Last year Nikon filed a patent application #20100110236 for an autofocus in a video/TV camera with interchangeable lenses. Here are some quoted text from the patent application- note that they used the word "inexpensive":
"The present invention relates to an autofocus apparatus and a camera that are used for a camera, mainly for a video camera and particularly for a TV camera. The present invention also relates to a lens barrel and a camera that are used chiefly for a lens interchangeable type video camera and particularly for a lens interchangeable type TV camera.
There have hitherto been two kinds of autofocus apparatuses as an autofocus apparatus for a camera. One type is generally called a crest climbing type autofocus apparatus used for mainly a video camera. The other type is called an image deviation type autofocus apparatus employed for chiefly a still camera. The two types of autofocus apparatuses will hereinafter be described with reference to the drawings.
It is a primary object of the present invention, which was contrived under such circumstances, to provide an autofocus apparatus, a camera and a lens barrel that are inexpensive and capable of focusing quickly with a high accuracy.
It is another object of the present invention to provide a lens barrel capable of actualizing an autofocus function even when attached to a camera body incorporating no autofocus function.
It is a further object of the present invention to provide an autofocus apparatus capable of focusing on a photographing target at a high efficiency."