Underwater imaging systems operate in unforgiving conditions. With distorted light, colour absorption and particle scattering all significantly reducing visual definition, optical components designed for standard cameras simply won’t perform in such harsh environments. From dome ports to bandpass filters, every optic in an underwater camera housing plays an important role in delivering optimal image performance.
For remotely operated vehicles (ROVs), autonomous underwater vehicles (AUVs) and towed camera rigs, accuracy is non-negotiable. For example, undetected defects in oil and gas assessments can cause catastrophic environmental damage; poor visibility in military and defence operations can jeopardise crucial reconnaissance, and unreliable imaging in marine wildlife research may lead to flawed data and, therefore, missed discoveries. The optics integrated into this equipment are integral to reliable and precise imaging – and getting each element right is vital.
Dome Ports vs Flat Port Windows
Among the primary optics in these camera housings are underwater optical ports. Sometimes referred to as lens ports, they protect key internal components without compromising image quality. For subsea operations, they’re generally split into two categories: dome ports and flat ports – and the one you use is determined by your field of view (FOV) requirements.
Dome Port Optical Windows
Dome ports deliver a wider FOV (typically above 63º) while avoiding image distortion in comparison to flat ports. This makes them ideal for use with setups that incorporate wide-angle lenses in subsea imaging scenarios such as large-scale pipeline or infrastructure assessment, seabed surveying and sea life monitoring, as well as broad-area surveillance.
Flat Port Optical Windows
In cases where a wide FOV isn’t required – usually under 63º – flat ports (sometimes known as macro ports) are often the more effective option. They also magnify more than domes. As light refracts through a flat window from water, it creates a virtual image that appears closer and larger than the subject. This makes flat ports typically better suited to macro lens configurations and narrow-view applications such as close-ranged weld inspections and detailed hull corrosion monitoring.
To enhance durability in underwater housings, both dome and flat-port optical windows are commonly manufactured from sapphire, N-BK7 and acrylic (PMMA). Recommended optical coatings include anti-reflective (AR) coatings to minimise reflection and optimise transmission, and hydrophobic coatings to repel water droplets from the surface.
Underwater Camera Lenses
Alongside plastic and glass ports, underwater housings also feature lenses to focus and direct light to the camera’s sensor. With the water-air interface at the port already introducing optical distortion, the lenses behind underwater cameras need to be engineered to compensate for it. As a result, aspheric lenses are commonly specified for their ability to reduce, and in some cases eliminate, aberrations.
At Knight Optical, we supply individual precision aspheric lenses for integration into bespoke underwater imaging systems.
Underwater Bandpass Optical Filters
One of the most common challenges in all forms of subsea imaging is colour distortion. Water absorbs red light first, which often leaves underwater videos and images looking washed out. By using optical filters centred on red wavelengths, more red light reaches the detector, ensuring images look natural and, importantly, offer full clarity.
Blue bandpass optical filters, on the other hand, are beneficial when artificial light is part of your setup. By controlling the light’s intensity, they reduce any harshness that may compromise the captured image.
Whether it’s a BK7 glass underwater window for handheld underwater photography or a precision aspheric lens for an ROV inspection system, Knight Optical supplies stock and custom-made optical components to meet your exact specifications. To find out more, contact a member of our team today.