So – wouldn't it be great if we could have a large sensor, but with only about 2 million pixels? No artifacts, right? Indeed the new Sony CineAlta F3 offers just that, though at a mere US $23,000 with three lens set.
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But how about something a bit less expensive – say, the just released Panasonic GH2, which sells for less than $1,000 (body only)?
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Indeed something very much like this is the case, though Panasonic seems to have gone out of its way to hide the existence of this exciting new feature
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Consequently what we see is that in ETC mode at ISO 160, and up to 320, there is no discernible noise degradation visible. This is likely because the GH2 is so clean at low ISOs to begin with. Above ISO 320 in ETC mode images are somewhat noisier than full raster images. I would judge about one to two IE noisier, mostly visible in the shadows and quarter tones. Given that this appears to be the only downside of ETC video mode, it's a small price to pay.
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ETC (Extra Tele Conv) video mode on the Panasonic GH2 is indeed a free lunch. One gets a built-in 2.6X teleconverter, with no light loss and no image quality loss, by simply pressing a button. Bon appetit.