more about low-light level cameras, see our article, How to Set Up an IP Camera in Low Light Situations.

Summary of Lens Selection for IP Cameras

Selecting the correct lens depends on what you plan to view and the resolution you require. Identifying a person’s face requires a lens that allows you to have the proper number of pixels for identification. The field of view and the resolution of the camera are essential specifications.

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If you need assistance selecting the right lens for your IP camera system, please don’t hesitate to contact us.  We have extensive experience with IP camera systems.  You can reach us at 914-944-3425 or use our contact form.