I'm just guessing -- but again, that's all anyone can do, since the full Four Thirds spec is proprietary.
Originally Posted by peterv
But based on the article I linked in a previous post, I'd say that:
-- Four Thirds lenses are designed to be "telecentric," i.e, designed so that rays from the lens strike the sensor at a fairly perpendicular angle. The angle at which rays strike the sensor is called the "chief ray angle."
-- The microlens array used in the Four Thirds sensor is optimized for the chief ray angle dictated by the lens spec.
-- Camera lenses that produce a significantly different chief ray angle will interact with the microlens array in a non-optimal way. Intuitively, I suspect that effects of this non-optimal interaction might include reduced sharpness, distortion, and color fringing.
Those are the sorts of effects you're seeing, right?
This is kind of a new world for everybody. Until Four Thirds, digital-camera systems with interchangeable lenses were designed to work with legacy lens systems from the film era. That meant that microlenses etc. had to be compromises.
The effects of these compromises were hard to isolate, and often tended to be blamed on the lens -- e.g. the digicam website "lens tests" that would say "lens X has chromatic aberration" because they'd see color fringing... even when lens X had never shown any sign of chromatic aberration in years of use on film cameras. (Color fringing and chromatic aberration are NOT one and the same thing -- chromatic aberration is actually a specific lens design fault of which color fringing is only one possible symptom.)
With Four Thirds, for the first time, we started seeing cameras, lenses, and sensors that had been designed without any concessions to the film-camera world. It wasn't a big deal because relatively few people were using legacy lenses on Four Thirds cameras. Now Micro Four Thirds comes along, with its thinner body depth that makes it possible to adapt all kinds of crazy lenses, and we have to expect to see more dramatic effects from lens-design philosophies that conflict with the assumptions under which Micro Four Thirds sensors were designed.
Cripes, that sounds pedantic! But it seems clear that "your mileage may vary" is going to be more true than ever as we experiment with various lenses on Micro Four Thirds.