Olympus E-P1 Review: 21. Lens tests: Digital Photography Review

Studio Tests - M. Zuiko Digital 14-42mm F3.5-5.6 ED lens

The EP-1 is available in kits with two lenses - the clever collapsible M. Zuiko Digital 14-42mm F3.5-5.6 ED zoom, and the slimline M. Zuiko Digital 17mm F2.8 'pancake'. For a start we're going to look at the zoom.

UPDATE 9/24/09: Lens test data has been updated using the full release version of Adobe Camera Raw 5.5 for image processing. The results are essentially the same as from the beta version we used for original publication, and the conclusions unchanged.

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NOTE the line marked 'Nyquist Frequency' indicates the maximum theoretical resolution of the camera body used for testing. Whenever the measured numbers exceed this value, this simply indicates that the lens out-resolves the sensor at this point - the calculated MTF values themselves become meaningless.

The M. Zuiko Digital 14-42mm F3.5-5.6 ED gives results which are a little pedestrian for an entry-level 'walkaround' kit zoom - it will certainly get the job done, just without any great degree of distinction. Clearly some compromises have been made to achieve the compact collapsing design; the 'regular' Four Thirds Zuiko Digital 14-42mm F3.5-5.6 kit lens performs better overall, with higher sharpness and rather lower chromatic aberration at wideangle, and much sharper results wide open at telephoto. Olympus is clearly correcting distortion in software, but (unlike Panasonic) leaving lateral chromatic aberration untouched.

Sharpness	Sharpness results are perfectly acceptable (if not outstanding), just not quite as consistent as the Four Thirds 14-42mm. The lens is a little soft at wideangle, especially towards the corners, and surprisingly only deteriorates on stopping down. It's also dramatically soft at 42mm F5.6, but in this case much better a stop down. At intermediate focal lengths sharpness is pretty good though, and consistent across the frame. Optimum results are generally obtained around F5.6 to F8.
Chromatic Aberration	Unlike Panasonic, Olympus is not correcting lateral chromatic aberration in software on Micro Four Thirds. Unfortunately CA gets a bit out of hand at wideangle, with highly pronounced red/cyan fringing in the corners of the frame at 14mm, setting a new record for kit lenses we've tested. Zoom in though and CA progressively decreases; from 25mm onwards it's almost disappeared.
Falloff	We consider falloff to become perceptible when the corner illumination falls to more than 1 stop less than the centre. There's simply nothing to see here - move along.
Distortion	Geometric distortion is being corrected in software, but curiously not completely - instead Olympus seems to have elected to match the characteristics of the Four Thirds 14-42mm almost exactly. Therefore we see mild barrel distortion at wideangle (1.8%), diminishing on zooming in; from 25mm to 42mm it's almost perfectly neutral. Not hugely objectionable by any means.

Macro Focus

Macro performance is actually rather good, as tends to be the case with front-cell focusing kit zoom designs. Our measured magnification is 0.31x, and this is is achieved at a focus distance of about 22cm (distinctly shorter than Olympus's specified 0.25m), giving a working distance of about 11 cm between the subject and the front of the lens.

Image quality is good too; much of the frame is soft at F5.6, but stop down to F8 or F11 and our test chart shot becomes sharp across the frame. There's very little CA, and distortion (being corrected in software) is essentially nonexistent.

Macro - 56 x 42 mm coverage
Distortion: essentially none
Corner softness: Low
Focal length: 42mm (84 mm equiv)

Software correction of lens aberrations

Geometric Distortion

A fundamental part of the Micro Four Thirds system is the use of software to correct lens distortions. For the majority of users this is absolutely nothing to worry about; the viewfinder image is corrected 'on the fly' when using the camera to take pictures, likewise JPEGs have the distortion removed too. However raw files are slightly different, and while both the supplied software (Olympus Master) and major third-party packages (notably those from Adobe) remove distortion too, if you wish to use a converter which doesn't properly support the system you may end up with distinctly bendy lines in your images. (Note that we'd expect most of the third party converters which don't currently offer distortion correction to rectify this sooner rather than later.)

The graphic below shows just how much distortion you can expect to see when working with an unsupported converter. The barrel distortion at wideangle is severe - correcting this would be essential in most images - but things aren't quite so bad at other focal lengths, and actually fall within the distortion range we see from conventional, rectilinear-corrected DSLR lenses.


14mm (+ 4.5%)	18mm (+ 2.1%)	25mm (-0.36%)	35mm (-1.64%)	42mm (-2.08%)

To place this in context, the graph below shows the distortion behavior, both corrected and uncorrected, compared to the Four Thirds Zuiko Digital 14-42mm F3.5-5.6 ED. Unlike Panasonic with its 14-140mm, Olympus is having to correct distortion at all focal lengths to match the conventional SLR lens.

Chromatic aberration

We've previously seen that Panasonic Micro Four Thirds bodies correct lateral chromatic aberration when used with Panasonic lenses, but the Olympus EP-1 does not. We were therefore curious to see what would happen if we used an Olympus lens on a Panasonic body (in this case the DMC-G1). The answer is that lateral chromatic aberration is not corrected, leading us to believe that the requisite information is simply not encoded in the Olympus lens's firmware.

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