Within 10 years or so, we'll have HUGE cheap sensors (say $2000) while glass prices are remaining stable.
At some point the current trend to expensive high-resolving glass on 35mm cameras will reverse, and it'll be cheaper again to make low-resolving lenses stuck on large sensors.
Edmund
Edmund,
I think you might have a fascination with old MF and LF lenses which may now be bought for a bargain because they are obsolete. Lenses one owns, as a total for a particular format, generally tend to be the most expensive component of any camera system.
A relatively affordable, very large sensor with a big pixel pitch, say 12 or 18 microns, could certainly be used with old, cheap lenses to produce (potentially) impressive results, perhaps on a par with a P65+ used with a modern Digitar.
However, the question that springs to mind is why would anyone want to saddle himself with such heavy, cumbersome and inflexible equipment? Even though a DB may fit a number of different camera bodies, each with their own set of lenses, and can therefore be described as having a certain degree of flexibility, it seems to me that none of the camera bodies on which the DB may be attached at any one time is a flexible piece of equipment, compared with 35mm. The flexibility of the DB system resides in the existence of a truck load of equipment which you certainly wouldn't want to take with you on a flight to China, or any other place outside of the studio.
The other issue which contributes to the inflexibility of the very large sensor is its DoF limitations, which I'm surprised no-one's mentioned so far. If we go back to Michael's eye-opening comparison between the Canon G10 and the P45+ at A3+ print size, we see that the shallower DoF in the P45+ print gave the game away. The G10 was used at F3.5; the P45+ at F11. In order to equalize DoF, the P45+ should have been used at F22.
Comparing prints of equal DoF with the G10 at F3.5, the P65+ would need to be used at F24; a 6x7cm DB at F34, and a 4"x5" sensor at F60. It's true you don't need modern, sharp lenses at these F stops, but you're also unlikely to get impressively detailed and sharp results, so what's the point?
Another issue, which also relates to DoF, is the fact that system resolution is dependent upon both lens MFT and sensor pixel pitch. However poor the lens, one can always improve resolution using a sensor with a finer pixel pitch (more pixels) up to a point.
This fact is demonstrated at Photozone where they have tested the same model of lens with both the 8mp Canon 20D and the 15mp 50D. A lens which seems mediocre on the 20D suddenly appears quite impressive on the 50D.
My own tests have demonstrated that a 15mp 50D at F11 has about the same resolution at the plane of focus as a 10mp 40D at F8, using the same lens. However, the DoF of the 50D image is noticeably greater.
The only advantage of the ultra-large, big-pixel sensor you propose, outside of the opportunity to 'mop up' a truck load of obsolete, low resolution lenses, is the dynamic range potential which the larger sensor always has. However, a potential is just that, a 'potential'. Reality depends on a whole lot of other technological innovation. Witness the superior DR of the D3X compared with the P65+.
