Some articles on lens, double, double lens:
... Petzval's portrait objective lens (Petzval Porträtobjektiv) was an almost distortionless Anachromatischer vierlinser (double achromatic objective lens, with four lenses in three groups) ... The luminous intensity of this flat "portrait lens" was substantially higher than the daguerre standard of 1839, the Wollaston Chevalier lens (f/16) ... The portrait objective lens consisted of a cemented double lens in front (f/5) and a double lens with a gap in the back ...
Famous quotes containing the word double:
“Societys double behavioral standard for women and for men is, in fact, a more effective deterrent than economic discrimination because it is more insidious, less tangible. Economic disadvantages involve ascertainable amounts, but the very nature of societal value judgments makes them harder to define, their effects harder to relate.”
—Anne Tucker (b. 1945)