Search results
Results from the WOW.Com Content Network
Values of range from below 25 for very dense flint glasses, around 34 for polycarbonate plastics, up to 65 for common crown glasses, and 75 to 85 for some fluorite and phosphate crown glasses. Most of the human eye's wavelength sensitivity curve, shown here, is bracketed by the Abbe number reference wavelengths of 486.1 nm (blue) and 656.3 nm (red)
Memorial in Jena, Germany to Ernst Karl Abbe, who approximated the diffraction limit of a microscope as = , where d is the resolvable feature size, λ is the wavelength of light, n is the index of refraction of the medium being imaged in, and θ (depicted as α in the inscription) is the half-angle subtended by the optical objective lens (representing the numerical aperture).
One must bear in mind that the human eye itself has an Abbe number V d ≈ 50.2 so the expensive, high-end optical glass types mentioned above have little value for central vision; however, the wearer's view through the side of a glass lens is not comparable to central vision through the eye: Low dispersion glass definitely makes optically ...
In all earlier kinds of glass, however, the dispersive power increased with the refractive index; that is, decreased as increased; but some of the Jena glasses by E. Abbe and O. Schott were crown glasses of high refractive index, and achromatic systems from such crown glasses, with flint glasses of lower refractive index, are called the new ...
When the imaging system obeys the Abbe sine condition, the ratio of the sines of these angles equal the (lateral absolute) magnification of the system. In optics , the Abbe sine condition is a condition that must be fulfilled by a lens or other optical system in order for it to produce sharp images of off-axis as well as on-axis objects.
Abbe condensers are difficult to use for magnifications of above 400X, as the aplanatic cone is only representative of a numerical aperture (NA) of 0.6. This condenser is composed of two lenses, a plano-convex lens somewhat larger than a hemisphere and a large bi-convex lens serving as a collecting lens to the first.
In contrast to most other eye glasses, shooting glasses usually only have one lens that corrects the ametropia of the dominant eye, which is used for aiming.This lens is selected in such a way that the maximum visual acuity lies on the font sight line element near the muzzle of the (non-magnifying) open type or diopter and globe type match sight line elements to get three points positioned in ...
Add 90° to axis value, and if the new axis value exceeds 180°, subtract 180° from the result; For example, a lens with a vertical power of −3.75 and a horizontal power of −2.25 could be specified as either −2.25 −1.50 × 180 or −3.75 +1.50 × 090.