In addition to being inconvenient, testing underwater lenses in their normal environment involves the difficulty of differentiating between the effects caused by the photographic system and those caused by the turbidity of the water. The principles developed and practical devices illustrated show that it is possible to apply all test methods for common photographic lenses to underwater lenses with a correctly designed concentric telescopic meniscus.
W. Mandler, "A Concentric Telescopic Meniscus for Testing Underwater Lenses," Appl. Opt. 9, 771-774 (1970)