Video Camera Focus

First of all, locate the focus control. Professional cameras usually have a manual focus ring near the front of the lens housing. Consumer-level cameras usually have a small dial (Note: you may need to select "manual focus" from the menu).

1. Make sure the camera is set to manual focus.
2. Zoom in as tight as you can on the subject you wish to focus on.
3. Adjust the focus ring until the picture is sharp. Turn the ring clockwise for closer focus, anti-clockwise for more distant focus.
4. Zoom out to the required framing — the picture should stay nice and sharp.
5. If the picture loses focus when zoomed out, check the back-focus and make sure the macro focus is not engaged.

If you need to adjust your focus on the fly (for example, you're in the middle of shooting the Prime Minister's speech when you realise her face is soft), it helps to know which way to turn the focus ring. If you go the wrong way and defocus more, even if you correct yourself quickly you've drawn attention to your camera work. Try comparing the background and foreground focus. If the background is sharper than the subject, then you need to pull focus to a closer point (and vice versa).

Note: You will usually find the sharpest focus occurs at about the middle iris position.

Difficult Focus Conditions

You'll notice that focusing is more difficult in certain conditions. Basically, the more light coming through the lens, the easier it is to focus (this is related to depth of field). Obviously it will be more difficult to focus in very low light. If you're really struggling with low-light focus, and you can't add more lighting, try these things:

* Make sure your shutter is turned off.
* If your camera has a filter wheel, make sure you're using the correct low-light filter. Remove any add-on filters.
* If your camera has a digital gain function, try adding a little gain (note: this compromises picture quality).
* Stay zoomed as wide as possible. If your lens has a 2X extender, make sure it's on 1X.

source : source : http://www.mediacollege.com