If the loaded rod is elastic its lower end may be fixed in a stand, and the spherically curved base w is no longer required.
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.
Since glass does not transmit the ultra-violet light, quartz is used, but such lenses can only be spherically corrected and not chromatically.
- The lens is spherically corrected for 00', but the sinecondition is not fulfilled.
According to Abbe, a system can only be regarded as aplanatic if it is spherically corrected for not only one axial point, but when it also fulfils the sine-condition and thus magnifies equally in all zones a surface-element situated vertically on the axis at this point.