Optical Considerations: Field of View

With subsea imaging, water itself has to be taken into account as part of the lens system. Water has a refractive index of 1.33. Sea water is similar but has a lot of variability with depth, salinity and other dissolved elements.

The water lens interface causes magnification up to 33%. The field of view (FOV) of the image is reduced because of the magnification effect. Water-corrected lenses return the geometry of the image to an in-air equivalent. An 80° FOV lens would be reduced to less than 60° with a simple flat acrylic port.