Here is a little Triplefin taken on snorkle at Island Bay, Wellington, New Zealand. Taken with a Olympus C-7070 in an Ikelite housing, Mode - Super Macro, Strobe - can't afford one yet!
Allows keeping same subject size in the LCD monitor as if you were at 1cm from the subject. Rear male base screw 46mm. Allows a 1/1 ratio at 20cm from the subject.
This article will hopefully be of interest to divers considering a career in commercial diving or wishing to complete a commercial course for other reasons. Hopefully it will give you a bit of an insight into what to expect.