Marine life comes in all sizes from huge to microscopic. If you want to capture the smaller things underwater then you will need a good quality close-up (also called macro) conversion lens. These wet-interchangeable lenses are designed to be used with camera's lens in tele-zoom position. They will cut the minimum focusing distance of the lens and allow you to magnify even the smallest subjects. Most underwater lens manufactures disclose the diopter strength. This number can be roughly used to compare the different lenses magnifying powers. MDC sells both classic close-up lenses like the industry standard Inon UCL-165 M67 and newer kids on the blog such as the Nauticam Compact Macro Converters and the Weefine WFL-03 lenses.