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Canon Unveils 120-Megapixel Camera Sensor
Barence writes "Canon claims to have developed a digital camera sensor with a staggering 120-megapixel resolution. The APS-H sensor — which is the same type that is used in Canon's professional EOS-1D cameras — boasts a ridiculous resolution of 13,280 x 9,184 pixels. The CMOS sensor is so densely packed with pixels that it can capture full HD video on just one-sixtieth of the total surface area. However, don't hold your breath waiting for this baby to arrive in a camera. Canon unveiled a 50-megapixel sensor in 2007, but that's not made it any further than the labs to date."
It's probably not going too far out on a limb to say that the any-day-now rumored announcement of an update to the 1D won't include this chip, but such insane resolution opens up a lot of amazing possibilities, from cropping to cheap telephoto to medium and large format substitution. Maybe I should stop fantasizing about owning a full-frame 1D or 5D and redirect my lust towards 120 megapixels.
A more substantial problem is that diffraction limits the effective resolution of an optical system to well above the size of each of these pixels. This is a problem with current sensors at narrow apertures; lenses exhibit a measurable loss of sharpness, typically f/11 and up, because the airy disks expand as the aperture contracts. With hugely dense sensors like this, though... plugging some numbers into a website that explains the whole situation suggests that you'd need to shoot with apertures than f/1.8 to get circles of confusion smaller than the size of a single pixel.
That's right--even "fast" f/2.8 lenses are limited by physics to never being able to project detail onto individual pixels. You could potentially add a deconvolution stage in software to recover additional sharpness, but not in hardware.
Another thing. Do the math: the pixels are 2.1 micrometers square. Compare to trichromatic human vision, which detects red light peaking at 564 nanometers, 0.564 micrometers. The size of a pixel is within a factor of four of the wavelengths they measure. Staggering.
Glass isn't the problem. We need new laws of nature, since we're near the edges of the ones we have now.
In principle, you get the exact same result or worse as with a cheaper sensor with less resolution where each pixel is simply 4 times larger and gets 4 times the light for the dark areas, and the bright parts will be maxed out anyway. And HDR usually means a much larger exposure difference than simply 4 times - say, 10 stop difference is a 2^10 ~= 1000 times more light for the dark parts.
It's not possible to get more range out of a single exposure, because the range is inherent in the capture based on how much light you choose to let in, and how sensitive your sensor is to that light. Dynamic range refers to the difference between the brightest and the darkest pixel the sensor can distinguish in that exposure. Beyond the bright end of the range, they all look the same white to the sensor. Beyond the dark end of the range, they also all look the same black.
Here's how HDR works, oversimplified. We take a shot where we meter the bright part, so that it'll be properly exposed, deliberately sacrificing the dark parts. All dark pixels will be black in this exposure because we didn't let in enough light for the sensor to make out the difference. We then take another shot where we meter the dark part, sacrificing any somewhat bright parts. All bright pixels will be white because we let in too much light for the sensor to make out the difference. If we then combine the two images by throwing away the dark parts of the bright shot and the bright parts of the dark shot, we get an composited image that has more range than either image alone, i.e., HDR. Note that no averaging is involved.
The alternate solution ceoyoyo is talking about requires a different kind of sensor. Imagine if you had two kinds of pixel sensors, one sensitive and the other insensitive. You'd alternate them on your sensor, perhaps in a checkerboard pattern, but basically pairing adjacent sensitive/insensitive pixels. Now, if your sensitive pixel registers too high a value, then it's probably blown out so use the value from the insensitive one (which is by definition not as bright). If the insensitive one registers too low a value, then it's probably too dark, so use the sensitive one (by definition not as dark). The crucial difference here is that you choose one over the other, and never average. If all you did was average, then the result is the same as using a single kind of pixel sensor with a sensitivity in the middle, and would not improve your dynamic range.