Nemrod:
Although one can put both 67mm and AD mount lenses on the housing, I think it is fair to say that for several of the available wide lenses, sharpness and vignetting are at least unknown and according to some owners, may be undesirable. It APPEARS to me that with some choices, by the time one zooms in enough to avoid vignetting, most of the benefit of the lens is lost, leaving the user with a very big dome that is really no wider than a much smaller wide lens.
You make good points, I am not picking a fight either but I also like to stay based in facts and this statement is not true at all and over and over I have posted various photos demonstrating the results. The dome lenses, be it the 100WAL or 165AD produce significantly wider FOV than the native flat port and there is evidence to indicate that they are at least as wide if not wider than the Fisheye-04. I have measured the 100WAL plus dome at 125 degrees diagonal and the 165AD at approximately 155 degrees diagonal and both are sharp, as sharp as they would be on any other camera for which they are alleged to work and I do have a Canon 570IS with both Ike and OEM housings and an Oly with the Inon AD fisheye adapter and appropriate adapters to make direct comparisons and have. The FIX shoots as wide and as sharp, actually more so in terms of quality as you might expect from a more advanced camera, the dynamic range is clearly superior based on my now direct experience.
I think the Ikelite housing is a cost effective compromise, for me, my opinion, based on what I know, the OEM is definitely the least desirable option. The only wide angle lens that is known to work with it, per Inon, is the WAL100-28AD and when you add the dome that is an eight hundred dollars lens and the fact is the WAL100-28AD with dome vignettes naturally per Inon and requires a 95% crop from the get go.
As to which housing is best or most effective, personal needs are paramount, some might say something is better than nothing and others like me might say nothing is better than something which cannot accomplish the requirements, my requirements, to the extent other's requirements differ, please of course adjust your decision process to reflect that. I have said that many times.
"OEM gland", the controls that pass through the housings are routinely referred to as a gland and the OEM means or meant as I intended, original manufacturer, being Canon supplied.
You are right, I don't feel inspired with confidence by my Canon DC-12 housing based on my experiences with it.
I also fully agree, most floods are user generated due to poor practices and contaminates etc as you have stated, exactly right, yes, that said, the Canon housing is not a confidence builder for me and the other limitations imposed in this application make it a no brainier, none purchase for me.
People like to (budget) high end a dSLR and low end a P&S and maybe that is why there is a limited number of middle ground options.
N