Hi Mike
There is a housing for the IXUS 55, but it is rated to only 3m, which of course is not very useful for diving.
For the housing for the IXUS 60 to fit the IXUS 55, the dimensions of the camera would have to be exactly the same, as well as the positions of all the controls. It is possible that the IXUS 55 would fit in the housing for the IXUS 60, but you may not be able to operate all the controls. Obviously, you need to be able to operate the shutter button at the absolute minimum. It would probably be good to be able to operate the mode switch on the camera, and possibly to zoom (although I find I very rarely use the zoom on my camera when underwater; its is easier/better to ‘zoom with your fins’!). I’m not sure what other controls the IXUS 55 has - I suspect it doesn’t have manual or semi-automatic modes (M, Av, Tv), but it probably has an exposure adjust mode, which would also be useful underwater. Similarly being able to switch in and out of macro mode would be useful underwater. If you can’t do these things, you would probably find the underwater photography experience somewhat frustrating.
In general, when Canon have a housing that fits a camera, they publicise it. An example is the WP-DC8 which worked for both the A640 and A630. Canon did not try to hide the fact that the A630 fitted in the WP-DC8 in the hope that A630 owners would upgrade to the A640. Canon don’t seem to indicate that the IXUS60 housing will operate with the IXUS55, so unfortunately, I think you will find that there is a good reason why: i.e. that the IXUS 55 doesn’t fit, or at least some of the controls can’t be accessed.
I can certainly understand your lack of enthusiasm to buy a new camera, however if you are going to get into underwater photography beyond taking the occasional shot underwater, you will probably find that you will want a more feature rich camera after a few dives with your IXUS.
regards
