http://www.pekkapotka.com/journal/2013/10/26/e-m1-with-mzuiko-12-40mm-f28-pro-the-first-session.html

This looks like a really great lens, better than the Panny 12-35mm in terms of weather seal, the extra focal length, and lower price. The image quality seems to be equal. The lack of OIS is not an issue for me, as i always use a tripod for videos.

The most important question for me is, is this lens parfocal? Does anybody know?

Btw, lens is available at http://www.ebay.com/itm/ws/eBayISAPI.dll?ViewItem&item=200992046723

http://camera.itmedia.co.jp/dc/articles/1311/22/news066.html

The Olympus 12-40 mm f/2.8 is such a good lens that shows that you can make professional-quality pictures with the micro-43 system. Our testing shows that this robust, dust- and splash-proof micro-43 zoom lens can be a high-quality alternative for a much larger and more expensive 24-70 mm f/2.8 zoom lens. The sharpness starting at f/2.8 is already very high from center to the extreme corners.

http://www.camerastuffreview.com/olympus-lens-review/olympus-12-40mm28-review

For those that wonder about it's usefulness on a GH2 for video, I've tried it, and with lens gears on it for zooming, it actually works pretty well once you get used to its querks.

Since it is not a fully manual zoom, you will feel a sort of electronic servo happening whilst zooming with a follow focus, and sometimes the zoom in and out will not be as smooth as a fully manual zoom. The autofocus works good most of the time, sometimes it will hunt for focus in low light conditions especially when zoomed in, and fail. Another thing to note is when in AF and zooming in, it will loose focus when you get to 40mm, and find it again right afterwards. This is a bummer if you are tracking someone or something, so try to avoid that approach. Zooming out it stays in focus.

I've since sold the lens, and half regretting it! I might get it again in the future...

Here's a photo of it with my GH2 setup.

http://www.optyczne.pl/313.1-Test_obiektywu-Olympus_M.Zuiko_Digital_12-40_mm_f_2.8_ED_PRO_Wstęp.html

Test at FN (mostly DXOMark repetition)

http://www.focus-numerique.com/test-1777/objectif-test-olympus-12-40-mm-f28-presentation-caracteristiques-1.html

The optical quality of this standard zoom is impressive, with an extremely sharp centre zone whereas the border and corner resolution is very good. This perception is once more leveraged by the low amount of lateral CAs. Furthermore the distortion level is fine from a user perspective, but technically it relies on a drastic amount of auto-correction by the system or a RAW-converter - especially at 12mm wide-open.

http://www.photozone.de/m43/862_oly1240

+1 what @den59 asked.

This lens delivers outstanding sharpness through much of the zoom range at maximum aperture and sports a robust, dust and splash proof build, all while remaining compact and lightweight. The excellent performance of this lens will certainly win it many fans, that's for sure.

http://www.ephotozine.com/article/olympus-m-zuiko-ed-12-40mm-f-2-8-pro-lens-review-24513

@den59 @CFreak No image flicker that I can see during zoom in or out. It may also be parfocal as the focus seems to remain sharp while zooming in manual focus mode.