The wide angle and zoom lenses you are looking at require a 'barrel tube adapter" to be used on the G15. Canon has a filter adapter and a lens adapter for the G15, which are rather expensive, but work quite well. Bower also makes barrel tube adapters for less, and the fit is about as well as the Canon products.
I use both lens types on my G12, and from experience I will tell you that I am rather disappointed with the wide angle lens. You can expect a bit of distortion at the edges, and you need to make sure you do not zoom with the wide angle, as the distortion may get worse. But if you remove the front part of the lens, you will have a great macro lens to work with. Great for getting bugs and insects without having to be right on top of them.
The zoom lens may present another issue. Because the lens effectively cuts the amount of light entering the camera, the focusing becomes much harder to do using autofocus. Focus times increase quite a bit with any additional lenses on the camera. I opted to stay with the 1.4x lens from Canon, since it keeps the focusing within the capabilities of the camera. Now, the G15 has a much brighter lens, so you may get a better result with a 2.0x lens than I had, but purple fringing at the edges really creeps into the picture. The other issue is that you will need to zoom to maximum to avoid the black edges created from the tube adapter. If you don't, the visible part of the photos will be round!
Overall, these lenses add to the capability of the G series cameras and can make the experience more enjoyable. Have fun!
Steve "Smack53"
