Zooming in and out during video mode on Nikon D3100?

I want to buy a Nikon d3100 mainly because it has excellent image quality and has video mode as well. My question is though, while in video mode, if I zoom in/out how long does it usually take the camera to focus? Or would I have to focus it manually?

If you are shooting video using ANY camera, you pre-focus the lens, frame the shot and shoot the scene. You will be doing this for each scene as you follow your script.

I get the sneaky felling that you are shooting some kind of stream of conscienceless video where you just walk around shooting whatever tickles your fancy.

The auto focus on the Nikon D3100 when in the video mode is slower than the ultra fast auto-focusing AF-S lenses. That is because you have to use live view to shoot video.

Here is what people use to assure sharp focus when trying to use a dSLR as a video camera

http://www.luminous-landscape.com/reviews/accessories/hoodloupe-3.shtml

But what you really need to know is this

http://www.luminous-landscape.com/reviews/camcorders/cam-cam.shtml

Actually the D3200 may be a better camera for you.

http://www.dxomark.com/...nd2)/Nikon

For recording video, you should buy an actual video camera/camcorder. Despite popular belief, DSLRs are not replacements for actual camcorders and do NOT offer better video quality than actual camcorders. If DSLRs are better than camcorders, don't you think camcorders would out of production? Hmm, but guess what, they're still being produced. DSLRs are designed to take stills; their manufacturers have added video features to them so uninformed people buy them to record videos. AND the type of AF used during live use is slow and lousy.