Abstract
In fields such as biology, archeology, and industry, underwater photogrammetry can be achieved using consumer-grade equipment. However, camera operations underwater differ considerably from those on land because underwater photogrammetry involves different optical phenomena. On the basis of the requirements and specifications of the marine vessel Polaris, we developed a novel underwater camera with prime and zoom lenses and a high resolving power. The camera can be used in the spectrum in shallow water and the blue–green spectrum in deep water. In the past, ordinary cameras would be placed in waterproof airtight boxes for underwater photography. These cameras were not optimized to the underwater spectrum and environment, resulting in no breakthroughs in resolving power. Furthermore, the use of the blue spectrum greatly increases during underwater and particularly deep-water surveying. Chromatic aberration and focus-point displacement generated by the shift from the shallow-water spectrum to the blue–green spectrum in deep water makes universal underwater photography even more difficult. Our proposed optical design aimed to overcome such challenges for the development of a high-resolution underwater surveying camera. We designed a prime lens and a zoom lens. We adopted a waterproof dome window on the outer surface as the basic structure and optimized it in accordance with the conditions of different water depths and spectra to obtain distortion within ±2% and high-resolution underwater imaging quality. For the zoom lens design, we employed a genetic algorithm in Zemax to attenuate chromatic aberration as a kind of extended optimization. This novel optical design that can be used in all waters is expected to greatly reduce the volume and weight of conventional underwater cameras by more than 50% and 60%, respectively, and increase their resolving power by 30–40%.
Highlights
Underwater photogrammetry, similar to terrestrial and aerial photogrammetry, has advanced with improvements in photography
Optimization was executed by CODE V basically for most aberrations in this system so that it played the role at modulation transfer function (MTF)
We propose an extended optimization method via genetic algorithm specific for chromatic aberration applied to photogrammetry
Summary
Underwater photogrammetry, similar to terrestrial and aerial photogrammetry, has advanced with improvements in photography. Optical aberration greatly reduces the resolving power of conventional optical cameras in waterproof boxes during marine surveying [4]. We removed the conventional outer waterproof box included in the IP67 specification because the glass surface of the box reduces the resolving power of the camera and the penetration of light, and it increases the volume and weight of the camera. Chromatic aberration and focus-point displacement caused by the shift from the shallowwater spectrum to the blue, deep-water spectrum makes universal deep-water photography even more difficult These two optical aberrations reduce the resolving power. Using the optimization method via CODEV and Zemax we developed a novel optical zoom lens applicable in all waters to reduce the volume and weight of the camera by more than 50% and 60%, respectively, and increase its resolving power by 30–40% relative to conventional underwater cameras
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