Olympus M Zuiko 12-40mm f2.8 Pro came out in 2013 alongside the E-M1 mark 1. The lens has received many rave reviews and after 5 years of resisting its allure, I've finally given in. It's not without good reason. I've owned the already excellent, but older Zuiko 12-60mm f2.8-4 from the defunct 43 DSLR system and the lens still delivers good results via an adapter on m43 cameras. But the lens AF with contrast detect of modern cameras is a slow combination and the 12-60 is front heavy on your typical, more nibble m43 cameras.
The old and the new.
But before we get ahead of ourselves, what is this hyped 12-40 (or the old 12-60 for that matter) supposed to be about? It's a general purpose zoom lens, wide enough to shoot landscapes and architecture and can zoom enough to create some pleasing portrait shots. It's the kind of lens that is most likely to be constantly attached to your camera. These zooms have a similar range as the usual kit zooms often sold with interchangeable cameras, but the image quality is noticeably better, they also suck in more light for more low light situations so they cost and weigh more as a result.
The 12-40 comes in an all-black box and packaging and it is first rate like many Olympus products in recent years. It makes you look forward to whatever is inside.
Nothing wrong with casual shooting.
The lens itself gives a similar first impression as I had with the 12-60 a decade ago: smooth, solid and reassuring. It feels like a younger sibling of the older lens. It is by no means a small lens though, even by m43 standards, but I find it's about as long as the M. Zuiko 14-150 II zoom lens, only thicker and slightly heavier. In practice, on my main EM5 markII camera, it is still a bit front heavy, but it's lighter and smaller than my old 12-60. Having no extra lens adapter helps too. Good.
Like the classic 12-60, the 12-40 offers weather-sealing (granted your lens is attached to a weather-sealed body too). I think most photographers have shot with non-weather-sealed camera/lens in rain and/or snow and got away with it just fine. I think here the difference is that it offers peace of mind. Rather than hiding the camera in rain and only taking it out quickly for a few shots and then hide it again. This one you can just let it dangle around your neck, no matter the weather and shoot when needed. I think it reinforces its "all purpose" quality. For me at least, that type of convenience is great. Furthermore, if you don't fear your camera/lens is going to break after a few splashes, you will be tempted to shoot in challenging environments, increasing the odds of you getting that special shot.
Get wet. And get the shot.
Another big selling point of the 12-40 lens is the constant aperture, in stark contrast to your typical kit zoom. So, whether if it's 12mm or all the way to 40mm, your max aperture will remain f/2.8 (or whatever other aperture you choose). This has many advantages. It means your exposure settings can remain the same no matter the focal lenght. This becomes particularly evident when shooting video where zooming doesn't create a dimming effect. Furthermore, with kit zooms, you instinctively stick to the wider focal lenghts to keep as much light as possible when shooting stills. With the 12-40, this is a non-issue. And of course, if your constant aperture zoom lens sucks in more light, you have more artistic possibilities to isolate (or not) your subjects, at any focal lenght.
My old 12-60 lens has a classic manual focus override like many DSLR lenses which I've always liked. The newer 12-40 has that infinite, imprecise, focus-by-wire of many m43 and other mirrorless system lenses. Meh... Until you pull the focus ring down and the lens magically has a real manual override. I can't be absolutely sure if it is truly mechanical or just cleverly imitated (probably the latter), but it acts and is responsive like the real thing. Even better, you can use AF any way you like and when the right moment comes, pull the focus ring down to a preset position you decided on beforehand and it will focus back right where you want to be. Now that is an improvement over my 12-60. I love this. The only possible downside is the focus ring can be easy to activate by accident.
No 12-40 for you.
On the field, the 12-40 behaves like many recent m43 lens be it prime or zoom: fast, confident and silent. Limited only by whichever type of AF system your camera has and which generation your camera belongs to. It is a bit slower on a body like the classic E-PL1, but my GM1 and my trusty EM5 are on fire with the PRO lens attached. So already here, purchasing this lens is halfway justified by this point: It has fixed my AF problem.
One important detail is the old 12-60 was optically corrected; the 12-40 is software-corrected. For most people I guess the results matter more than how you get there. But I do use a RAW editor where I have to manually input the lens profile for every photo taken with the 12-40 otherwise the photos come out uncorrected. If you are shooting subjects with clear, straight lines then these distortions, uncorrected, can spoil your photos. But I find in non-critical work, uncorrected distortions are a non-issue and can even be a bit of cheat sometimes as they allow you to cram more in the shot in the wide end (it's like shooting at 10-11mm). So I often opt to leave my RAW photos as they are, choosing to correct only a handful, if any.
