Dynamic range D800 FX vs DX - round two :)

Started Aug 21, 2013 | Discussions thread
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Grevture Veteran Member • Posts: 4,187
Dynamic range D800 FX vs DX - round two :)

The issue of DR and sensor area seem to never really settle down ...

There was a recent threadthat just hit its posting limit, so here we go for round two ...

Signature ron_9 asked:

Now I really don't know what dynamic range is a product of, but does that really change when you move between DX and FX on the d800.

The answer is yes.

Signature jfriend00 got it right in the very first response to ron_9:

An FX sensor doesn't have any magical property over a DX sensor that gives it more DR or lower noise. It's just larger and thus collects more light which gives it lower noise and thus more DR. There are other things that affect DR too, but I'm just describing the effect of noise on DR in this post. So, a DX crop on a D800 has less DR than a full sensor shot.

And Allen Olesen wrote - in the last post of the thread - a explanation as good as any:

We know that the same total amount of light to the sensor will create the same amount of noise in the final photo when viewed at the same magnification of the full photo. (Of course using same sensor technology). When compared to an FF camera, a 1.5x crop camera will need 2.25x higher exposure to show the same amount of noise, and those 2.25x higher exposure will result in the same total amount of light since the FF sensor has 2.25x more area.

We also know that a sensor of 2.25x area can take 2.25x more light before it clips the highlights.

This clearly shows that the difference between the exposure which will create a given, acceptable amount of noise, and the exposure which will clip the sensor, will increase when you increase the sensor size. And that is the same as saying that DR has increased.

So what is all the discussion about then?

Well, it seems a a lot of people get confused when you mix in cropping into this. But it is actually pretty simple. DR and noise in a final image is affected by the sensor area used for that image. The size of the entire sensor is only important if you actually use the entire sensor to capture the final image. It is whatever area of a sensor that is used for any given image which matter for DR and noise.

So if you shoot one image using the entire area of a D800 sensor, and then shoot the same image (same content, same light), but only using the DX portion of the sensor, then that second image will actually have less DR then the first. They both came from the same sensor, but they did not come from the same area of that sensor.

Again: It all boils down to the sensor area used to produce the final image. This is why using a D800 in DX crop mode will produce very similar results in terms of DR and noise as shooting the same images with a D7000. The D800 and D7000 use very similar sensor technology and the area used (DX crop of D800 vs entire aps-c of D7000) to create the image is roughly the same.

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