As a practical example, an astigmation corrected scanning flat holographio concave grating (SFHCG) is designed and some results of the numerical and optical experiments are given.
While Galileo used a concave lens for his eyepiece, the standard refracting telescope uses a convex, converging lens for both the objective lens and the eyepiece.
They plunged into the concave field on the other side of which rose the village-the field wherein Jude had received a thrashing from the farmer many years earlier.
In the middle of the concave side, there is a groove twelve inches deep, in which the extremities of the axle are lodged, and turned round as there is occasion.