Long exposures and dynamic range

<p>Just a curiosity, I don't know if this is the right forum... I know the dynamic range of a digital sensor decreases with higher ISO, but what about long exposures? Should I expect a lower dynamic range fro the camera?<br>

Thank you, Alberto.</p>

Are you referring to the DxO measurements? I wouldn't necessarily trust their ratings of dynamic range. Many cameras have wider dynamic range at ISO 200 than at 100, which disproves the theory. Some cameras (G12, S95) use a high-ISO trick for dynamic range optimization, and results are very respectable. EXR exposes half the photosites double or triple duration to increase shadow detail, while preserving highlight detail in the other half.

 

Long exposures increase noise, primarily. Your call on the relation between noise and dynamic range.

<p>Long exposures have increased noise due to thermal effects. Whether this has an effect on dynamic range depends on how you define the term.</p>

<p>DxO measures dynamic range based on the noise level to the saturation level. A better method is used by DPReview, based on the ability to resolve detail. The DxO method tends to favor cameras with better noise processing, and often fails to distinguish cameras with clearly better imaging characteristics, such as medium format digital.</p>

<p>Low noise does not necessarily mean useable image information. Conversely, image details can be seen even if there is substantial random noise. The noise level of my D3 is about the same as with my CFV-16 digital back, but the CFV can pull image details out of the murk to a much greater extent, and looks much more "open" in high contrast situations like landscapes in full sunlight.</p>

<p> </p><div></div>

<p>The example was taken in October, about an hour and a half after sunset. You could not see any details in the sky by eye, and I needed a flashlight to set the camera (or walk). The camera was an Hasselblad, CF40 and a CFV-16 digital back. The exposure was set with spot meter on the first balloon, just above the brightest part.</p>