The aperture of a camera is an important component that’s generally overlooked in most CCTV systems. Just having a basic understanding of how they work can help you to make more informed decision and get the most out of your device. The aperture size of a CCTV camera essentially sets a hard limit on how well it’ll perform in low-light conditions. Putting aside added features like supplementary IR light & software enhancements, the aperture ultimately has the largest impact on low-light performance.
What is an Aperture?
Put simply, the aperture is an opening that allows light to pass through the lens and into the camera’s sensor. Cameras and our own eyes work in virtually the same way, which can help make things easier to conceptualise. In the context of CCTV surveillance, there are only three main terms that we’re concerned with.
- Aperture: This essentially refers to the opening that lets light into the camera’s sensor. The aperture of a camera is equivalent to the pupil of our eyes.
- Aperture Stop: The aperture stop is the part of the lens that can open or close to let different amounts of light in (i.e. changing the size of the aperture). This is equivalent to the muscle in our eyes that dilates or contracts our pupils. Also referred to as a diaphragm.
- F-Stop: The F-Stop is a number that can tell us how wide the opening of the aperture is. The lower, the better it is for low-light surveillance.
What it means for your CCTV camera
The smaller the F-Stop of a camera, the wider the opening to the aperture is. As the opening to the aperture gets wider, considerably more light is able to pass through the camera’s lens and be picked up by its CMOS sensor. A smaller F-Stop is ideal for low-light and night-time surveillance, while a larger F-Stop is more suited for daytime or brightly-lit environments.
By changing the F-Stop of a CCTV camera from F2.0 to just F1.0, the amount of light received by the sensor is four times greater than before. This simple increase in light can have a few highly beneficial impacts on the overall image quality. Some of these benefits include reductions in motion blur, less grainy footage, and other overall improvements to low-light performance.
For most surveillance cameras, the aperture stop is a fixed size and can’t be adjusted to let more/less light in. This is done to reduce the overall complexity of the device and to keep costs down. As a result, these CCTV cameras tend to struggle more in low-light conditions than they would in well-lit areas. To compensate for this, cameras often have built in IR lights, use IR-cut filters, adjust the shutter speed, or use a range of software enhancements.
These extra features all have their own advantages and disadvantages, but there’s no complete replacement for a large aperture when it comes to low-light performance.
Effects on low light performance
For a camera to produce an image, it directs light into its CMOS sensor. The sensor converts the light into an electrical current, and then into a digital image that we can use.
To a camera, the light hitting the sensor is pure information. Too little information and the image will be underexposed, appearing darker and making it challenging to see details (above, left). Too much information and it’ll be overexposed, appearing washed out and creating extreme highlights (above, right).
Increasing or decreasing the F-Stop of a CCTV camera can have a few important impacts on the quality of surveillance footage. Most of these are visual artefacts we’ve seen before in CCTV footage or on our own smartphones & video cameras, such as:
- Motion Blur: CCTV cameras typically compensate for underexposed footage by decreasing the shutter speed. This does improve the lighting situation, but at the cost of footage quality. We see the effects of this drop in shutter speed in the form of motion blur. This is particularly noticeable in low-light environments.
- Grain & Noise: This artefact becomes an issue when cameras aren’t able to capture enough light to accurately record their surroundings. All cameras introduce some constant amount of noise to an image, regardless of lighting or exposure. In low-light settings, this noise gets amplified to a much greater extent than normal, resulting in grainy/noisy footage. This can be worsened by other software enhancements not equipped to handle underexposed images.
- Visible Range: As you’d expect, an insufficient aperture size will greatly reduce the visible range of a CCTV camera. With less light entering the sensor, the visibility drops off exponentially with distance.
- Lens Flare: Surveillance cameras with large apertures tend to be more susceptible to visual artefacts like lens flares. This is no longer such an issue with enhancements like Highlight Compensation (HLC), Backlight Compensation (BLC), and WDR technology.