Originally posted by wll Today's APS-C sized sensors are getting better and better and in a few short years the sensor technology will probably change and make APS-C and FF and MF a moot point. [...]
I see what you are saying. And speaking for 2009, you are right.
However, in the mid term (where digital doesn't impose a size overhead at all) this isn't quite correct.
The K mount system is a full frame camera system (always has been) and there is no reason a digital K mount FF camera has to be any bigger than Pentax MX. Canon, Nikon, Sony only fail miserably to do it now but we all know that this is Pentax land anyway
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dedicated APS-C would have to be much smaller than any of the current FF mount / APS-C sensor bodies allow. A market niche. Probably to be filled by the Samsung NX, though ...
BTW, Olympus with their 0.5x sensor (which is about 110 film format!) has miserably failed to turn the massive size benefit into a significantly smaller camera system. The Pentax 110 SLR system was a case study what the FourThirds system ought to be. Chance missed...
One last word ... the technological progress in sensor technology won't last forever. We're approaching physical limits here. A reasonable (i.e., usable) 100 MPixel sensor most likely requires a FF sensor. And OLED photo walls will require the resolution ...
So, for now I agree to what you say. But it shall change in the future ...