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At a 35mm-equivalent focal length of 600mm, Olympus delivers the first real pro-level supertelephoto lens for the Micro Four Thirds (MFT) mount with its M.Zuiko 300mm f4 IS Pro. Mirrorless MFT cameras have a smaller lens mount and tend to be substantially smaller than APS-C-based mirrorless and dSLR models, so this comparatively compact lens can significantly decrease the schlep factor for serious wildlife and sports photographers. Provided, that is, you're willing to sacrifice a little of the photo quality and resolution those larger-sensor cameras afford.

At $2,500, £2,200 or AU$3,500, the lens unsurprisingly bears a pro price tag as well. But if you need the distance or the its comparatively close focus and shoot with an MFT camera, especially one of Olympus' newer Sync IS-supporting cameras, it's worth it.

In those cameras, such as the OM-D E-M1 I tested it with, Sync IS combines two-axis optical and three-axis sensor-shift stabilization for a total of five axes, using a new IS control unit and gyros in the lens and body. Olympus claims 6 stops of stabilization in this configuration, and my testing bears that out. I was able to handhold as slow as 1/10 second, though I could only get consistently stable results at 1/13 second -- if you're steady-handed, you'll probably do even better. If you want to slip it onto your Panasonic, you should still get about 4 stops, though I didn't test that.

Olympus claims that this is the company's "highest resolving lens ever" with "very little edge distortion." I can't validate the former statement, but my photos bear out that it resolves extremely well through f16, with the expected slight sharpness drop-off by f22, and I saw practically no distortion, vignetting or aberration/fringing. It incorporates a new coating, Z Coating Nano, a layer of nanoparticles and air on the front of selected lens elements to reduce the amount of light that gets reflected off the elements' surface (coatings reduce flare and fringing).

Physically, it's sturdily constructed of metal, albeit with plastic rings, and dust-and-weather sealed, though only cold-proofed down to 14F (-10C). I took it for a test run during the East Coast blizzard of January 2016 and it operated without any issues. It has a pull-out lens hood that you can twist to lock into place, and it kept snow from blowing onto the lens.

In the middle of the lens barrel is the manual-focus ring, which you enable by pulling towards you, exposing the distance scale. The manual focus is just a hair looser than I like, though not bad. I do wish the manual-focus clutch action was a little tighter though; it pulls back with very little effort and with cold, gloved hands I found myself accidentally switching to manual focus.

The lens performed well in blizzard conditions.

On the barrel, easily reachable with your left hand is a stabilization switch that turns it on or off both on the lens and in the camera. The focus limiter switch has three positions, 1.4-4 meters, 1.4 meters to infinity and 4 meters to infinity; it's also not terribly easy to manipulate in the cold. I almost wish the physical switches had been swapped between the IS and focus limiter. The IS switch has a raised center, and is thus easier to feel than the flat, three-way limiter switch. There's also a programmable function button on the barrel, but you can't program it for some of the most important settings, such as choosing the IS mode (to switch from all-way to just vertical, for example) or to set a predefined focus distance to jump to. The telemacro focus when set to the limited range is quite responsive.

The traditional tripod collar releases via a thumbscrew, and Olympus provides a cover for that section if you remove it entirely. There are tick marks to line it up on the barrel, but it only clicks into place when rotating it to odd angles -- not at the precise horizontal and vertical positions, which would be more useful. It does have grooves in the sides to slide into an Arca Swiss head, though.

It uses Olympus' silent focusing technology, and the lens is pretty quiet. However, I did hear a slight whine, which is likely the optical IS. That might affect your needs for video.

I really like the lens, and it delivers on all the core requirements for its purpose. But you also should consider that it's not without potentially adequate competition. Panasonic recently announced a dust- and splashproof 100-400mm f4-6.3 with Panasonic's hybrid IS system, that company's version of Sync IS. While it's not as fast (it's likely a stop slower than the Olympus at 300mm), it does offer a zoom and it's a lot cheaper at $1,800, £1,750 or AU$2,000.