13. B. Light Recording Devices
The oldest light-gatherers are our eyes.
- method: photons temporarily alter chemicals in rods/cones in eyes
- okay: color sensitivity in visible
- bad: not permanent, subjective
Next came photographic plates.
- method: photons permanently alter chemicals on plates
- good: permanent
- okay: not uniform color sensitivity -- best with bluer light
- bad: can be overexposed
Finally, charge coupled devices (CCD's) were developed
- method: each photon knocks loose electrons, "coupling" photons to charges
- good: can store electronic signal forever
- good: computers can use pixels easily
- good: difficult to overexpose
- good: sensitive to redder light
- bad: not so sensitive to bluer light -- overcome?
- FYI: used now in digital cameras
Later this week or next, we'll have a guest speaker who installed and calibrated a CCD, and then took pictures with it.