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Tech Focus: Understanding Autofocus-Zoom Technology

June 26, 2024

Autofocus-zoom (AF-Zoom) cameras are sophisticated devices designed to deliver high-quality image data. In this Tech Focus we take a look at the technology behind autofocus-zoom systems and some of the factors which influence their effective operation.

What is an AF-Zoom block camera?

An autofocus-zoom block camera is a compact, integrated camera module that combines advanced zoom capabilities with automatic exposure and focus functions. These cameras are designed to offer high-resolution imaging and precise focus control over a wide range of distances. They are commonly used in applications that require dynamic focus adjustments and detailed zoom functionality, such as UAVs and ROVs, medical imaging, industrial automation, surveillance and traffic monitoring.

The technology behind AF-Zoom cameras

Zoom lenses

An AF-Zoom camera will often quote both optical and digital zoom. You can read in detail what these mean and how they differ in our previous Tech Focus, Digital Zoom vs. Optical Zoom.

Basically, optical zoom lenses magnify distant objects while maintaining image quality. This is achieved by physically adjusting the lens elements inside the camera to alter the focal length. Digital zoom enhances the image electronically and, while this can extend the zoom range, it usually results in a loss of resolution.

Autofocus systems

There are several technologies which can achieve rapid and accurate focus in a variety of conditions and applications. Each autofocus system has its advantages and disadvantages, making them suitable for different scenarios. Autofocus systems can be categorized as either active or passive based on how they operate.

An active system relies on emitting a signal such as infrared light, laser or ultrasonic waves. Laser focus, for example, is used in many mobile phones.

Passive systems include: Contrast Detection Autofocus (CDAF); Phase Detection Autofocus (PDAF); Hybrid Autofocus; and Dual Pixel Autofocus (DPAF)

As an example, CDAF provides accurate focus by analyzing the image contrast directly from the camera’s sensor. The camera adjusts the focus by moving the lens elements until the highest contrast is detected within the image. High contrast usually indicates that the image is in focus. This system is very effective in static scenes where precise focus is critical but can be slower compared to other methods, especially in low-light or low-contrast environments.

Zoom and iris aperture also affect CDAF, with each factor influencing the depth of field and the camera’s focusing performance. When zooming in (increasing the focal length) the depth of field becomes shallower, meaning the range within which objects appear sharp decreases. This makes focusing more critical because even minor focus errors become noticeable. In contrast, at shorter focal lengths (zoomed out), or when using a wide-angle lens, the depth of field is deeper, so more of the scene will appear in focus, making focusing generally easier and more forgiving.

The size of the iris aperture, indicated by the f-number, also plays a significant role. A larger aperture (small f-number, such as f/2.8) allows more light to hit the sensor but results in a shallower depth of field. This narrow focus area demands precise focusing, as it can be challenging to maintain sharpness across the desired subjects. On the other hand, a smaller aperture (large f-number, such as f/16) provides a deeper depth of field, allowing a larger portion of the scene to be in focus. However, this also reduces the amount of light reaching the sensor, which can affect CDAF.

Lighting conditions further influence how well CDAF performs. In bright conditions, the autofocus system works better because the sensor can easily detect more details and contrast differences . However, in low-light situations, the overall contrast in the scene is reduced, causing the autofocus system difficulty in finding an accurate focus. This can lead to slower focus acquisition and more frequent “hunting” for the correct focus point.

When combining zoom with a large aperture, the resulting very shallow depth of field requires extremely precise focusing, and the CDAF system may struggle more due to the narrow focus area and potential lack of contrast. Conversely, using a wide-angle lens with a small aperture results in a deep depth of field, making focus less critical and allowing the autofocus system to perform more reliably, even with some variation in contrast levels. Thus, the interplay of zoom, aperture, and lighting conditions are influencing factors on the performance and accuracy of CDAF.

Harrier autofocus-zoom technology

Most AF-Zoom cameras go out of focus when zoomed in, so after a zoom-in, users have to manually focus, or set the autofocus feature on. Many cameras have AF modes that trigger a single autofocus operation on demand, after a zoom, or at regular time intervals.

Our range of AF-Zoom block cameras offers a variety of advanced optics and precise autofocus technology, providing versatile solutions across various industries. For example, our Harrier 36x AF-Zoom Camera has been designed to electronically track the focus as the camera zooms so that the user doesn’t have to manually adjust the focus or trigger the AF as often.

Harrier block cameras feature multiple output options, including LVDS, 3G-SDI, USB3, HDMI and IP, compact size and light weight, global shutter models, HD or 4K resolution and from 10x up to 55x zoom.

Applications for Harrier AF-zoom cameras include unmanned aerial and underwater vehicles (UAVs, drones and ROVs), traffic and rail monitoring, pipe inspection and remote monitoring, medical applications and many others. Their ability to deliver high-quality images and video with dynamic focus adjustments makes them indispensable tools in modern imaging applications.

Browse more information on our latest AF-Zoom cameras and their specifications, or contact our sales team to find the right model for your requirements.