Look on the forums (fora?), and you'll see an awful lot of argument about image noise, dynamic range and the like, but perhaps rather less about lens quality - esp when pushed to the limits. Modern lenses are designed to cope well with the majority of ordinary applications, but how does the lens in the X10 fare when it's pushed a little? Mike Johnson wrote a great article on how to stress a lens some time back (long enough ago that it mentions film cameras....), which can still be found on his The Online Photographer blog.
I recommend it. In fact, the blog is required regular reading, full stop.
From that article, he explains some of the ways to push a lens to its limits, including some that I'll be trying with the X10:
- Test for flare. For example, shoot with a bright light source in the frame, especially off-axis, to uncover ghosting artifacts. Also try placing the sun or source of light outside the picture area, but let it shine on the object to show how susceptible the lens is to glare and give clues as to whether internal reflections in the lens are a potential problem.
- Move away from the optimum aperture to see whether performance drops off rapidly, or is more consistent across the range. Also see how performance varies from centre to edge.
- Check for performance across the focal distances. Noticed how many consumer tele zooms tend to be pretty sharp at longer lengths with closer subjects, but lose the plot the closer they get to infinity? Lenses don't necessarily have consistent sharpness from nearest to furthest distance.
- Stress the bokeh performance by shooting where bokeh is generally worse. This means wider apertures and closer focus distances with high-contrast imaged objects on both sides of the plane of best focus and as far as possible from it.
- Check for purple fringing (something that some earlier Fuji's have been rather prone to).
- Check for distortions - generally more obvious at wide angles with typical "barrel" distortion. It'll be interesting to compare some RAW and JPEG images here too, as many cameras nowadays make distortion corrections in the box so that they're making up for some of the compromises in the lens design. The questions is, does that really matter as long as the end results come out well? It doesn't bother me, but there are plenty of others who would much prefer to know that their lens doesn't require any kind of in-camera software trickery to turn out a decent image.