Well suited for pseudo macro and image stacking
On paper and with various technical reviews out there, the 12-40 beats the 12-60 with IQ. But in the real world, to me, the lenses are on par. This is not a bad thing. I love the IQ in the old lens: it's sharp, colorful and it has character. IMHO, either zooms match mid-level primes on m43 so I see little difference between them and, say, a Lumix 20mm f1.7 or a Zuiko 25mm f1.8 except for speed (aperture) and size. The more professional primes, like the Nocticron 42.5 f1.2 or the Zuiko 75mm f1.8, still have an edge in sharpness and "character". Ultimately, I think the 12-40 is only really limited by whatever your camera sensor is capturing and future improvements in sensor technologies will likely make 12-40 IQ even better.
Not just with the old 12-60 f2.8-4, but with the wide range of other competing zooms on m43, the usual trade-off between the different models is speed vs range. To me the 12-40 has the balance right, with enough speed and range. I take most of my photos below 40mm so that extra speed comes in handy in pure light-gathering abilities. If I need a bit more zoom, I would rather crop with the 12-40 than raise the ISO sensitivity or lower the shutter speed (which would be needed with a slower lens). This was a similar rationale for me with other highly competent zooms on m43 such as the Zuiko 12-100 F4 or the Panasonic 12-60 f2.8-4 and why I decided against them. I don't think constant f2.8 makes the 12-40 a low light lens per se, but I use it more often indoors than I ever used the old 12-60 or any of the much slower kit zooms I also own.
Yes, it can shoot landscapes too.
Speaking of which, the 14-150mm f/4-5.6 II that I own has a very practical focal range, very handy when travelling. It's also weather-sealed which is great. But it's noticeably a slower lens, which makes it more of a strictly outdoors lens (unless you use a flash). I think the IQ is ok, but noticeably below that of the 12-40. In this case, the 14-150 asks you to trade IQ and speed for focal range in comparison to the 12-40. Still a practical lens, but I never use it for anything critical. On the flipside, some kit zooms with narrower focal range like the Lumix 12-32 f/3.5-5-6, which I also own, offer some pretty sharp pictures in good light (and once you stop them down). There's no weather sealing with the 12-32, it's also slow and it doesn't have even a focus ring, but the lens is tiny, yet packs a lot of IQ at a fraction of the size and price (almost free when bought as a pack-in with a Panasonic camera body). If you anticipate shooting in broad daylight or in close proximity to subjects with a flash (like with a smartphone) then the 12-40 may seem overkill in those narrow circumstances compared to the 12-32. But of course, there are a variety of different shooting conditions so the 12-40 is much more flexible tool overall.
Though I can not speak from personal experience, the most obvious rival to the 12-40 is the Panasonic Lumix 12-35 f/2.8 (mark I and mark II). A similar, constant aperture zoom that is a bit smaller, a bit pricier, doesn't zoom as far and features the one feature missing from the 12-40: optical stabilisation. Since all Olympus m43 bodies and an increasing number of Panasonic bodies feature in-body stabilisation, I consider this 12-40 omission a non-issue. But recently, both Olympus and Panasonic have being pushing dual IS, both optical and in-body IS, for even greater stabilisation. Again, not much of an issue for me. But considering all the positive reviews the 12-35 lens has received, I'd likely be a satisfied customer if I owned it. Just be aware the Panasonic lens exist and should be considered if you are in the market for a constant aperture zoom.
Big performance usually equals bigger footprint.
And then comes the source of many arguments with m43: subject isolation. When compared to larger-sensored camera systems, m43 offers less DoF control when aperture is the same. In practice, you can get pretty good subject isolation on m43 with f2.8, but you have to work harder for it. For example, you can use the 12-40's pseudo macro abilities and get real close to your subject while keeping the background farther away. Bang! Easy bokeh. Conversely, you zoom all the way to 40mm, keep the lens at f2.8 and that gets you a decent half-body or head shot. Of course, if you use the same techniques with a f2.8 zoom on FF, your subject isolation would be more dramatic than on m43. it depends on how much is enough for you. Conversely, if you shoot more than a single subject, you'd likely have to stop down significantly on FF to get all your subjects in focus while on m43, maybe you'd stay at f2.8 or stop down significantly less which would help in a situation where light is not plentiful. In the end, only you know what you want and what you need. If subject isolation is a sticking point for you, then maybe faster primes are a better solution or just moving to a larger sensor camera system would be better for you in the end.
In conclusion, I find the 12-40 flexible enough for a whole range of shooting situations, has all-around good IQ with a good build and feel. It has replaced most of my primes in terms of general use and only my 8mm f/1.8 FE Pro competes with it for most time spent on my EM5 mark II camera. Highly recommended.
