Studio Tests - Lumix G 14-45mm F3.5-5.6 OIS lens
The GF1 is available in kits with two lenses - the compact Lumix G 14-45mm F3.5-5.6 zoom with optical image stabilization (OIS) that first appeared with the DMC-G1, and the petite but fast 20mm F1.7 'pancake'. We've already reviewed the 20mm pancake (link), so on this page we'll look at the 14-45mm zoom.
The Lumix 14-45mm F3.5-5.6 OIS does extremely well in our studio tests. Panasonic has integrated software correction of distortion and lateral chromatic aberration into the system design, and this pays off with near-perfect results for these aspects of our tests; the lens is also unusually sharp for its class. Compared to the Micro Four Thirds Olympus M. Zuiko Digital 14-42mm F3.5-5.6 ED, the Panasonic does better in almost every regard; it even out-performs the best of the kit zooms for conventional DSLRs, the Olympus Zuiko Digital F3.5-5.6 ED. The differences aren't necessarily huge, but they're there.
|Sharpness||Central sharpness is very high at all focal lengths. At wider settings the corners are noticeably softer, but at telephoto sharpness is very even across the frame. Optimal apertures are generally around F5.6 (as usual for the Four Thirds format), stop down further and diffraction gradually takes its toll, with F16-F22 best avoided unless extreme depth of filed is essential.|
|Chromatic Aberration||Lateral chromatic aberration is being corrected in software, and is therefore essentially nonexistent.|
|Falloff||We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the center. There's a little bit of falloff wide open at 14mm, but that's all.|
|Distortion||Geometric distortion is being corrected in software, and unlike the equivalent Olympus lens, almost completely so. Distortion is below 1% at all focal lengths, meaning that in practical terms you'll never see it.|
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. For most users this is completely transparent - the camera corrects both the viewfinder image 'on the fly', and the JPEG files it records. Also, both the SilkyPix software supplied with G-series cameras and industry-standard alternatives such as Adobe Camera Raw convert raw files correctly too (the relevant correction parameters are encoded directly in the raw file, and applied equally by programs which support the format properly). 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, mainly when shooting at wideangle, along with color fringing due to lateral chromatic aberration.
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 the telephoto end. It's fair to say that wideangle images would require correction in most cases - not only to render straight lines correctly, but also to match the original viewfinder composition.
To place this in a wider context, the graphs below shows the distortion behavior, both corrected and uncorrected, compared to Olympus's two 14-42mm F3.5-5.6 ED kit zooms, first the 'regular' Four Thirds lens and second the collapsible Micro Four Thirds lens sold with the E-P1.
|Compared to Four Thirds
Olympus ZD 14-42mm F3.5-5.6 ED
|Compared to Micro Four Thirds
Olympus M ZD 14-42mm F3.5-5.6 ED
The first graph shows that while the the lens's uncorrected distortion is indeed high, the results when the files are properly processed and corrected are very good indeed. The sub-1% values indicate visually insignificant distortion through the entire range (in contrast to the visible barrel distortion that SLR kit zooms such as the ZD 14-42mm tend to show at the wide end).
The second comparison reveals the different approaches Olympus and Panasonic have taken towards lens design and distortion correction in their respective Micro Four Thirds kit lenses. The uncorrected images show near-identical barrel distortion at wideangle, but the Olympus design gives strong pincushion distortion at telephoto, in contrast to the Panasonic's neutrality. Also while Panasonic corrects distortion almost completely in software, Olympus is slightly under-correcting (so that the final results from its Micro Four Thirds lens are almost identical to those from the 'regular' Four Thirds version).
Lateral chromatic aberration
The studio test data also clearly shows that lateral chromatic aberration is being corrected in the ACR-converted raw files (out-of-camera JPEGs are the same). The practical upshot of this is that the camera produces images which are essentially free of the color fringing which is normally visible with this type of lens, most obviously towards the corners of the frame. Note that this isn't anything new with JPEGs - Panasonic's compact cameras and Four Thirds DSLRs have clearly been doing it for a few years - but it's unusual to see it applied in a mandatory fashion to third party raw conversions.
Again we've used dcraw to process our studio test raw shots in order to reveal the lens's true characteristics, and illustrated the fringing visually using the top left checkerboard pattern from our lens test chart. Note that, for the sake of clarity, where necessary we're using images corrected for barrel distortion in this comparison (using Adobe Photoshop's 'Lens Correction' filter with parameters of +7.5 at 14mm, +5.4 at 18mm and +2.8 at 25mm).
The 14-45mm shows moderate levels of chromatic aberration in this test, no worse than typical DSLR kit lenses and indeed overall better than the Olympus M ZD 14-42mm. The relatively linear shape of the CA profiles also helps explain the effectiveness of the software-based correction. Unusually the most visible CA isn't at the widest setting but towards the middle of the range (18mm and 25mm), due to the strong red component at these focal lengths.
One curiosity is that, while Panasonic is correcting lateral chromatic aberration in software, Olympus doesn't seem to be following suit. This means that if anyone does choose to use this lens on an Olympus E-P1, they will see this fringing in their shots.
Change in angle of view on focusing
One feature of the 14-45mm is that its angle of view gets distinctly wider on focusing closer. This sort of thing happens to some extent with most kit zooms, but in this case the effect is much more marked than usual, which is likely due to the internal focus design. The net result is that at relatively near subject distances (~2m or closer) that 45mm telephoto end actually gives a slightly wider angle of view than the Olympus M ZD 14-42mm at 42mm (although at long distances the situation is of course reversed). This has little impact in practical use - you just need to move a bit closer with the Panasonic than you would with the Olympus to get the same framing - but it's worth noting.