Disclosure: I work for Gates Underwater Products
Mark is correct in his assessment. The SWP44 is designed for very specific cameras/chip sizes like the FX1/Z1 and HVX200. It is not compatible with the FX7/V1 cameras as the internal optics are very different. The SWP44 would be very soft if used with that camera.
By analogy, you couldn't wear a friends prescription glasses unless you happen to have exactly the same eyesight. Video cameras are the same, and have widely varying 'eyesight'.
Simple ports like the FP44 flat and SP44 dome work with just about any camera as they are simple. The SWP44 is at the other end of the spectrum. It is a converter lens (meaning it provides wide angle coverage and retains full zoom capability), providing sharp, distortion free images. This type of performance must be matched to the camera for which it is designed.
Cheers.
John