I just tested this on the GH4 with peaking enabled and it is definitely parfocal in manual focus mode with no annoying jitters during zoom forward or back. For just a few millimeters in between 30-40mm it softens ever so slightly, but it's really unnoticeable unless you're pixel peeping frame by frame. I'm kind of thrilled, it should work awesome for whip or creeping zooms - no need to rent a cinema lens to get the same effect (unless you need a longer reach).

@Tron How is it's speed in autofocus mode? I remember some early test videos showing the Pana 12-35 was really fast to autofocus on the GH3. Is that also the case with the Oly 12-40 (on the GH4)?

@Tron Thanks!

http://www.digitalcamerareview.com/shared/picture.asp?f=56987

@Tron

I am a Nikon shooter so most of my glass is full frame glass. I want at least one zoom for M/43 that is native glass but I have some concerns. My concern is the focus by wire mechanism on all of the M/43 glass. I had and sold the 14mm 2.5 and will likely sell my Panny 20mm 1.7 as well due to the small size (follow focus issues) but mainly the focus by wire mechanism. How is the manual focus on this lens? I read that it has hard stops in manual focus mode, that being said how does it feel with a follow focus. I plan to use this with my GH4 as well as the GH2's and a AF100 if that makes any difference.

@mat33

Thanks for the input and feedback. I am vacillating back and forth between losing OIS with the Panasonic 12-35 or having the Olympus 12-40 which seems to be a better lens overall with a better build quality and manual focus mechanism. This is a very hard decision but more than likely I will purchase the Olympus due to the focus mechanism and what I perceive to be a better build over the Panasonic lens. I am a stickler for build quality and the Olympus seems to have that in spades.

I do think that the M.Zuiko 12-40mm F2.8 Pro lens is a great lens, suitable to be used by anyone.

If you have bought an OM-D system, and intend to have a high grade lens, just one lens to cover most of your shooting needs, this 12-40mm Pro lens should be in your consideration. It is versatile, does close up shooting well, and is sufficiently wide for most situations at 12mm focal length. That F2.8 bright constant aperture is also useful in many situations.

http://robinwong.blogspot.ru/2014/07/olympus-mzuiko-12-40mm-f28-pro-lens_6.html

I use it manually with follow focus and zoom with zip gears. Focus is definitely repeatable, zoom can always be smoother, but is better than the Panasonic 12-35. I do not see sudden exposure changes when zooming in and out as some tests online show.

@crazypete Thanks! There were a lot of conflicting reports of stepping in the manual focus process but I suspected the complaints where for those who didn't know about the focus ring clutching when slid back

anyone coupled this lens with a LA7200?

New firmware

http://www.olympus.co.jp/jp/support/cs/dslr/fw/index.html#mzd

The Olympus 12-40mm f/2.8 is a lens that fills a need for a lot of shooters, and I’m happy to report it does so with excellent quality. The lens is simply brilliantly sharp across the frame right from wide open and at all focal lengths. It’s really hard to ask more from a zoom. It might be the overall sharpest standard zoom I’ve had the pleasure to use.

http://admiringlight.com/blog/review-olympus-12-40mm-f2-8-pro/