http://www.mirrorlessons.com/2015/02/12/olympus-pro-lenses-wedding-photography-katrin-kullenberg/

Dumb question, but will I need a 4/3 to m4/3 adapter for this lens to work on my GH4?

Thanks

http://toolsandtoys.net/reviews/olympus-12-40mm-f2-8-pro-lens-review/

http://mohamedelbarkani.de/olympus-m-zuiko-12-40mm-f2-8-pro-lens-review/

Love this lens, alongside the Olympus 2.8 40-150 they cover any situation with my AF100/GH2 setup *I saw a link to the firmware updates on the previous page but the linked page doesn't make it clear how/where to download the updates from - any pointers? *ok, my wife is Japanese - she explained things to me :) Cheers

https://www.olympuspassion.com/2017/07/24/heidelberg-olympus-om-d-e-m1-m-zuiko-12-40mm-2-8-pro/

Olympus M.ZUIKO DIGITAL ED 12-40mm F2.8 PRO for $799

https://www.amazon.com/Olympus-Zuiko-Digital-12-40mm-Interchangeable/dp/B00EY3YGBS/

$559 deal at MassDrop

https://www.massdrop.com/buy/olympus-m-zuiko-digital-ed-12-40mm-f-2-8-lens

My review of the Olympus 12-40/2.8, or "a boatload of primes." Spoiler: it is as good or better than what ppl say. I held off buying this lens for any number of reasons. First of all, I had a whole lot of primes in the same range. The Olly 12mm, the Panny 14mm, the Panny 20mm and so on. So it seemed that just in terms of the ideal IQ, I would be paying more money for something that was bigger, heavier, and not as sharp. I used to travel a lot, and hope to travel again, so weight and size are a factor for getting a basic kit in the overhead compartment.
Nonetheless, I was slightly dissatisfied with the sharpness of the 12mm. Maybe I had a bad copy, or maybe it just wasn't as great as ppl say, or whatever. It tests well, but how does it look? And I film mainly events, so the question is also how is the sharpness at medium distance as opposed to close up? And my own testing revealed that in my copy, the 12m prime is sharper at closer distances but not as shapr at medium to long distance.
So, again, looking for the 12mm (think 24mm) "look" I started renting a few lenses. The Panny prime was ever so slightly better. I rented a few zooms. The Leica 12-60 was slightly sharper in the center, but only if you pixel peep, and about the same on the far edges. I didn't care so much for the color on the 12-60. Fine, but nothing special, it looks "coated". Well, the lens is coated, of course.
I tried a few combos with the metabones.
I tried the Panny 12-35 version one and version 2.
I narrowed the list to the Panny 12-35 version one, and the Olly 12-40. The Leica 12-60 was a tough call, but ultimately the color was not, for me personally, the look I wanted. It's a great lens, though. For events, it is actually really helpful to be able to make small zoom adjustments as the stage changes. The Panny version one is sharper than version two, it is smaller, lighter, and has IS built in. For me to choose the Olly, and drag it around, it had to be better.
Having read the reviews, I was annoyed that many of the test results did not agree. Why were the reviews so different? Sharpest at 2.8. Sharpest at 4. Sharpest at 5.6. And on an on.
Well, this lens is better. And, in fact, it is as good as a boatload of primes.
What is sharp? Well, for me, my reference is the Olly 75 mm and the Sigma 56/1.4. These are truly sharp lenses. There's only a few lenses I would call truly sharp.
The Olly 12-40 occasionally drifts into that exotic, truly sharp range. And it usually hovers near it.
I had read that the Olly 12mm was only slightly sharper that the 12-40, so go ahead and buy it because it is so close. Well, in my own testing the 12-140 is sharper. I suspect there is a hesitation amongst pro or serious amateurs to claim a zoom is sharper than a prime. Understandably. And yet, here it is.
At 12mm, the center sharpness is in pixel peep difference compared to the prime. But for anything other than closeups, the 12-40 wins by a fraction of a hair. For closeups, there is no difference. They look the same. But I don't use the 12mm for closeups. Edge sharpness is another story. The 12-40 is better on the edges. It is better than the Panny 12-25. It is better than the Leica 12-60.
And, the color and rendering are excellent.
At 14mm, it is sharper than my Panny 14mm/2.5.
At 20mm it is sharper than my Panny 20mm version one, which BTW is sharper than version two.
Now, the 20mm is a damn fine lens. But it gets beat.
At 25mm the 12-40 is freaky sharp.
Now, as you hit the end of the range, on paper, it looks like there is a drop off, but. actually, it's still very good and in fact as a "portrait" lens at 40mm (think 80mm for a second) it is very good because, in fact, that ever so subtle loss of the clinical look is what you want. So, out goes my Olly 45. I may keep the 42.5, but I don't need both.
So, as I said, a boatload of primes--but, in most cases, better.
For me, it is annoyingly chunky and heavy, but, whatever, the IQ is awesome.
Other things: macro. I had read that the focusing distance is 20cm, so, big deal. But. actually, when you use the lens you can manually focus almost up to the glass (manual gives you a few more mm). Why is that? It's because the 20cm figure is from the focal plane. You get a very nice "semi" macro with this lens, and the quality is really great. Big enough for a bug.
Other things: focus ring. Snap the ring and turn it, you are in manual focus. Super. And, on my G85, it "remembers" so you can pull focus by snapping, setting, unsnap, switch to AF, click focus, snap to pull focus. It sounds like a lot, but it isn't and it is a very cool trick. Noise: no IS, so super silent. MSC motor is smooth and fast. I measured the peak sharpness at 4.5--but the difference between 3.5, 4, 5 and 5.6 was really random.
Bokeh is a mixed bag. With some real distance between the subject and background, at 2.8 the bokeh is superb. With a busy background, and a closer background, the bokeh is a bit cluttered. At 35-40, if you are shooting a portrait, it is lovely with a distant background. At 12mm, well, it looks like 12mm.
What does a prime do better? In high contrast scenes, on the edge of the image the primes tend to handle chromatic aberration better. Extra plus: It's built like a tank, is somewhat sealed and has a reversible hood.
Photo: wide open, F2.8 at full extension (40mm) shows the soft blur bokeh.