Consider what might be possible with a camera such as the 5D, which as you know has rather amazing low light capability at ISO 3200. 4 to 1 binning would give you a 3mp sensor with a huge dynamic range and superb low light capability at maybe ISO 6400.
Now that would be a very, very useful feature. Why is no manufacturer providing it?
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Ray,
that is a good question to end with, because I tend to believe that no-one is manufacturing such a camera even in high end professional video cameras for good practical and technical reasons, not due to the higher cost of 24x36mm sensors, or an industry-wide failure to appreciate the widely touted advantages of larger sensors and larger pixels.
What formats are judged by experts with very large budgets judge to be good choices for high end digital video? 2/3" and smaller. The current state-of-the-art seems to be Sony CineAlta 24P HDCAM cameras, $80,000 items using 2/3": 6.6x8.8mm in 4:3 mode, cropped to about 5x8.8mm for 16:9 format.
As to why, I can only speculate:
1) a camera's high shutter speed/low light performance is, as you should well now by now, limited by maximum aperture size, not directly by pixel or sensor size. Using larger sensors and pixels with the same aperture size if anything makes things worse: the same amount of light gathered and delivered to the sensor and so the same signal (in photons) is available at each photosite, but there will probably be a bit more read-noise.
2) HD video camera lenses can have very low aperture ratios. Many zoom lenses for 2/3" format HD cameras offer f/1.8 over a wide zoom range like the Fujinon HA22x7.8DERD-S 2/3" 22x High Definition Lens: f/1.8 at 7.8-122mm ("31-488mm equiv.") and reaching 172mm ("690mm equiv") at f/2.5. (Standard definition zoom lenses go even faster, like one offering f/1.4 at 9.5-253mm ("40-1000mm equiv.") Strangely primes seem not to get much faster, say f/1.5: maybe sensor/micro-lens characteristics limit minimum f-stop.
3) AS to dynamic range: at HD pixel counts like 1080x1920, pixel pitch on a 2/3" sensor is about 4.8 microns, and despite some wild exaggeration of DR needs in forums, this is large enough to give quite good dynamic range, way beyond what a straight print can display. For example, it is about the same pixel spacing as in the Kodak KAI-10100 4/3" interline CCD mentioned above and used in an astrophotography camera, and surely the astrophotography market cares about dynamic range.
So maybe speed limits are already set in 2/3" format largely by lens size and weight (or even desire for adequate DOF!), so that larger formats would by limited much of the time to similar aperture sizes, and thus not much opportunity for speed gain.
In this case, you can not argue that Sony is not capable of making sensors larger than 2/3" format.
Aside: Any suggestions as to why all high end video cameras, including those from Canon, use interline CCD's rather than CMOS sensors?
