Normally, the camera uses the whole imaging sensor during video, and scales the output down to 1920x1080 pixels for the video stream. In ETC mode, though, it only uses the central 1920x1080 pixels of the sensor, giving an effective 2.4× crop factor, while retaining the full resolution, see the image below:
You can enable the ETC mode in the video options menu, here:
With ETC mode enabled, all the other features of the camera also function, like the autofocus and Optical Image Stabilization (OIS). Let's say that you use the Lumix G 20mm f/1.7 pancake lens. When using ETC during video recording, it effectively becomes 48mm f/1.7, with 48mm = 20mm × 2.4. Which can be useful at times.
Using ETC gives you a tighter crop, while retaining the true 1920x1080 pixel resolution. However, one can speculate that the image quality might suffer, as the camera cannot average over a larger number of pixels when composing each video frame. I will test the video quality in this article.
To test the ETC mode, I have used a couple of zoom lenses with around 3x zoom range. That way, I can get the same field of view when I use the lens in the long position, and when I use the lens in the short position with ETC enabled.
I used the Lumix X 45-175mm f/4-5.6 lens at 175mm and 71mm + ETC, and the Lumix G 12-32mm f/3.5-5.6 at 32mm and 13mm + ETC.
Here are the test results:
I used the 1080p mode, 25 FPS, and set the ISO to 200, 800, and 3200.
What we see here, is that there is more noise when using ETC. But the ETC video stream holds up pretty well. Only at ISO 3200 does it border on unacceptable. And this is quite impressive performance. When I tested the Lumix GH3 in the same way, it did not perform as well.
Even if I have set the same image and video parameters in both cameras, the GM1 appears to apply more noise reduction. And it appears to work quite well!
Here are a couple of example videos, one using ETC, and the other not. Both were recorded in a rather dark concert venue. I used the Lumix G 12-32mm f/3.5-5.6 on the Lumix GM1 camera.
Without ETC, 32mm f/5.6, ISO 6400, 25FPS, 1/25s:
With ETC, 13mm f/3.6, ISO 6400, 25FPS, 1/25s:
Normally, ISO 3200 is the maximum for video use with the Lumix GM1. However, with a strange trick, you can get it up to 6400. If you use the Creative Movie Mode (film camera icon on the top plate mode dial), you can set the S exposure mode. Set the shutter speed to 1/25s (or 1/30s if you have an NTSC version of the camera).
Then, you can apply exposure compensation. Up to +2, nothing happens. However, between +2 and +3, you get one more stop of gain, corresponding to ISO 6400.
Again, we see that the video done with ETC is much more noisy. So the lesson is: Don't use ETC unless you have to!
The ETC mode is a very useful feature, but it is best used at low ISO. At higher ISO, the video quality will suffer. However, the Lumix GM1 appears to give more clean ETC video output than the Lumix GH3, which was certainly not what I had expected.
When using ETC with a long lens, you can get an extreme tele reach. In the example below, I am using the Lumix G 100-300mm f/4-5.6 at 300mm, together with the ETC mode. This gives a very compressed perspective, due to the extreme tele effect.
You'll see the image wobbling. This is due to atmospheric disturbances, since the light travels through a lot of air before it reaches the camera. There is no way to avoid this, beyond, perhaps, getting up early in the morning while the air is cooler.
When using the Lumix G 100-300mm lens at 300mm, and with ETC, the effective equivalent focal length becomes 1500mm, which is a lot. Even when placing the camera on a tripod, I had to remove the first seconds of video footage while waiting for the camera and lens to settle down after pressing the shutter button.