Busch improved upon this with the pantoscope (fig. 14), and Dallmeyer introduced his wide-angle rectilinear (fig. I5)
Steinheil introduced what he called his periscopic lens (fig. 16), which consists of two uncorrected meniscus lenses of crown
FIG. 15. FIG. 16.
glass; and chromatic aberration not being eliminated, the focussing screen had to be brought nearer to the lens after focussing and before exposing, by 1/40 of the focal length of lens.
Mr. Sutton's panoramic lens (fig. 17) consisted of two concavo-convex lenses, with spherical curvatures and a hollow space
between filled with water. This possessed a wide angle, and gave no, or practically no, spherical or chromatic aberration, but from its peculiar construction, and the necessity of using curved plates, has never come into general use.
In figs. 18, 19, and 20 are shown some lenses by Steinheil, fig. 18 being an aplanatic rapid rectilinear, and figs. 19 and 20