Following the Test Report in the October issue of the Sky and Telescope, Simon Kidd of Welwyn in the United Kingdom has written to us (and to the magazine) pointing out an error in the article.

Simon Kidd writes:

The Dynamics of Dynamic Range

I enjoyed Sean Walker's review of The Imaging Source DMK 21AF04.AS camera (October issue, page 36). But near the end he implied that a camera's dynamic range - its ability to record detail in faint and bright areas of a scene at the same time - is determined by the number of bits used in digitally sampling the image.

Not so!

The number of bits (often 8 or 12) determines only the resolution of the sampling, that is, the number of gray levels between pitch black and pure white.

Dynamic range is determined principally by the well depth and readout noise of the camera's pixels, both measured in numbers of electrons.

This misconception reminds me of the Spinal Tap guitarist who thought his amplifiers were of superior power because the controls went up to 11 rather than the usual 10!

Our thanks go out to Simon for taking the time to point this out.