Using a three dimensional formalism previously established, the freedom to choose the coupling functiong(&thgr;, &phgr;) between the polar angles defining the mean trajectory in the field‐free region of the analyzer is exploited to improve the properties of the instrument. It is shown that a partial correction to thezvariation of the image when &thgr; and &phgr; vary can be achieved yielding a maximum excursion &Dgr;z /zof 6% for a total &thgr; excursion of &Dgr;&thgr; = 18° at &phgr; = const with a corresponding increase of resolving power by a factor of 2. Indications are also given on the possibility of cylindrization of the focal surface.