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Studio Tests

The M Zuiko Digital ED 9-18mmm F4-5.6, perhaps unsurprisingly, has broadly similar optical characteristics to its Four Thirds cousin, which is no bad thing. However there is some penalty for the compact design: the extreme corners are a little soft, especially at the wide end, and chromatic aberration is noticeably increased.

Compared to the highly-regarded Panasonic Lumix-G 7-14mm F4, the Olympus also holds up pretty well; in general it's at least as sharp in the center of the frame, but softer in the corners, and at 14mm it's sharper right across the frame. On Panasonic (but not Olympus) cameras the 7-14mm benefits from correction of lateral chromatic aberration; however when tested on the E-P2, it exhibits less objectionable fringing than the 9-18mm anyway. (Note measured sharpness is slightly higher on the G1 compared to E-P2, due to the lighter anti-aliasing filter.)

Sharpness
Central sharpness is generally very high, but the extreme corners are somewhat soft in comparison. Optimum results are generally obtained about a stop down from wide open - around F5.6 at 9mm, and F8 at 18mm. Diffraction starts to have a serious negative impact at F16, with F22 on the whole best avoided.
Chromatic Aberration
Chromatic aberration is distinctly high, with strong red/cyan fringing in the corners at all focal lengths, but particularly at the wide end. This doesn't change much with aperture, but if anything peaks at F8.
Falloff
We consider falloff to start becoming a potential problem when the corner illumination falls to more than 1 stop below the center. The 9-18mm shows no significant falloff at all.
Distortion
Distortion is being corrected in software, but even so is a little higher than the Four Thirds 9-18mm. At 9mm, barrel distortion measures 1.4% - potentially visible in real-world use - but this essentially disappears on zooming in to 14mm.

Macro Focus

We wouldn't expect wide angle zooms to be great for macro work, and the 9-18mm doesn't surprise. The measured minimum focus distance is 19 cm (in manual focus mode) - significantly closer than Olympus's advertised 25cm - giving a working distance of 9.5 cm from the front of the lens to the subject. Maximum magnification is likewise rather higher than Olympus's specification, at 0.16x.

Image quality is actually rather good - central sharpness is high and pretty even across the frame, especially when stopped down to F8 or F11. Distortion is extremely low, and there's just-visible red/cyan chromatic aberration.
Macro - 115 x 86 mm coverage
Distortion: Slight barrel
Corner softness: low
Focal length: 18mm (36 mm equiv)

Software correction of lens aberrations

A fundamental component of the Micro Four Thirds system design is the use of software to correct certain lens aberrations, most notably geometric distortion. For most users this is completely transparent - the camera corrects both the viewfinder image 'on the fly' and the JPEG files it records. Also, the relevant correction parameters are encoded directly in the raw file, which means that both the software supplied with the camera and industry-standard alternatives (including Adobe Camera Raw and Capture One) will convert raw files correctly. However users who like to experiment with more obscure raw developers which are unable to apply the requisite corrections will find themselves with highly distorted images, especially when shooting at the widest angles.

Geometric Distortion

The graphic below shows just how much distortion you can expect to see when working with an unsupported converter. There's severe barrel distortion at wideangle which reduces progressively on zooming in, with the lens giving almost perfectly neutral results at 18mm. Clearly images shot at the widest settings will require correction in almost all cases - not only to render straight lines correctly, but also to match the original viewfinder composition. However by 11mm distortion has fallen to levels commonly seen (and considered acceptable) from conventional SLR lenses, and between 14mm and 18mm it's almost nonexistent.

9mm (+ 4.7%) 11mm (+ 2.2%) 14mm (+0.5%) 18mm (-0.1%)

Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests.

Flare

Control of flare is a critical feature of a superwide lens; with such a broad view of the world, bright light sources will find themselves in the frame on a regular basis. Overall the 9-18mm does well in this regard, showing only occasional problems with flare, even without a hood. The only real problems occurred with a very bright light source towards the center of the frame, and with side lighting striking the front element at an oblique angle.

The samples below illustrate what you might be able to expect. With the sun in the corner of the frame at 9mm, the image is impressively clean, with contrast and detail well-retained. But with oblique side light we see multi-coloured flare streaks across much of the frame, which means it will probably be wise to invest in the optional lens hood when it becomes available.

9mm F8, sun in corner of frame 18mm F6.3, sidelight

Chromatic aberration

Wideangle zooms are bound to suffer from a degree of lateral chromatic aberration, but the M ZD 9-18mm F4-5.6 shows more than its fair share, with strong red/cyan fringing towards the corners of the frame at all focal lengths. In fact the fringe widths are some of the highest we've seen, and in unfavorable circumstances can be readily visible even at relatively modest image sizes. Unfortunately Olympus does not pass correction data to the camera (alongside the obligatory distortion correction), so the color fringing shows up with both Olympus and Panasonic camera bodies. However it can of course be suppressed when processing raw files.

The examples below show how this CA can appear in practice, using both Olympus and Panasonic bodies, and how well the fringing can be treated using Adobe Camera Raw's 'Lens Corrections' controls. This red/cyan CA isn't quite as unsightly as the green/magenta type, at least.

9mm, Olympus E-P2
12mm, Panasonic GF1
F5.6, camera JPEG F5.6, camera JPEG
100% crop, top left 100% crop, lower left
Red/cyan correction -33 in ACR 5.7 Red/cyan correction -30 in ACR 5.7

Corner softness wide open

Our studio test results indicate that the 9-18mm shows some softness in the corners of the frame when used wide open. In practice, this will rarely be much of a problem - the affected areas are really quite small, and it's relatively rare that fine detail in these regions is critical to the success of an image. On those occasions when there really is pictorially significant detail in the corners, you can normally just stop down a bit to sharpen it up anyway. The example below shows how this works in practice - at F4 the detail right at the top left corner is somewhat blurred, but stop down to F5.6 and it sharpens up quite nicely.

9mm, Olympus E-P2
1/2500 sec F4, ISO 200 100% crop, center of frame
100% crop, top left corner F5.6, 100% crop, top left corner

Background blur ('bokeh')

Wideangle zooms are never really the first choice for selective focus work but, if you shoot wide open at the lens's minimum focus distance, you'll get a degree of background blur. However it's not especially attractive, so you'll probably wish you hadn't.

18mm F5.6 50% crop
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