Friday, 18 May 2012

300mm plus ETC gives an enormous reach!

The Lumix G 100-300mm tele zoom lens is a very long one, useful for birds, wildlife, events, sports, and so on. When recording video with the Panasonic GH2, you can use the ETC, Extended Tele Converter mode, which uses the centre of the sensor only, for an additional 2.6x factor on the effective focal length. At 300mm, this gives a staggering 1560mm equivalent focal length, when comparing with the traditional 35mm film format.

I have made some example video clips at 300mm, including the 2.6x ETC mode. The following video contains four segments, from the May 17th Constitution Day parade in Oslo. Notice that with the 1560mm effective focal length, the perspective is very compressed.



A stable tripod is needed. My tripod is not too stable, and just pressing the button made the video wobble. So the first seconds of footage was always unusable, while the camera and lens settled down.

Notice how the video flickers quite a bit, especially in clip number two and three. This is due to atmospheric disturbances. All the people in the parade generate heat, and it affects the path of the light. The first clip is from the very start of the parade, and the air is much more calm.

This can be seen in still images as well. Here is an image taken from the same point with f=300mm, ISO 160, 1/200s, f/7.1, tripod mounted:


An 1:1 crop of the centre of the image illustrates the blurring caused by the atmospheric disturbances even better:


Please note that this blurring could not have been fixed by the usual measures: Lower ISO, faster shutter speed, smaller aperture, tripod, or even a better lens. It is simply a physical phenomenon which affects an image when the light travels a long distance across air with different temperatures. The only ways to avoid it would be to move closer, or to take the image when the air is more neutral, possibly early morning. But in this case, I wanted the compressed perspective, and rising early was not an option since the parade had not started at that time.

In my review of the tele zoom lens, I noted that it loses a bit of contrast at 300mm in strong sun light, due to flare. I think this happens in my example video as well. It could have been corrected a bit by adjusting the curves in the video, but I left it as is.

Conclusion

The ETC mode, when combined with a long lens, allows for a very significant reach for videos, and a very compressed perspective. However, be sure to have a stable tripod, and beware that atmospheric disturbances may make your video footage less usable.



5 comments:

  1. I think a faster shutter speed should resolve in less disturbance, since the time the disturbances are recorded is reduced.

    If you take a picture of water in motion, the faster the shutter speed, the less movement you record.

    The same goes for air that is in motion.

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    1. Not really, it is like you are taking a picture through wobbly glass.That is why they have to go high up with astronomical telescopes. It can only be fixed for still subjects like stars by small adjustments on the mirror.

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    2. Yes, this is right. The only way to get rid of this problem is to go closer, or to get rid of the atmosphere, the latter being quite difficult for most people ...

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  2. I love the ETC mode on the GH2. A question I often wonder is if it is better to shoot in the middle of the zoom range where it is sharpest with ETC on, or at the extreme on the zoom...

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    1. In terms of video image quality, I think it is almost always best to avoid ETC if you can. Of course, it depends on the lens, and just how unsharp it is in the longest end. But my experiments show that there is significantly more noise when using ETC.

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