We just finished testing the JVC LS 300's zoom rocker with the Lumix 14-42mm & the 45-140mm power zooms....
First off, the rocker does work with these lenses...yea!......
On both lenses, if you stay in S35 on the mapping section, the 14-42 does vignette in the corners about 3% all the way through the zoom. With the 45-140, it vignettes a little less but is still there. When we re-mapped to MFT,(80%), the 45-140mm is fine but with the 14-42mm it still had a tad of vignette in the lower corners so we had to go down to 78% to clear it.
We are still looking for any other MFT lenses with a power zoom that might work and will report when we find them.

Jim Martin
EVSonline.com

Do you know how the speed of the zoom motor, when controlled by the LS 300, compares when the lens is placed on a Panasonic camera?

I have the Lumix 45-175mm power zoom lens, and when paired with my GH2 the slowest zoom speed is too fast for my taste. I miss the ability to do slow, almost imperceptible zooms with an ENG-style lens (I used to have an HM700 with the Fujinon 17X lens). If you do get a 45-175mm to test, please check the total time it takes to go from one extreme to the other at the slowest speed. (Thanks!)

I'm considering the LS 300 as a hybrid camera for events while keeping my GH series cameras for digital cinema work, and it would be nice to share glass across cameras. Although so far I'm disappointed by the sample footage, especially in the highlights, but I'm hoping that it's just prerelease camera issues and that better-performing profiles can be configured.

When I used the rocker on the right side of the camera, you could control the speed. The small rocker on the handle mad it move fast....but, you have the ability to select the speed in the menu (L,M,H) for both rockers.

Jim Martin
EVSonline.com

Hi. Is there any other lenses (with special adapters) that have push fast auto-focus button and servo zoom and can be used with this cam for, let's say, sports events & weddings ?

Thanks to answer

Hi. Is there any other lenses (with special adapters) that have push fast auto-focus button and servo zoom and can be used with this cam for, let's say, sports events & weddings ?

Thanks to answer

there is the 14-45 power zoom , and the 45-175 power zoom, both for panasonic. in order to get a real zoom and a decent footage at least as good as a cell phone we'll have to spend 5x more for a camcorder. I have the feeling that we will never see a real zoom with servo and AF in M4T . because if they do that then we'd buy (all) a gh4, no?

So I understand that to avoid vignetting you can crop the sensor of the LS300.

Can you still record 4K? Or is it upscaled to 4K?

You will be able to record in 4K down to 80% of scale of the imager. 4K is the actual scan of the image, not an interpolation.