[PMA] Panasonic SLR Camera Reflects Difficulty of AF Development

Mar 11, 2009
Tomohiro Otsuki, Nikkei Electronics
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Panasonic Corp exhibited its lens-interchangeable camera "DMC-GH1," which will be released by the end of July 2009, at the Photo Marketing Association (PMA) show.

The camera can record HD video in 1080/24p or 720/60p AVCHD format. And it can output 1080/60i video on a TV when decoding (replaying) HD video, according to the company. The SoC hardware to improve image quality and the image sensor's pixel structure in the DMC-GH1 are the same as those seen in the DMC-G1.

The DMC-GH1 (prototype) has an auto focus (AF) video recording function that users might find strange. Specifically, the AF function does not work when the zoom ring is turned after the video button is pressed.

There are two methods of avoiding this problem.

(1) Focusing the camera on the subject by half-pressing the shutter button after rotating the zoom ring.

(2) Presetting the AF mode dial on the upper left hand side of the camera body to AFC mode (which continuously focuses on different subjects like a camcorder) before pressing the video button.

In other words, the first method uses AFS (auto focus-single) mode (in which the camera focuses on the subject only when the shutter button is pressed), which is useful for doing things like filming a movie. For example, to produce a movie effect, it is possible to focus on a man in the foreground while he is speaking and shift the focus to a woman in the background as she starts speaking.

On the other hand, this mode is not suited for following and shooting a running child using the zoom function, for example.

Though the second method is effective in such a case, still camera users usually shoot images in AFS mode. So, they have to remember to switch the AF mode dial to AFC before pressing the video button. As far as I could tell from the exhibited model, however, the camera's focus in AFC mode did not seem very accurate.

If the trouble of switching the dial causes a negative user experience, what must be done is very clear. It is to automatically switch the mode to AFC when the video button is pressed, even though the AF mode dial indicates AFS. And Panasonic should tell users that the AF mode dial can be used only for still images.

When I asked Panasonic at its booth if it is planning to add a function to automatically switch to AFC mode, the company gave me two different responses. One person denied it. But another neither confirmed nor denied it, just saying the camera is still under development.

I don't know which is the case. But supplementary explanation of the first person was interesting because it was about the difficulty of the development of the unprecedented auto focus function.

First, the DMC-GH1 is equipped with a 4/3-inch image sensor. And it has a much shallower depth of field than, for example, broadcast cameras with a 2/3-inch image sensor. Therefore, it is difficult for the camera to automatically continue to focus on the moving subject and shoot a movie that does not make viewers feel uncomfortable.

Moreover, Panasonic developed the AF capability of the DMC-GH1 based on the DMC-G1's AF function, which can be used only for taking still pictures. The DMC-G1's AF is very accurate in AFS mode, and it was realized through sudden focus shifts and slight camera shakes. So, this is possible only with still images.

It will take more time for Panasonic to eliminate the problems caused by such motions and achieve a high focus accuracy in AFC mode, said the person who denied the possibility that the company will enable the camera to automatically switch to AFC mode.