Hi Pakman, yes of course OEM housings have a fixed port and that may be their 'undoing' when applying this modification. As I understand it, purpose of the G9 Ikelite short port is not so much to avoid vignetting (though I'm sure it does) but to place the optics in a 'correct' relationship. As an Ikelite owner, I won't be researching this one, but OEM owners will appreciate the 'heads up'.
OEM housings are normally well catered for by Sea & Sea who supply push fit adaptors for their Motor Marine I compatible w/a glass - 17mm and 20mm. I used such a setup on my point and shoot Pentax Optio before I circummed to this madness...

