In the “long” term (the next 2-3 years!), 30-40 megapixel DSLRs will emerge, a completely pointless development unless pixel quality improves substantially and optical performance rises to the challenge. Even today, the 21MP Canon EOS 1Ds Mark III demands exceptional optics to exploit the sensor, especially near the edges and in the corners. Worse, with those same exceptional optics, diffraction begins to degrade image contrast by f/8, so “wiggle room” is not great.
Resolution is certainly fun. This 21-megapixel image was taken with the Coastal Optics 60/4 APO macro on the Canon EOS 1Ds Mark III. Loads of detail. Could the Coastal Optics 60/4 deliver even more resolution at good contrast on a 36 megapixel sensor? It seems likely.
Canon EOS 1Ds Mark III + Coastal Optics 60/4 APO macro
At 36MP, an aperture no smaller than f/5.6 will be the limit at which image quality is reigned in by diffraction—which is not to say that perfectly wonderful images won’t be made down to f/11 or even f/16—it’s just that optimal contrast will be reached no later than f/5.6 with a top-grade lens on a 30+ megapixel camera.
So my belief is that as we move to the world of 30-40 megapixel full-frame DSLRs, only the world-class lenses will prove satisfying in the restricted f/2 - f/5.6 range. For that reason, it’s a strategic move to acquire world-class optics that might or might not be available in the future (and buying used at a steep discount is fine when care is taken). Already, alleged gems like the Cosina Voigtlander 125/2.4 APO can no longer be had. Who’s to say whether Leica will continue to make their 90/2, 180/2.8 and 280/4 APO models? Or that Coastal Optics will make their 60/4 APO macro for years on end? Such lenses are a long-term investment, not to be purchased on a whim, but not to be taken for granted, either.