One of the cool features of the GH2 is the video mode called EX Tele Conv (ETC). Basically the camera is only using the center of the camera's CMOS sensor and cropping it to either 1920 x 1080 or 1280 x 720 pixels depending on the HD mode selected. When shooting in 1920X1080 HD mode and when ETC mode is engaged, the GH2's 4608 x 3456 sensor is “cropped” to 1920X1080. In other words, only the central 2 Megapixels of the sensor's overall 18 Megapixels is recorded. This is a 1 to 1 radio of the pixels on the chip.
It does wonders for my Nikkor *ED 400mm telephoto lens. There are positive implications: no line skipping, binning, or digital interpolation are needed. It's as if the sensor was only 2MP rather than 18MP. As a consequence the image recorded has a crop factor of 2.6X over the full Micro Four Thirds format, a format that already produces a 2X field of view as compared to full frame 35mm. This means that in ETC video mode the focal length marked on the lens is actually 5.2X what it would be in full-frame 35mm terms. So my long lens, the Nikkor 400mm lens has an equivalent a 2,080mm lens in Extra Tele Conv video mode.
As a consequence, any lens I put on the GH2 when shot in ETC video mode has an effective focal length of 2.6X of what's marked on the barrel, with no loss of light and video quality! It's like shooting with a 2.6X teleconverter but without the image quality loss and without the light loss.
The other benefit of this mode is that smaller 16mm lenses can be used with now light fall off. I have not done this.
Here are some birds I found today around Sequim, WA. I shot both 1080p and 720p. The last two shots shows the difference from not using ETC and using ETC. Edited in FCPX.