Usually a zoom lens with a big coverage range goes hand in hand with a bunch of caveats and compromises. Olympus aims to change that notion with the M.Zuiko ED 12-100mm F4.0 IS PRO, a premium $1,300 lens that starts at a very wide angle and zooms to snap telephoto images. It's not optically perfect—there are some drawbacks when you shoot at 12mm—but it makes a lot fewer compromises than other lenses that cover a similar range. Micro Four Thirds owners shopping for a long zoom for travel and to minimize lens changes should take a really close look at the 12-100mm PRO, an Editors' Choice.

Design

The 12-100mm ($1,199.00 at Amazon) measures 4.6 by 3.1 inches (HD), weighs 1.2 pounds, and supports 72mm front filters. It's a big lens—it about doubles in height when zoomed to 100mm—so it's not a great fit if you own a small camera. I used the lens with one of the larger Micro Four Thirds bodies, the Olympus OM-D E-M1 Mark II, and found that it balanced quite well. I imagine it would also pair nicely with an E-M5 Mark II with its add-on grip, Panasonic GH5, or Panasonic GX8.

The barrel is finished in black metal with knurled focus and zoom rings. The focus ring sits at the front and operates as a clutch; pushing it forward sets the lens to autofocus and pulling it back toward you switches to manual. The zoom ring is larger, occupying almost all of the middle of the barrel, with 12, 18, 25, 35, 50, 70, and 100mm positions marked. A reversible lens hood is included, along with front and rear caps, and a soft drawstring pouch.

As with other clutch-focus Olympus lenses, manual focus is a very pleasant experience. The focus ring turns with some resistance, with hard stops at infinity and the minimum 5.9-inch focus distance. In between the two extremes is a printed distance scale, shown in both feet and meters. When zoomed all the way and focused to the minimum working distance you can magnify objects at 1:3 life-size. That means your subject will be projected onto the camera's image sensor at about one-third the size it is in reality.

Because it's a Micro Four Thirds lens, there's about a 2x crop factor to convert the field of view to that of a full-frame lens. If you're used to shooting on film or a full-frame system, the lens roughly matches the angle of view of a 24-200mm zoom—about the same as you get with one of the best all-in-one zoom cameras we've tested, the Sony RX10.

There are a couple of controls on the lens itself. One is the programmable L-Fn button; you can set its function via your camera menu. The other is an On/Off switch for the image stabilization system. Olympus states that when you pair this lens with the OM-D E-M1 Mark II ($300.00 at Amazon) , the combination of in-lens and in-body stabilization delivers 6.5 stops of correction; according to its marketing material, that's the best you can do as the rotation of the planet prevents further compensation.

It's a bold claim, but not far from the truth. From a seated position, I was able to shoot images at 1/3-second with absolutely no blur, a full six stops better than the 1/200-second that is expected to net sharp images when shooting at the maximum zoom. I was able to shoot images at one second with just a slight blur for most shots and quality in line with the 1/3-second shots when I took extreme care in controlling my breath, exhaling as the image was captured, and keeping the camera steady. Images shot at 1.6 seconds were noticeably blurry for the most part, but occasionally I got a decent result.

Standing on two legs puts more stress on a stabilization system. From a standing position I was able to snap consistently crisp images at 1/3-second. I was able to push the shutter speed further, to 1/1.6-second, and realize shots with very slight noticeable blur, but certainly good enough for sharing on the web and making modest-sized prints. Full one-second exposures netted occasionally decent results, but most of my test images showed noticeable blur.

Image Quality

I tested the 12-100mm along with the 20MP OM-D E-M1 Mark II, the latest high-resolution camera available from Olympus. Imatest shows that optical performance is weakest at 12mm, but there's still 2,462 lines per picture height on a center-weighted sharpness test, which is a very good score for a 20MP camera. The center notches excellent marks, topping 2,900 lines, with the mid parts hitting about the same as the average. It's the edges of the frame that disappoint, showing a noticeably soft 1,611-line score.

Stopping down to f/5.6 improves edge performance noticeably, bringing them all the way up to 2,487 lines. The average score increases a bit as well, hitting 2,763 lines. Image quality remains strong at f/8 (2,619 lines), but drops a bit at f/11 (2,437 lines), f/16 (1,827 lines), and f/22 (1,267 lines).

At 25mm the edges issues at f/4 have gone away. The lens notches 2,775 lines shot wide open, with a modest improvement at f/5.6 (2,786 lines), and the beginning of a downward trend at f/8 (2,627 lines). Stopping down further isn't advisable, as you lose resolution at f/11 (2,493 lines), f/16 (1,940 lines), and f/22 (1,326 lines). Scores are just about the same at 50mm.

There's a very slight drop in resolution at 100mm. You get 2,640 lines at f/4, and 2,543 lines at f/5.6. Photos shot at f/8 show a significant drop to 2,240 lines, and it gets weaker from there—1,927 lines at f/11, 1,781 lines at f/16, and 1,301 lines at f/22.

Long zoom designs often show quite a bit of distortion. The 12-100mm lives up to that expectation at 12mm, where it exhibits about 3.1 percent of the barrel variety. This gives the images a slightly bulbous look, with straight lines curved outward, which is exacerbated when focusing close to a subject. At the longer focal lengths we tested—25, 50, and 100mm—distortion isn't visible in field conditions.

Another optical drawback at 12mm is corner illumination. Typically you want the edges and corners of your image to be as bright as the center. There's a noticeable dimness at the corners when shooting at 12mm f/4, about -1.5EV. Stopping down to f/5.6 cuts that to about -1EV, and at narrow apertures the deficit is negligible. That's also the case at f/4 through most of the rest of the zoom range, though we do see a -1.1EV drop at 100mm f/4, which is just outside of our -1EV tolerance. At 100mm f/5.6 and narrower the frame is illuminated evenly.

Conclusions

The Olympus M.Zuiko ED 12-100mm F4.0 IS PRO is one of the best long zoom lenses we've tested, offering a constant aperture design, close focus, and sharp imaging, with just a few optical issues at its widest angle and aperture. It also has very strong image stabilization, delivering six stops of compensation in our tests with the E-M1 Mark II. The relatively small Micro Four Thirds image sensor has a lot to do with it—we wouldn't expect to see a full-frame 24-200mm f/4 lens of this quality at anywhere near the price point or size of the M.Zuiko. If you're in the market for a travel or all-in-one zoom for your Olympus or Panasonic mirrorless camera, and don't mind spending some money, the 12-100mm is an excellent performer, and our Editors' Choice.

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