Search results
Results from the WOW.Com Content Network
In most cases, two thin lenses are combined, one of which has just so strong a positive aberration (under-correction, vide supra) as the other a negative; the first must be a positive lens and the second a negative lens; the powers, however: may differ, so that the desired effect of the lens is maintained. It is generally an advantage to secure ...
He concluded that the aberrations cannot be fixed with a combination of rotationally symmetrical lenses. [1] In his original paper, Scherzer summarized: "Chromatic and spherical aberration are unavoidable errors of the space charge-free electron lens. In principle, distortion (strain and twist) and (all types of) coma can be eliminated.
The idea of using the spherical aberration of a meniscus lens to correct the opposite aberration in a spherical objective dates back as far as W. F. Hamilton’s 1814 Hamiltonian telescope, in Colonel A. Mangin's 1876 Mangin mirror, and also appears in Ludwig Schupmann’s Schupmann medial telescope near the end of the 19th century.
In lens systems, aberrations can be minimized using combinations of convex and concave lenses, or by using aspheric lenses or aplanatic lenses. Lens systems with aberration correction are usually designed by numerical ray tracing. For simple designs, one can sometimes analytically calculate parameters that minimize spherical aberration.
Chromatic aberration of a single lens causes different wavelengths of light to have differing focal lengths. An apochromat, or apochromatic lens (apo), is a photographic or other lens that has better correction of chromatic and spherical aberration than the much more common achromat lenses.
The first is a third-order aberration, which occurs for objects (or parts of objects) away from the optical axis. This form of aberration occurs even when the optical system is perfectly symmetrical. This is often referred to as a "monochromatic aberration", because it occurs even for light of a single wavelength.
Spectacles and contact lenses correct "low-order aberrations", such as defocus and astigmatism, which tend to be stable in humans for long periods of time (months or years). While correction of these is sufficient for normal visual functioning, it is generally insufficient to achieve microscopic resolution.
Aspherics are only [citation needed] used for corrective lenses when, in order to achieve a flatter lens for cosmetic reasons, the lens design deviates from the best-form sphere; this results in degradation of the visual correction, degradation which can, in some part, be compensated for by an aspheric design. The same is true for atoric and bi ...