No, It Ain't So

(duplicate post with, with some slight changes for the gearophile audience)

More than one Web site and a whole bunch of forum posts are now claiming that Fujifilm/Panasonic's just-previewed organic sensor is twice as good as the D800 sensor. The basis of that claim is to take measured DxO numbers for dynamic range that are post efficiency, post shot noise, post dark current noise, and post read noise and compare them with numbers that are theoretical engineering dynamic range pre shot. They also don't seem to understand that voltage-based dB works out to 6.02 to a photographic stop, so their math is not only comparing apples with oranges, but the math itself is wrong. 

The theoretical number for the new organic sensor is 88dB. Sounds great, doesn't it? That would imply 14.6 stops of dynamic range. 

But I guess those other sites didn't look to see what other sensor companies report their theoretical dB numbers as. I'll give you one for comparison: the Aptina AR1011HS sensor, which is a 10mp 1" sensor that's mostly the same as the sensor used in the original Nikon 1 cameras (missing the AF component): 84dB, or 13.9+ stops. Don't believe me? Click here, look in the right column. 

I've used Aptina for a couple of reasons. First, they're one of the few sensor makers whose stated specifications are available to anyone on the Web (Sony keeps theirs mostly private these days). Second, I wanted a sensor that was in a camera that everyone could agree doesn't perform as well as the one in a Nikon D800.

The Aptina measures on DxOMark at 11 stops dynamic range. That's measuring well saturation down to a signal to noise ratio of 1:1 in the image data. You don't want to use SN 1:1 data: there's as much noise as signal, and most people would have a difficult time seeing the signal at all. As I note in my book on the Nikon 1 cameras, the practical dynamic range of this sensor is about 7 stops. So, for the same sensor we have:

  • Theoretical: 84dB (13.9+ stops)
  • DxO Measured: 11 stops (implies voltage based 66.2dB)
  • Practical Measured: 7 stops (implies voltage based 42.1dB)

So don't go putting your D800's on eBay because someone threw a faux stone at the ego you've got vested in your sensor. Your D800 still outperforms almost everything else on the market.

Footnote: many pro video cameras are marked with "Gain" settings: 3dB, 6dB, 12dB, etc. To change those into stops, divide by 6. So a 6dB gain factor is a one stop adjustment.

text and images © Thom Hogan 2015 -- all rights reserved
@bythom on twitter, hashtags #bythom, #gearophile