"Full Frame" sensors

Kodak Pro SLR/n

There was an assumption from many people that when the first somewhat mis-named "full-frame" or 35mm size sensors appeared that it signalled the end for the smaller APS-C format. This certainly hasn't happened and far from being the dominant format the 35mm sized sensor has been restricted to fairly expensive high-end cameras. The Canon 5DMkII and the two Sony models are the cheapest currently, but still cost more than their APS-C equivalents. 

canon eos 5D Mk II
Canon 5DMkII

The cameras so far released are:-

I've used quite a number of these, the ones in bold, and two of my four current cameras use this larger sensor. The Leica M9 and Sony a850. 

leica M9 75mm voigtlander f2.5 heliar
Leica M9

Sony a850 28-75 f/2.8 SAM lens
Sony a850

So why hasn't the 35mm sized sensor become the standard? It should provide better quality, being larger and for the most part having less pixel density. It also gives an opportunity for the use of super wide-angle lenses. 

Price is obviously a factor, and companies have invested heavily in their APS-C and 4/3 lens ranges, so these smaller formats aren't going to disappear, but I would have assumed by now that we would see more cameras with the larger format sensor than we have. If they had proved more popular by now perhaps we would have seen more "budget orientated" models. Its always surprised me that no-one ever tried this anyway. Currently even with discounts the cheapest you can buy a 35mm sized sensor camera for in the UK is around the £1600 mark, for a body only. If you're moving up from a smaller format, then lens costs have to be added in to this. 

I don't really have an answer as to why this has become a somewhat marginalised format. Certainly there have been great advances in APS-C and 4/3 technology but the ultimate non-MF image quality and indeed the best high ISO performance still comes from the "full-frame" models. They are usually larger and heavier, but the Canon 7D is a brute of a camera and still sells very well indeed. Maybe it is price that is the ultimate factor in determining how many cameras get sold, and maybe there are good reasons why manufacturers aren't able to offer the larger format at a smaller price. Whatever the reason, the sensor revolution that the Canon 5D seemed to indicate, hasn't happened.