I put together a quick video using the Sony Nex-5n and the 16mm f/2.8 lens to show you what happens when your add on the conversion lenses. I mounted them on the 16mm lens while recording so you can see exactly what they do!
The Wide angle conversion lens turns the 16mm lens (24mm effective focal length) to an effective focal length of 18mm. The Fisheye Conversion lens turns the 16mm (24mm effective) into an effective 15mm!! Very wide and a really nice effect if your into fisheye lenses. They are a Love/Hate relationship I notice due to the heavy distortion, but I think it’s cool on symmetrical compositions in particular!
If your not understanding the effective focal length jargon, it’s because of the Crop Factor. The sensor not being a true 35mm size is were the crop factor comes from. Full frame sensors have no crop factor associated with them. Whatever the lens focal length says, it is! Smaller than 35mm or Full Frame, and you need to apply the “crop factor” to the focal length in order to get the Effective focal length. I have a full tutorial on Crop Factors over Here that explains it all in depth!