The little Olympus pancake lens puts in a decent performance in our studio tests, generally well-matched to the current batch of 10Mp Four Thirds cameras and with overall image quality broadly similar to the 14-42mm kit lens. The 25mm has characteristics more typically seen in wideangle lenses, particularly moderate barrel distortion and quite pronounced chromatic aberration, reflecting the necessity for Olympus to use a retrofocal design for this lens.
|Sharpness||The lens shows good (but not exceptional) sharpness across the frame even wide open, with little change on stopping down until diffraction starts degrading the image at apertures of F8 and smaller. As usual on Four Thirds, F16-F22 are best avoided unless extreme depth of field is critical.|
|Chromatic Aberration||Something of a weak point of this lens even compared to the 14-42mm kit zoom, chromatic aberration is quite high even close to the centre of the frame, and therefore visible across the much of the image. The somewhat unusual profile shows red/cyan fringing in the central region of the frame turning to green/magenta towards the corners; fringe widths also increase on stopping down, peaking at around F8.|
|Falloff||We consider falloff to start becoming a potential problem when the corner illumination falls to more than 1 stop below the centre. Falloff here measures one stop wide open, and disappears rapidly on stopping down - essentially little to worry about. The falloff pattern on the tested sample was slightly decentered with respect to the sensor.|
|Distortion||The 25mm shows modest barrel distortion (1.1%), with a little re-correction towards the corners; this could become an issue in some real-world shots.|
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. Overall the 25mm F2.8 is a competent performer, which handles most situations pretty well; in many ways it's the ideal 'snapshot' lens (and we mean that as a compliment).
One area where the 25mm F2.8 really excels is in its handling of flare. With the sun placed in the top corner of the frame, the lens resists flare very well, with patterning only becoming visible at apertures of F11 and smaller (which are not really ideal on Four Thirds anyway). Place the sun just outside the frame, and veiling flare is almost non-existent; a pretty impressive performance for a lens with such an exposed front element, helped no doubt by the simplicity of the optical design.
|1/250 sec F16, sun in corner of frame||1/2500sec F2.8, strong backlight|
Background blur ('bokeh')
One genuinely desirable, but difficult to measure aspect of a lens's performance is the ability to deliver smoothly blurred out-of-focus regions when trying to isolate a subject from the background, generally when using a long focal length and large aperture. Clearly here a 25mm F2.8 is unlikely to win any awards, and indeed it isn't the best lens in the world for obtaining blurred backgrounds. It does a pretty nice job with macro shots, giving smooth and complementary bokeh, however as the background distance increases, the bokeh tends to deteriorate. In the rose shot below, the rendition of the background is overall somewhat messy and distracting.
|1/320 sec F2.8, ISO 100||50% crop|
|1/2500 sec F2.8, ISO 100||50% crop|
Lateral chromatic aberration measured as rather high in our studio tests, and this is borne out in real world shots. Perhaps the biggest problem is that chromatic aberration becomes distinctly visible unusually close to the centre of the frame, and the shot below (whilst far from being an aesthetic triumph) illustrates this well. The 100% crops below are taken from the red-outlined points indicated on the thumbnail image; red/cyan fringing is clearly visible at the middle left and lower centre of the frame, turning to green/magenta fringing towards the corners. This presumably is the price to pay for such a compact retrofocal design.
|1/800s F5.6, ISO100||100% crop, mid left of frame|
|100% crop, lower left corner||100% crop, lower centre of frame|
Olympus ZUIKO DIGITAL 25mm 1:2.8 Pancake Lens