alan little’s weblog

more pictures of greycards

2nd May 2005 permanent link

Whilst spending an entertaining and educating morning measuring prints of greycards, I realise that this would also be a good time to measure the dynamic range of the D70’s sensor.

Which turns out to be about 6 stops: 3½ under, 2½ over.

The mid grey bar with the red stripe shows a grey card at a standard exposure. The bars to the left and right show under- and overexposure in 1 stop increments. We go white - highlights completely burned out – somewhere between +2 and +3 stops.

On the underexposure side there’s still a clear discernible difference between -3 and -4; there’s still a slight measurable difference between -4 and -6 but I can barely see it, and I‘m sure it’s nearly all noise by then anyway. I assume you could keep underexposing more or less indefinitely without getting to RGB 0,0,0 – difficult under normal conditions to prevent any light whatsoever from reaching the sensor – but beyond a certain point you’re just taking pictures of the sensor’s background noise.

Greater underexposure latitude is presumably why current imaging software, such as Photoshop’s Shadow/Highlight adjustment, can do such a remarkably good job of salvaging recognisable (if noisy) detail from what appear to be the deepest shadows; whereas white is white – once a pixel is reading off the scale that’s it, game over.

Coming soon: a return from camera/printer geekery to actual photographs somebody might actually want to look at. But (some level of) one is part of being able to produce the other.

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