Response Curve of Canon EOS-D60 digital camera
by John Beale, Feb. 7 2003

D60 Transfer Curve

This graph shows the camera's response in pixel value (intensity measured from 0 to 255) for a given target luminance as measured in EV with a Sekonic L-508 spotmeter. The images were taken with a fixed sensitivity of ISO 100, and a fixed aperture of f/4.0, with different shutter speeds from 1/30 sec to 1/125 sec. The camera appears to have a dynamic range in excess of 6 f-stops, but exactly how much depends on how you interpret the left end of the graph, which trails off smoothly towards the 0 pixel value at low illumination levels.  Small features will be increasingly obscured by random sensor noise as you move farther to the left on the EV scale. I believe the true curves are very smooth. The graphs of measured data show slope changes only due to the finite +/- 0.1 EV repeatability of measurements with the L508 spot meter.

Measurement note: The test target used here is an inkjet print of a sample file calibration target from having several uniform grey regions. The Sekonic L-508 turns out to have more infrared response than expected; perhaps it uses an unfiltered silicon photodiode as a detector. This is a problem since the target's black inkjet ink is not as optically dense in the IR as in the visible, so when using a halogen light, the meter response did not correspond well to the visible shades of grey. I side-stepped this issue by using only fluorescent light for illumination, which has almost no IR content. With a Philips 25 watt compact fluorescent as a light, the meter response matched well to the subjective brightness of the squares.


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