Sony FCB camera blockWith the rapid adoption of underwater ROVs/AUVs in water conservancy tunnel inspection, marine engineering O&M, underwater security screening, and subsea pipeline monitoring, visible-light cameras have become the core "eyes" through which underwater robots perceive their environment.
When selecting cameras, many R&D teams first turn to fixed-focus cameras that are simpler in structure and lower in cost: cost-effective fixed-focus solutions such as starlight full-color USB camera modules and black-light full-color network camera modules. These offer excellent color night-vision imaging and a compact size, making them easy to integrate into FPV systems, small robots, and even underwater enclosures. In fixed scenarios, they are indeed very reliable choices. However, after a project has run several underwater missions, teams often find that the limitations of fixed-focus solutions begin to emerge—the real operating scenarios of underwater robots are not the ideal environment assumed by fixed focus, namely "cruising at a fixed altitude and observing targets of a fixed scale."
Ⅰ. What Is Fundamentally Different Between Fixed Focus and Zoom?
Many people assume the difference is merely "whether the image can be magnified." In fact, the underlying imaging logic is completely different:
1. A fixed-focus camera's lens focal length is completely fixed, leaving no room for field-of-view adjustment. It can only output clear images within a specific distance range preset at the factory. If the target is too far away, defect details are compressed into a tiny point in the image and cannot be resolved at all. If the target is too close, it directly exceeds the focusing range and the entire image becomes blurred.
2. A zoom camera supports optical continuous zoom, allowing seamless switching between wide-angle panoramic views and telephoto close-ups without moving the robot body at all. It can first complete a full-area environmental scan at a distance, and after identifying a suspicious point, directly apply optical magnification to clearly capture millimeter-level details such as cracks, corrosion, and tiny weld defects.
Ⅱ. Why Fixed-Focus Cameras Cannot Avoid Shortcomings in Underwater Environments
In real underwater scenarios, visibility, obstacle distribution, and operational boundaries are completely uncontrollable. The inherent deficiencies of fixed-focus solutions are amplified indefinitely, directly affecting operational safety and inspection efficiency:
1. Safety Constraints Prevent Close-Proximity Observation
In many underwater operations, the facilities being inspected are surrounded by sharp protruding structures, underwater currents and vortices, and entangling aquatic plants. The robot simply cannot approach the target surface without limit. If a wide-angle fixed-focus camera is selected, only the overall outline of the facility can be seen in the image. Key defects such as millimeter-level cracks, corrosion holes, and weld porosity are directly compressed in the image and cannot be identified by the naked eye. If a narrow-angle fixed-focus camera is selected, the effective field of view is extremely small. A slight deviation in the robot's heading will cause it to miss surrounding hazards, and it is also very easy to collide with obstacles and damage the equipment.
2. Multi-Scale Requirements Within a Single Mission Cannot Be Covered by a Single Fixed-Focus Camera
Most routine underwater inspection missions require both large-area full coverage and local defect re-examination. A fixed-focus camera can only choose one of the two: either sacrifice detail for a large field of view, or sacrifice field of view for detail clarity. To meet both requirements simultaneously, three or four fixed-focus cameras with different focal lengths must be packed into the robot's cramped enclosure, directly increasing hardware cost, overall power consumption, and wiring complexity, while also consuming valuable underwater enclosure space.
3. Dynamic Fluctuations in Water Visibility Invalidate the Fixed-Focus Clear Range
The content of suspended matter and sediment in water changes at any time, so the actual effective observation distance is not a fixed value. A fixed-focus camera's clear imaging range is a factory-preset fixed value. Once water turbidity changes and the effective observation distance shifts outside the preset range, image clarity drops sharply, making stable imaging performance impossible to guarantee.
