## Astigmatism Sentence Examples

- The aberrations of the third order are: (1) aberration of the axis point; (2) aberration of points whose distance from the Aberra- axis is very small, less than of the third order - the tions of deviation from the sine condition and coma here fall together in one class; (3)
**astigmatism**; (4) curvature of the field; (5) distortion. - These anastigmatic lenses, which are manufactured up to X 40, are chromatically and spherically corrected, and for a middle diaphragm the errors of lateral pencils, distortion,
**astigmatism**and coma are eliminated. - The image is greatly affected with
**astigmatism**; but this is of little consequence, if y in (8) be small enough. - The correction of
**astigmatism**is in many cases a matter of considerable difficulty, but the results to vision almost always reward the trouble. - Airy, the astronomer, about 1827, corrected his own
**astigmatism**by means of a cylindrical lens. - If measures are made by placing the image of a star in the centre of the disk of a planet, the observer may have a tendency to do so systematically in error from some acquired habit or from natural
**astigmatism**of the eye. - (4) After eliminating the aberration on the axis, coma and
**astigmatism**, the relation for the flatness of the field in the third order is expressed by the " Petzval equation," I 1 = o, where is the radius of a refracting surface, n and n' the refractive indices of the neighbouring media, and / the sign of summation for all refracting surfaces. - The same holds for the errors depending upon the angle of the field of view, w:
**astigmatism**, curvature of field and distortion are eliminated for a definite value, w*; " zones of**astigmatism**, curvature of field and distortion " attend smaller values of w. - (2) Largest field of view; necessary corrections are - for
**astigmatism**, curvature of field and distortion; errors of the aperture only slightly regarded; examples - photographic widest angle objectives and oculars. - Photog., 1891, 5, p. 225; 18 93, 7, p. 221), cemented objectives of thin lenses permit the elimination of spherical aberration on the axis, if, as above, the collective lens has a smaller refractive index; on the other hand, they permit the elimination of
**astigmatism**and curvature of the field, if the collective lens has a greater refractive index (this follows from the Petzval equation; see L. - To eliminate distortion and
**astigmatism**when the centre of rotation of the eye coincided with the point where the principal rays crossed the axis. - In
**astigmatism**, owing to differences in the refractive power of the various meridians of the eye, great defect of sight, frequently accompanied by severe headache, occurs. - To), and does not influence the definition at the (primary) focus, although it may introduce
**astigmatism**.'