Nikon D5100 Movie recording?

I was wondering if you could help i have a d5100 nikon and when i film movies it doesn't forcus on the main object it goes blury and the backgrund is clear don't understand why.

Your focus point is off.

Personally, I don't believe in using a still camera for video, or a camcorder for still shots.
Each have their place, each do best at their INTENDED use.

If it was a photo, I'd say you should use only the center focal point, half press, then re-compose as required.

For video, I would be using my camcorder.

P.S. Don't use the word "film"… You are talking about a DIGITAL camera.

Most people shoot video using manual focus.

This is what they use

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

While some Nikon cameras can auto-focus when in the live view mode, that process is much slower that when shooting still and sometimes you can get what is called auto-focus pumping while the camera attempts to find the focus point

As mentioned above, if you really want to shoot video, buy a video camera.

What you need to know about using a still camera to shoot video

http://www.luminous-landscape.com/techniques/3_years_later_dslr_video_one_mans_perspective.shtml

This video tutorial might help: http://www.nikondigitutor.com/eng/d5100/index.html