The main task of the lens is to focus the light reflected from the object onto the matrix. If this part of the camera does not handle the duty well, all images will be of poor quality. But outdoor and home cameras need different fixed camera lenses. We will talk about how to select the element in this article.
Putting together a street box camera
The most significant difficulty in outdoor video monitoring is the variable illumination. Because of this, the camera assembling becomes more complex, and you will need to choose:
- lens mount;
- the size of the lens for the matrix and the corresponding resolution;
- a backlit device with day-night function;
- lens type and focal length for the system;
- aperture and its type.
Now let’s take a closer look at these points.
Choosing a lens for the size of the matrix
The quality of the image from surveillance cameras depends on the lens and matrix size ratio. For example:
- if the lens is smaller than the matrix, the picture will be darkened in the corners;
- if the lens is larger than the light-sensitive sensor, then part of the view will be lost as it remains out of frame. Plus, the effect of a telephoto lens appears, as when using a zoom.
A backlight in day/night conditions
If the camera is outdoor, you need to prepare the system for a variable level of illumination. To do this, buy cameras with an automatic day/night function.
In good light, that is, in the daytime, the filter cuts off IR light not to disturb the picture color rendering. At night, the IR illuminator helps to increase the camera’s light sensitivity and capture clear images.
You can learn more about this principle of shooting in the article: “Wireless night video surveillance cameras.“
The importance of focal length
Almost all components affect the overall quality of monitoring, but optical instruments play a more critical role. It is essential to determine the distance from the matrix to the lens; otherwise, without focusing, all video surveillance is meaningless because the images will be blurred.
Focusing is usually calculated in millimeters. For example, “2.8 mm camcorder lens”.
What cameras to choose and how to calculate the focal length you can find more in our article: “Competent choice of the camera focal length. 6 tips ”.
But there is another option for adjusting focus – a varifocal lens of video cameras with a variable focal length. This equipment can adjust the distance to the object, making it possible to see what is happening in more detail.
It is essential to consider not only the size but also the resolution of the matrix. It shows the number of pixels. And the more significant this parameter, the better the picture will be.
But the lens can limit the overall resolution of the camera. Therefore, you should choose an optical megapixel device with the same or higher resolution than the matrix.
To make it easier for you to find equipment, we have discussed TOP-5 cameras for outdoor surveillance for you.
Aperture and its diameter
The F-number (aperture) value is the result of dividing the focal length (in millimeters) by the corresponding aperture diameter. The lower this number, the more the lens collects light and transmits it to the matrix.
Typically, an optical instrument with a low F-number is more expensive.
The diaphragm can be automatic or adjustable. With the manual adjustment, the lens ring rotates to reveal the aperture opening. But this option is not convenient for outdoor video surveillance since the lighting is constantly changing.
In the automatic version, this all happens with the help of an electric drive based on the illumination level change.
The lens can affect the shooting quality, so there are many nuances to consider when choosing it. The main ones are the compatibility of optical equipment and the camera, matrix resolution, light sensitivity, sharpness, and viewing angle.
But before starting the purchase of devices and installation, you need to develop a surveillance plan. This will help to avoid many mistakes and overpayments.