Nikon D90 or Pentax k20d or Cannon 50d

[Sushigaijin]

well, my point wasn't intended to be "olympus makes the best lenses," because there are a LOT of good lenses out there. I'm just concerned that FF format is butting up against a wall that is old lens technology. Certainly other manufacturers have digital-specific lenses that are very good - but that method of lens design needs to be integrated into the market where legacy lenses rule - full frame. Digital specific full-frame lenses, and super high resolution lenses, need to be designed to cope with the incredible rendering ability of FF sensors.

[Dougjgreen]

well, my point wasn't intended to be "olympus makes the best lenses," because there are a LOT of good lenses out there. I'm just concerned that FF format is butting up against a wall that is old lens technology. Certainly other manufacturers have digital-specific lenses that are very good - but that method of lens design needs to be integrated into the market where legacy lenses rule - full frame. Digital specific full-frame lenses, and super high resolution lenses, need to be designed to cope with the incredible rendering ability of FF sensors.

Frankly, 4/3 is probably closer to butting up against the limits of the lenses than Full Frame is, because the pixel density of a 12 MP 4/3 sensor is twice that of a 21 MP Full Frame Sensor. For a given resolution - say 12 MP, the pixel density of 4/3 is ~50% greater than APS, and around 3.5 times the density of Full Frame. And having used many legacy lenses on 4/3, I can state that only very good legacy lenses can really resolve the pixel density of a 10 MP 4/3 sensor - and only the VERY best legacy lenses can do it wide open, most need to be stopped down 1-2 f-stops to outresolve a 10 MP 4/3 sensor. This is why Olympus needed to really design many of their lenses from scratch for their new format. When they introduced the format, with a 5 MP sensor, it wasn't that much of an issue, but they certainly knew that at resolutions of 10 MP and above on that small sensor, they were going to need better lenses than what was out there.

The other issue, is angle of incidence in the corners of the frame. This is the one area that the 4/3 sensor has an advantage, compared to full frame. Most legacy lenses are quite a bit weaker in the corners of a full frame than they are in the center - in addition, there are diffraction effects and caused by the glass cover that is atop the sensor pixels, and thickness effects of the pixels themselves - because they use multiple metal layers of the semiconductor. These effects serve to scatter the light that hits the corners on an angle, across adjacent pixels. In general, this is not a major problem with telephoto lenses, but it is a problem with wide angles - and why modern wide angles designed for the digital format they are used for, are much better than legacy wide angles.

But APS has very nearly as much of an advantage as 4/3 compared to full frame as far as angle of incidence is concerned, and noticeably less disadvantage with respect to pixel density.

So, there are TWO factors involved in making lenses work with the newer digital sensors. Both high resolution and angle of incidence are issues. Physically smaller sensors have a worse issue with resolution, while bigger sensors have a worse issue with angle of incidence.