You can't do any pinch to zoom on the iPhone 4S with iOS 5 for videos. It only works for still shots. Probably due to the fact that the real time 1080P recording already requires a boat load of CPU time and adding zooming would require each frame to be sampled and resized on the fly which would add a huge amount of overhead.
There are various schemes for adding lenses to the iPhone 4S, and earlier models. Among the inexpensive solutions, the Macro lenses, in a very few instances, give adequate quality. Fewer Wide Angle lenes offered have adequate result. The attempts at inexpensive Zoom lenses are the poorest of the quality I have found.
Ther are some schemes for attaching high quality lenses meant for more expensive cameras. Since, I do not have a collection of lensescacquired over the years, this approach is not a reasonable option for me. If you have a selection of zoom lenses for other cameras, that might be an approach for you to consider.
Faced with what I have found so far, I am waiting for the more powerful processors, and possibly even better camera and lens combinations built in to the iPhone 5 and the iPad 3 for the possibility of video zoom built in.
