The Megapixel Race - not over yet (2006 ... 2009 ... 2012).
Often one comes across the argument that the resolution of current dSLRs (2006) have passed the resolution that current lenses are capable of resolving, so there is no more reason to develop new cameras providing even higher megapixel counts.
Edit 2009: Recent dSLRs still follow the line well
Edit 2012: The 36 MP Nikon D800 is beginning to show signs of deminishing returns, but total system resultion is still improving
While the argument may begin to hold some merit for consumer grade lenses it can be shown not to be true if using a good quality lens. The graph below plots megapixels versus imager resolving power as reported by DPReview
Resolution calculated is based on numbers reported by DPReview as:
Resolution = vLPH x hLPH x pixelwidth / pixelheight
hLPH is horisontal lines per imager HEIGHT
vLPH is vertical lines per imager HEIGHT
pixelwidth and -height the dimensions of imager in pixels
hLPH x pixelwidth / pixelheight effectively corrsponds to lines per imager WIDTH
The resolution assumes to somewhat odd unit of square-lines or dots per imager surface, but that is what you get when you multiply lines by lines ;-)
Lenses like the Canon EF 50mm f/1.4 have been shown to resolve up to 90 line-pairs per mm - or 180 lines pr mm. On a 24x36mm imager this would correspond to about 28 megalines while on a 1.6x "cropping" imager it would correspond to about 11 megalines. It can be extrapolated from the above graph that imagers of 47 (full frame) and 18 (1.6x) megapixels would be required to capture all the data resolved by the Canon EF 50mm f/1.4. So, with the current lens resolution the imager resolution can still at least double before we enter into the realm of reduced return for that particular lens. And Canon makes even better lenses than that.
At the end of the day, it is all about total system resolution - that is, if reproducing an image at a given physical dimension, then having an imager outresolving a given lens still produces a more detailed image than having an imager not outresolving the same lens. For some additional reading visit here and here.
Kjeld Olesen, December 20th, 2006
Edited June 17th 2009 + November 14th 2012