Dynamic Range -- what it is, what it's good for, and how much you 'need'

Started Oct 17, 2011 | Discussions thread
Great Bustard
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In reply to FrankyM, Oct 18, 2011

FrankyM wrote:

If you understood what DR was, then you'd not be confused on this point. Would you like me to explain to you how it works out? Specifically, why neither sensor size nor pixel size figures into the calculation of DR?

Maybe you should explain it to Chuck Westfall, Technical Advisor in Canon USA's Pro Engineering and Solutions Division. who says

http://www.dpreview.com/articles/5149972341/canon-eos-1d-x-overview

'There's a couple of things that we consider when we think about IQ: number one on this sensor is noise. It's clear the noise level is better than in the 1D Mk IV or the 1DS III. The pixel size is larger than in the 1DS III or 5D Mark II (6.95 microns, versus 6.4) and the difference is even more striking compared to the 5.7 micron pixels in the 1D Mark IV. That helps us in terms of light capturing ability and increases the signal to noise ratio. In turn, that does nothing but help the dynamic range of the camera. '

It's easy to see that pixel size is not the player, but rather sensor size and efficiency. The pixels in the 5Dc sensor have 58% more area than the pixels in the 5D2 sensor, yet the 5D2 has less noise and more DR. Why? Quite simple -- the sensors are the same size, but the 5D2 sensor is more efficient.

So, the sensor in the 1Dx will have less noise and more DR due to a more efficient sensor, which, of course, one would expect after four years since the 1Ds3 (when the 1Dx is released).

In short, the larger sensor results in less noise by collecting more light for a given exposure than a smaller sensor with the same efficiency, but has no effect on the DR, nor does the size of the pixel. Instead, the DR is a function of the sensor efficiency (bold emphasis mine):

http://www.dpreview.com/news/1110/11101810canoneos1dx.asp

The new 18-megapixel full-frame CMOS sensor utilizes large pixels – 1.25 microns larger than those in the EOS-1D Mark IV sensor and .55 microns larger than those in the EOS 5D Mark II sensor – together with gapless microlenses to achieve enhanced light gathering efficiency, higher sensitivity and less noise at the pixel level. The new sensor has improved on the already very high signal-to-noise ratio of sensor output of earlier EOS models for outstanding image quality, even in extremely low light.

Of course, larger pixels do help with "less noise at the pixel level", but, as a photographer, I'm considerably more interested in less noise at the image level, and, for a given sensor size and efficiency, more pixels result in less noise, not more:

http://forums.dpreview.com/forums/read.asp?forum=1032&message=39544926

In other words, if Canon could have made a 36 MP sensor that was just as efficient as the 18 MP sensor, noise performance, at the image level , would be superior to the 18 MP sensor.

The question, of course, is why they couldn't make a 36 MP sensor just as efficient. The answer is likely not that they couldn't, but that they chose not to due operational considerations. That is, a 36 MP sensor may not have been able to keep the same frame rate as an 18 MP sensor (there is evidence that is why the D3 and D3s did not have more pixels as well).

So, combine that with a marketing spin based on so few understanding the difference between a pixel level measure and an image level measure, and, voila, the 18 MP FF sensor in the 1Dx being sold as having less noise in part due to larger pixels to cover the fact that Canon couldn't get the desired frame rate with more pixels.

But, for sure, the greater sensor efficiency most certainly helps with both better noise performance and greater DR.

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