Despite reading so many reviews and watching countless youtube videos, I missed the reports of the jitter problem with some copies of this lens. I noticed it on my own when shooting with my GH4 and it's really a pretty bad problem rendering a lot of footage useless. I also have a 12-35 and I tested both lenses at 35mm handheld and the difference is night and day. I'm travelling in Thailand (got the lens here too) and I plan to walk into a service center in a couple weeks when I'm in bangkok. I really hope the problem can be fixed otherwise I'll have to sell the lens. It works find for stills but for video it's only really with IS switched off and that won't work for me. But then again what will be my next option? I really hope panasonic will fix or replace my lens. If anyone is interested in seeing my test footage, I can upload it.