Ⅲ. Zoom Cameras Give Underwater Robots More Freedom
Adding an optical zoom camera has never been about pursuing the gimmick of "higher-grade specifications." It is about fundamentally solving the multi-scale observation pain points of complex underwater scenarios:
1. Integrated Near-and-Far Observation Without Repeatedly Moving the Robot to Adjust Distance
Through continuous optical zoom adjustment, wide-angle mode can quickly complete a large-area full scan and efficiently locate suspicious targets. After switching to telephoto mode, tiny defects such as pipe-wall corrosion, concrete cracks, marine growth, and damaged anchor-chain wires can be clearly seen from a safe distance. The robot does not need to repeatedly advance and retreat to adjust its position, greatly reducing collision and entanglement risks and improving inspection efficiency several times over.
2. One Camera Covers the Full Scenario, Greatly Simplifying Overall Integration
A single optical zoom camera can simultaneously cover two core operating modes: wide-angle full-area inspection and telephoto detail re-examination. There is no need to pack multiple fixed-focus cameras into a cramped underwater enclosure, directly saving enclosure space, reducing unnecessary wiring, waterproof sealing, and power supply module development work, and lowering the overall design complexity of the system.
3. Dynamic Adaptation to Different Visibility Levels, Greatly Improving Environmental Adaptability
A zoom camera can flexibly adjust focal length according to real-time water turbidity, while combining the camera's built-in exposure, wide dynamic range, and noise reduction algorithms to optimize imaging. In clear water, telephoto can be used to magnify and capture subtle defects; in turbid water, wide-angle can be used to maintain overall environmental awareness. This allows the same robot to operate stably in waters of different quality and depths without changing to equipment with different lenses for different scenarios.
4. High-Definition Close-Up Documentation to Support Full Engineering Lifecycle Assessment
High-definition defect close-up images captured by a zoom camera can be fully retained as original image data, directly used for engineering inspection reports, facility health risk assessment, and full-lifecycle project archiving, providing intuitive and traceable visual data support for long-term health monitoring of underwater facilities.
Summary
Fixed-focus cameras are not unusable. In scenarios with a fixed working distance, a single observation target, and completely stable imaging requirements, they can even be a more cost-effective choice than zoom.
The core value of a zoom camera is that it gives an underwater robot the ability to freely switch field-of-view allocation. When the same device needs to complete three different levels of observation—full-area search, target identification, and detail re-examination—at distances ranging from several meters to tens of centimeters, zoom allows it to complete the entire workflow from a safe distance without repeatedly moving the robot body to change imaging conditions.
Therefore, judging whether an underwater robot should be equipped with a zoom camera must not remain stuck in the selection misconception that "zoom is more advanced." It should return to three core variables: the project's actual operating distance, the scale of the target being inspected, and the required observation level. Only by choosing according to actual needs can the most cost-effective implementation solution be selected.
FAQ
Q: Are underwater zoom cameras structurally more complex and therefore more prone to waterproof failures than fixed-focus cameras?
A: Not at all. The risk of waterproof failure in an underwater robot depends primarily on the sealing process of the overall enclosure and has no direct correlation with whether the camera itself uses a zoom or fixed-focus structure. As long as standardized enclosure waterproofing design is implemented, the long-term underwater reliability of zoom cameras and fixed-focus cameras is completely equivalent.
Q: How do you distinguish optical zoom from digital zoom? Which should be preferred for underwater engineering inspection projects?
A: Optical zoom relies on the physical movement of lens groups inside the lens to magnify the image, without losing native image quality throughout the process. Digital zoom simply crops and magnifies the original image output by the sensor, and image clarity drops noticeably after magnification. Underwater engineering inspection projects must choose optical zoom solutions.
Author
Danny Wong, Co-founder & Chief Technology Officer of Xuanzhan Technology, compiled in September 2026.
Shenzhen Xuanzhan Technology Co., Ltd., an officially authorized distributor of Sony (China), has 17 years of experience in HD video secondary development and implementation. It has independently developed IP / SDI / HDMI / USB / MIPI multi-type interface encoding control boards, and also provides a DSLR camera network control board compatible with the ILX-LR1. It can provide pre-sales solution consulting, on-site debugging, and after-sales technical support, support connection with Sony's original factory technical resources, and solve project problems on site.