The S-50 has worked well for me. I've used it with the SeaLife strobe (older version) after removing two of the four screws at the bottom of the WP-DC300 underwater housing. My photos came out great (no small part to the tips I've picked up from this forum).
Don't forget about the "C" mode. My baseline settings (>3 ft) are in the manual mode and the macro settings (<1 ft) are saved in "C". A turn of the knob gets me in close without any hassle.
There are tips for accessing camera functions in the housing and other underwater tips from Canon at the following site: http://web.canon.jp/Imaging/PSS50/PSS50_3000-e.html .
Don't forget about the "C" mode. My baseline settings (>3 ft) are in the manual mode and the macro settings (<1 ft) are saved in "C". A turn of the knob gets me in close without any hassle.
There are tips for accessing camera functions in the housing and other underwater tips from Canon at the following site: http://web.canon.jp/Imaging/PSS50/PSS50_3000-e.html .