Check out "Woody's Diopter"

Here is an image from Nexusamerica.com website:

It's a removable closeup lens for macro work. UW film shooters have been using it for a while and they seem to love it. People looking for more versatility for shooting an underwater DSLR setup might want to give it a try. I'm going to. They make models for Ike ports and Nexus ports

See this page for details:

http://www.nexusamerica.com/Misc/Misc.html

Cheers

James

I've had one of these for my Canon EOS A2 Ikelite housing for a while. Works well. Not a huge amount of magnification (something like 8% to 15% depending on the other things he stacked up on his lens along with it), but it does help. Barry Lipman has some examples of how effective this little trinket is on his site:

http://www.barrylipman.com/diopt.htm

Mike

Used to use one on my old housed system and DM John has one he uses on his Fuji S2Pro. Isn't bad - does in a pinch. Personally I prefer using true diopters on the lens, but hey. Even if you find they are not for you, they make a nice port cover :-)

M