So back to my original question, does anybody have any suggestions or info about lenses and lens ports for an Ikelite housing with a Canon 7D camera?
The 15-85mm lens has a 3.2" diameter. The maximum diameter that physically fits an Ikelite port is 3.3" but since a zoom lens needs space for gears I think it may not work for the 15-85mm. Here is the blurb from the Ikelite website.
Maximum lens diameter is limited to 8.4cm (3.3"). Lenses up to 7.1cm (2.8") allow attachment of the standard zoom and clamp set. Larger diameter lenses require the special #5509.28 zoom and clamp set, included with all Ikelite dSLR housings.
You can find more info on this wide-lens gear here and as best I can see it works up to 3". I certainly would check with Ikelite or someone who has the actual hardware to test it out before getting the 15-85.
Finally, at the risk of becoming annoying, really think if this is the right time to make the jump. In addition to the points raised earlier, if your budget is already stretched, getting a housing with ports sets you back another $1500 or more. You don't mention a strobe but if you have to add that plus arms sync cords etc, add another $600-1000 or so. Adding a strobe to your P&S probably will do your UW images more good then going from P&S to dSLR with no strobes and is somewhat less distracting from diving than a full dSLR setup.
Bart