Early plates were sensitive to blue-to-UV light. These wavelenths of light come to a different point of focus than the greenish wavelengths the eye is most sensitive to. So there was a visual focus and a chemical - sometimes called actinic - focus with the early non-achromatic lenses.
Originally Posted by RalphLambrecht
In diminishing wavelength (or increasing frequency) the colors of light are (infrared)red-orange-yellow-green-blue-indigo-violet(ultraviolet).
Last edited by E. von Hoegh; 09-25-2012 at 10:59 AM. Click to view previous post history.