A punctiform object viewed through a spherical lens appears as a line.
If one looks through a lens obliquely to its optical axis, it will act as a prism (Fig. 16.22a). A prism refracts a light ray toward its base (Fig. 16.22b). In addition to this, the light is split into its component spectral colors. Light with a short wavelength (blue) is refracted more than light with a long wavelength (red). Astigmatic aberration is an undesired side effect that is present whenever one looks through a lens at an oblique angle.
This phenomenon should be distinguished from astigmatic or toric lenses, which correct for astigmatism of the eye when the patients looks through them along the optical axis.
Was this article helpful?